28 December 2008

Potential of LED control systems

Since the LED is a dimmable light source, the modular control of LEDs of different color allows a very precise shifting, fading and transitions of light, which in turn transmits a dynamic effect to the architecture set to ultimately communicate the idea of change and adaptability. The underlying purpose is to render architecture more efficient and sustainable, by creating a more comfortable, responsive and consistent relationship between the users and the architectural space.

Color mixing and color effects are seen as a powerful tool, positively provocative to our perception. Changing color can suggest moods and bring a healthy variability to the task of space-making. But this dimension of technology does not define a space by itself, as some extreme proponents of “interactive architecture” would have you believe. On the contrary, depending on how it is applied, it may even condemn spaces to becoming void of any kind of life. And this can happen fast.

Light always has a story to tell

the eye instinctively turns towards the light in order to see.

Lighting has a great significance to our well-being, health and safety. This is why it is such an important element in building and interior decoration.

Light is electromagnetic radiation invisible to the eye. Light only becomes visible when it meets a surface. Colors are formed by waves of different lengths, and when combined together produce white light. When white light is refracted through a prism, the whole color spectrum becomes visible, as in a rainbow. The human eye is only sensitive to the range of the “visible light” wavelengths, which is between 380 nm and 780 nm. The extreme ends of the scale being ultraviolet (UV) and infra-red (IR) light.

The human eye is perfectly able to adjust to the great variations of luminosity found in nature, from moon light (1 lux) to bright sunshine (100,000 lux). In artificial lighting conditions, we usually have to compensate for minor variations, from general lighting (1-2,000 lux) to working light (200-2,000 lux).

Our vision is based on light. The eye instinctively turns towards the light in order to see. Some 80% of all information is received through the eye.

When we step into a room, our eyes circle it guided by light, and the light tells us the story of the room: its shapes, colors, architecture, decoration, ornaments etc. A good lighting makes seeing easy and pleasant. It is a treat for the eyes.

14 December 2008

A simple life

Modern interior design and minimal living need not be cold and stern looking, nor should its serenity be purely monastic. It need not be so cutting edge either, that it becomes unusable or ugly. The essence is to find the level of simplicity that suits anyone of us. The only requirement is honesty to the materials and a respect of space.

Rooted in part in Japanese culture, minimalism, or one of its many incarnations, is a movement that started, originally in Scandinavia and Japan, as a reaction to the emergence of commercialized styles of architecture that was popping up everywhere with the idea of “less is more”. Minimalist design is concerned with minimizing the use of ornaments and “grandiose” designs in the structures. A few of minimalism’s attributes are geometric shapes, light, natural materials, space. A successful minimalist design is a result of a good balance of these elements. Minimal is not poor, it is essential. Essential in this case means that few materials set the stage for perhaps one or two important focus pieces. The quality of materials and workmanship must be outstanding.

Minimalist architecture is sometimes described as being cold, but advocates of this style find it more welcoming, relaxing and free from clutter. Depending on how it is planned, minimalist architecture can be elegant and at the same time, inviting. It makes use of the space as a feature and uses basic shapes and lines that are neat and can play with light resulting in an elegant outcome. There are many examples where the flow of space and light create the decoration without the confusion of ornamentation. Simple spaces gives rise to a more relaxed and tranquil life. In essence, living with less and finding more.

Blue light, yellow light

The quality and quantity of light influence the way we experience color: objects’ surfaces reflect only colors whose spectrum wavelengths are present in the illuminating light source.

The blue color is at its most beautiful in natural light because the incandescent lamp's yellowish light does not reproduce blue wavelengths. As today most indoor artificial light sources are still incandescent lamps, most indoor lighting is extremely yellowish. Consequently indoor blue colors under artificial light appear stuffy, even dirty and dull. They may even look greenish. On the other hand, yellows, oranges and reddish colors usually look good in the light given off by incandescent lamps.

In recent years, compact fluorescent lamps have proliferated as a result of their low energy consumption. Low energy consumption is an obvious economic advantage, but from the standpoint of color rendition compact fluorescent lamps are extremely problematic. They have an uneven spectral distribution, leading to situations where a colored surface may appear of a tint that has not been observed in normal daylight.

Because of the different kinds of spectral distributions in artificial light sources it is extremely important to check the colors in question under the lighting conditions where they will be actually used. Owing to its slightly bluish tint, natural light entering a space could significantly alter its color situation, unless the space has been designed with light source that imitate daylight.

01 November 2008

LEDs vs CFLs: bad answer to a bad question

Sorry to say but this article is typical of a bad answer to a bad question!

The first point is that the LED "bulb" is an abheration. Bulbs have been around in their present form factor because they break, burn or, in any other way, have to be replaced. Todays power LED have a rated lifetime 6 to 7 times that of the best CFLs, which when translated in understandable numbers amounts to a minimum of 8 to 10 years of normal usage in a household. So if something now is to break and be replaced in your instalation it will be the actual lighting fixture, that was never designed to last more than 3 to 5 years...

Second point, "Because of their structure and material, much of the light in standard LEDs becomes trapped, reducing the brightness of the light and making them unsuitable as the main lighting source in the home." is a biaised staement. This cannot be applied to lighting power LEDs, which are specifically engineered to reflect the major part of the emitted light. So when you speak of lighting applications, forget about these clusters of "many small LED bulbs together in a single casing to concentrate the light emitted" and choose a lighting source designed for real lighting applications.

Third point, what you are paying for is not due to "costly semiconductor technology". True, electronic components assembly can sometimes be more expensive than the "mechanical" components in an incandescent bulb. But the production cost for a 100 lumen power LED is today well bellow the 1USD mark. Even if we consider the multichips LEDs, which produce more than 1000 lumens, the production cost remain bellow the 5USD. Now, as I said, this is more expensive than incandescent bulbs, but you should really question your reseller as to where their selling price come from... Specially if they try to sell you the above mentioned "clusters" they get from the far east at a cost similar to those of the incandescent bulbs.

The proper answer to the title question is no! LED bulbs will not dethrone the CFL. New LED based lighting fixtures will replace our current fixtures altogether, but they will be tightly integrated and will probably have a vastly different form factor that the "bulb". LED is a disruptive technology which requires a different view point. But as we all know, ability to change is not the prime quality of Man.

14 October 2008

Beyond the love of our own crap

effective design is driven by insight, strategy and purpose.

In this time of induced uber-individualism, our day to day has been invaded by herds of people who “trust their own style”. What a perfect risk avoiding position, as anyone can both be author and critic of its own creation! How equally rewarding for the would be guru which can make a living of celebrating any new fad of fashion, art or design.

Submerged by layers of styles, pressured by their peers, subjected to the average crowd demand, how could a vast majority of “creative people” resist morphing into “stylists” and reiterating whatever the latest fashion happens to be. And the rest maybe tempted to evolve into “creative geniuses”...

We all fall in love with our own creation. This has probably something to do with the lovingly instilled early suggestions that all our expressions of creativity must be deemed significant. Nevertheless, these expressions can still suck.

Coming up with design solutions effective at reaching a broad audience is in no way less difficult or creative than making work that is personal in nature. In fact, as it requires keeping personal perspectives in the distance, in an effort to understand the situation from a wider standpoint, it soon becomes much more challenging,

Clients and designers alike fall into the trap of bringing personal aesthetics or style to projects. As that has usually nothing to do with the task at hand, the result is an enormous quantity of pretty but ineffective “design” out there.

Like for every other business, I believe effective design must be focused on results. Although it can use a multitude of instruments, it must not be personal in nature, nor follow degradable styles, unless this is really necessary. Effective design is driven by insight, strategy and purpose. It is about taking away the stylish and fashionable stuff in favor of what is actually accomplished.

13 July 2008

Heat is the great enemy of LEDs

Heat is the great enemy of Light emitting diodes (LEDs). This is ironic, since conventional bulbs produce light by heating a filament to such a high temperature that it glows. The most common way for LEDs to fail is by gradual decrease of light output and loss of efficiency. However, sudden failures can occur as well. All caused by excessive heat.

Driving power LEDs on constant current
LEDs use a different principle than incandescent or fluorescent sources to create light. LEDs are semi-conductors diodes that emit light when traversed by a current flow. LED diodes have polarity and, therefore, current only flows in one direction. A photo emission is taking place at the diode junction region when a DC low-voltage, constant current power is applied. Driving power LEDs is relatively simple as, unlike fluorescent or discharge lamps, they do not require an ignition voltage to start. Simply put, too little current and voltage will result in little or no light, and too much current and voltage can damage the light emitting junction of the LED. Consequently, to ensure a proper functioning of a LED light source we need some sort of power supply regulation.

When looking at a typical power LED forward voltage vs. forward current chart, we clearly see that, for a given junction temperature, a small variation of the forward voltage produces a large variation in the forward current. Conversely, as the junction temperature increases, the forward voltage across the LED drops as depicted on the forward voltage vs. junction temperature chart.

If we drive power LED light sources with a regulated constant voltage power supply, the forward current passing through the LED will increases as a result of a forward voltage drop, and in turn will generates additional heat in the junction. Ultimately, if nothing limits the current, the LED junction will fail by over heating.

Instead, by driving power LED light sources with a regulated constant current power supply, the light output and lifetime issues resulting from variation of the forward voltage can be eliminated.

Driving power LEDs for clean light
Luminous characteristics of power LEDs are specified for a specific forward current and a 25°C junction temperature. However most LED light sources are operated well above 25°C, and the “true” light output should be based on the anticipated operating junction temperatures.

As illustrated on the relative luminous flux vs. forward current chart, the light output of increases when the forward current increases. However the efficacy of the light source, expressed in lumens per watt, is adversely affected. Conversaly, the light output from LED light sources decrease with increasing junction temperature, as depicted on the relative luminous flux vs. junction temperature chart.

Therefore, when designing for specific light output, efficacy levels, wavelengths or color temperature, it is important to consider the effects of temperature and to maximize the thermal management of the application.

For a specific LED light source, the forward current may be chosen up to the maximum current recommended by the manufacturer. Driving LED light sources above that maximum may result in lower lumen maintenance or, with excessive currents, catastrophic failure.

High forward currents at elevated temperatures can cause diffusion of metal atoms from the electrodes into the junction’s active region, decreasing the radiative capacity through the creation of dislocations and point defects that produce heat instead of light. High-power LEDs are susceptible to current crowding, non homogenous distribution of the current density over the junction. This may lead to creation of hot spots in the junction, and increases the risk of thermal runaway.

When the epoxy resin used in packaging reaches its glass transition temperature, it starts to expand rapidly, causing mechanical stresses on the semiconductor and the bonded contact, weakening it or even tearing it off.

Higher junction temperatures resulting from increased power dissipation or changes in ambient temperature can have a significant effect on light output. Red and Amber AlInGaP phosphors are more sensitive to temperature effects than Blue and Green InGaN phosphors. Depending on the phosphor type, wavelengths can typically increase from 0.03 to 0.13nm/°C. White LEDs often use one or more phosphors. The phosphors tend to degrade with heat and age, losing efficiency and causing changes in the produced light color and slight shifts in color temperature. Similarly, some materials of the plastic package tend to yellow when subjected to heat, causing partial absorption, and therefore loss of efficiency, of the affected wavelengths.

Appreciating LED useful life time

With Light emitting diodes (LEDs), outright failure is very unlikely. Contrary to conventional lighting sources which typically fail suddenly or burnout, LEDs are solid state electronic components and as such gradually degrade. But because of their long expected lifetimes, conventional light sources’ life testing is impractical to estimate the useful life of LEDs.

Predicted Life Time
Useful life of conventional lighting sources is commonly expressed as the time to failure. This primary metric is based on the time it takes for 50% of lamps to fail. LEDs, being replaceable semiconductors, are using “mean time to failure” (MTTF) to express their failure rate. This is a well-defined statistical reliability metric commonly used in the electronics industry.
Power LED manufacturers typically predict high brightness LED MTTF to be on the order of 50.000 - 100,000 hours, provided LEDs “are properly packaged and used in accordance with manufacturers’ recommendations”.

Translating these durations in plain English, a LED light source would have an average life time between 5 and 12 years if left on all day. For “normal” general lighting usage, even when considering a 12 hours average daily usage, this would translate into an average life time comprised between 12 and 24 years. A very long life times indeed.

Average Lumen Maintenance
Even when operated within the manufacturers’ specifications, both conventional and LED light sources experience loss of light over time. This is known as lumen depreciation, and is typically expressed as lumen maintenance, i.e. the percentage of initial lumens remaining after a specified period of time.
If you have ever changed a light bulb, you have certainly noticed how bright the new bulb is compared to the older bulb, then you have seen the effects of lumen depreciation. Lumen depreciation in incandescent lamps mainly occurs by depletion of the filament over time and accumulation of evaporated tungsten particles on the bulb wall. In fluorescent lamps, it occurs by photochemical degradation of the phosphor coating and the glass tube, and by accumulation of light-absorbing deposits within the lamp over time.

LEDs also experience lumen depreciation, but many factors can influence light degradation, such as ambient temperature and humidity, drive current and thermal management. That said, the primary cause is heat generated at the LED junction. High junction temperatures accelerate degradation in lumen maintenance, but also result in a temporary reduction in luminous flux. Contrary to other light sources, LEDs do not emit heat as infrared radiation, so the heat must be removed from the component by conduction or convection. If a LED application has inadequate means of removing the heat, such as heat sinking, the temperature will rise and light output will decrease.

Let’s translate this into plain English. For general ambient lighting applications, the commonly admitted light output decline is set at 70% of initial lumens. If for example we are considering LEDs that deliver 70% lumen maintenance at a 50,000 hours rated life, it means we should expect to receive 70% of the initial lumens after 50,000 hours.

Lumen depreciation has to be taken into account when appreciating the “useful” life of very long life components such as LEDs. In short, the “useful” life time of a LED results from a combination of the MTTF and the lumen degradation. From an application perspective, a catastrophic failure of the semiconductor or the lumen performance falling below 70% always boils down to a degraded service. Because of the LEDs very high MTTF, LED applications are more likely to falter because of lumen degradation, which in turn is highly dependent on the appropriate thermal management.

28 June 2008

Lighting affects us more than anything in our home

Lighting is an art as much as a science. Lighting affects us more than any other detail in our home. Light conditions our emotional and physical comfort.

We need good lighting for our daily activities, to see clearly, to prevent fatigue, and to support our mood. We can light a room for a particular occasion or activity; we can change the usage of a space more quickly with light than with any other decoration detail. Lighting variations affect our daily rhythms giving us either a comfortable or a miserable mood.

Besides allowing us to see, lighting sets the emotional atmosphere. Understanding the effects of lighting is a key parameter when selecting light sources to create a particular emotional setting.

  • Bright light stimulates us, while low levels of illumination quiet our senses.
  • Too much bright light hurts our eyes and make us feel jittery.
  • Insufficient lighting causes eye fatigue and headaches.
  • Insufficient lighting is linked to emotional stress and to physical ailments.
  • Low light level or harsh contrasts produce eyestrain.
  • Directly visible light source cause irritation and disturb tranquility.
  • Artificial light does not replace the calming effects of natural daylight.
  • Absence of natural daylight triggers depression and poor immune defenses.

Lighting brings benefits in many ways, but notice how an excess or a lack of artificial light brings about the same harmful side-effects. Choosing between a glow and a bright light involves understanding the effects of light on our mood. Uniform lighting is adequate for working, but is rather boring; people feel more comfortable with lighting from many sources. Combinations of contrasting brightness and darkness cause dramatic and lively changes in an ambiance as long as they remain balanced. Use of artificial light sources add variety and vivacity to our spaces and our lives only by respecting our emotional and physical comfort.

02 June 2008

No retrofitting please!

Early attempts to apply LEDs to general lighting failed because LEDs did not meet the required luminous efficacy or color requirements. Technology has reached a point where using LEDs for general illumination is now a viable option. But, taking over where I left, I believe trying to repurpose existing technologies' lighting fixtures to house LEDs is inappropriate.

LEDs represent a disruptive innovation for the lighting industry. A disruptive innovation is technologically straightforward, using off-the-shelf components put together in a product architecture that is often simpler than previous approaches. These products are usually less capable in the traditional aspects of what is required in established markets, but feature different bundles of characteristics that were not considered important in the past. Applied to LED technology one may think of energy efficiency, resistance to vibration and unidirectional luminous flux, to cite a few.

Conventional approaches to developing power LEDs based general lighting often involve retrofitting existing fixtures to house the new technology. Many early attempts simply used traditional lighting standards and housings instead of investigating the challenges and benefits of LEDs. But LED technology breaks traditional rules, and it quickly become apparent that old thinking cannot be applied. A LED module may physically fit into an existing fixture’s housing, but that housing will not leverage the inherent qualities of power LEDs, mainly because:

  • standard housings do not handle the challenges of LED thermal management, which is vastly different from those of incandescent or fluorescent lighting.
  • optical design used in most traditional fixtures does not maximize the LEDs' efficacy.

Furthermore, power LEDs last a very long time, and the expectations for fixtures' life span are getting higher. Typical specifications for LED lighting fixtures tend toward more durable, longer-lasting products using higher quality materials than those commonly associated with other lighting sources. A state of the art LED module in a cheap fixture would defeats the purpose.

A disruptive innovation is not the same as a radical innovation. A radical innovation is just a major improvement along an existing performance dimension. A disruptive innovation creates a different performance dimension, one that is not particularly important to incumbent firms' most profitable customers. Let’s hope lighting industry experts accept the change and gain a better understanding of how to capitalize on that technology.

01 June 2008

The incandescent frame of mind

There is one recurrent bias in many writings about the coming of age of LEDs for general lighting: the author always assumes the only allowed form factors for LEDs to become successful have to be similar to those of the other light sources technologies we know today. Or to put it more simply, that LEDs are only going to succeed in the “retrofit” market. I take as example this attempt at describing how LED based fixtures are now able to compete with traditional general lighting fixtures.

Beyond the fact that the post speaks a little too much about one single manufacturer to be exhaustive, and try to draw general conclusions based on this narrow view point, I believe it gives a wrong perception of the issues at stake by providing the wrong examples. This is particularly true of the cost based examples. But I am ready to assume this has been caused by jet lag and "red eyes"…

Let’s examine the "much work remains to be done to get the costs down" example. First of all it sounds based on that ubiquitous chart found all over the web comparing luminous efficacy of light sources that everyone makes its own. Let’s say it makes me suspicious when I see a comparison using a "800 lumens" figure as a basis for calculation… But it is more the peremptory conclusion that "cost" must be driven down that makes me uneasy.

After all it is nor fair nor possible to compare the price of an incandescent bulb with a “15-20 watt LED”. Doing so we are not comparing apples to apples, but rather commodities with luxury goods, and ultimately we only propagate marketing BS.

As a matter of fact, the "cost" of this 15-20 watt LED light source is a retail price. Knowing that at semi-gross prices this same light source is coming out at around $27 (without volume discount), the only valid conclusion one can draw from the example is that the retailer is taking a three fold markup. And this cannot be called the cost of LEDs.

Moving on to the “kitchen cans” example, we can repeat the same calculation. This time taking into account the additional elements necessary to create a retrofit light source, namely a constant current driver ($5), an anodized extruded heat sink ($2), an optic ($3), an outer fascia ($1) and fixtures ($1). We are now approaching the $40 for the bill of material. The resulting product will probably be assembled in China, adding another $5 to the cost. Once again the example only demonstrate the three fold margin applied by the retailer on the product.

However, I agree with the author that “only the most elite pocketbooks will open for LEDs” at this price. Like they did for incandescent bulbs when electricity lighting took over from gas lighting… But what a cumbersome way to say that most retailers are pricing LED retrofit light sources as luxury items! Hasn’t it always be the case with emerging technologies?

Nonetheless, to return where I started, I believe the author missed an important point. Power LEDs are a disruptive innovation and trying to mold them into the previous technologies form factors is flawed. LED general lighting will really take off when designers, writers and customers alike will step out of their “incandescent” frame of mind.

31 May 2008

LED or Luminous Efficacy Demystified

Efficacy, power and costs of high power LEDs have now reached levels that make them attractive in general lighting applications.

The luminous efficacy of a light source is the ratio between the emitted luminous flux and the amount of the absorbed energy to transmit it. It is expressed in lumen/watt (lm/W), where the lumen is the measure unit of the luminous flux. However, the lumen is based on the subjective perception of light by the average human vision, corresponding to a particular curve inside the visible spectrum. To put it simply, a standard incandescent light emits radiation both inside and outside the visible spectrum. The radiations emitted in the infrared and in the ultraviolet do not contribute to our perception of brightness. A light source will have a higher luminous efficacy as much as it will be able to emit in a spectrum suitable for the human vision.

The LED technology has made significant progress on the emitted power front. Today standard high power LED are available in 1, 3 and 5 watt, and multi-chip emitters are becoming available that push LED power towards the 15 watt. But above all high power LED have ten times more efficacy than the incandescent sources. Every serious manufacturer offers high brightness LEDs with minimum luminous efficacies well above 80 lm/W. Nowadays 100 lm/W minimum luminous efficacies are quickly becoming the norm for white light.

To quickly illustrate the point, a 60 watt standard light bulb, with a source efficacy of 15 lm/W, produces a luminous flux of 60 x 15 = 900 lumens. A light source built with nine 1 watt high power LEDs, with a luminous efficacy of 100 lm/W will produce the same luminous flux, but will use only a power of 9 watt instead of the 60 watt of the standard light bulb.

For a more accurate comparison between different lighting systems we must take into account the entire system that produces the luminous flux:

  • Source luminous efficacy (lm/W): it is the primary luminous characteristic of the light source, and varies according to the given technology.
  • Electrical efficiency (%): it defines the incurred losses to adapt the standard electrical source to the need of the considered technology. For example, incandescent lamps are directly connected to the power line without any adjustment. This is not the case for other technologies such as the fluorescent lamps, which require ballasts with 60-70% efficiency. Similarly, an inverter for compact fluorescent lamps has an efficiency of 80-90%, while an AC/DC driver suitable for LEDs can have an efficiency higher than 90%.
  • Fixture efficiency (%): standard incandescent and fluorescent light sources radiate in almost all directions and require reflectors and diffusers to shape the light beam for the required application. These systems have an efficiency which is usually estimated between 30 and 50%. By comparison, light emissions from LEDs are inherently directional, and 95% efficiency can be assumed.

Taking into account the entire chain, the efficacy of incandescent lamps will be as low as 7 lm/W, whereas fluorescent will achieve 38 lm/W and high power LEDs reach 76 lm/W. A better evaluation of the electrical power necessary to produce the 900 lumens would give 128 watts in the case of incandescent lamps, 23.8 watt for fluorescent fixtures and 11.8 watts for LEDs. A significant energy saving!

18 May 2008

Evolving view points for an evolving technology

To me a great majority of blog posts talking about LEDs are frankly disappointing. Although some try to take an exhaustive approach at presenting the technology in terms that can be understood by anyone, their content often remains static and academic, often copied from the same source. As these blogs are likely to come on top of the search engines responses, the casual reader may end up drawing the wrong conclusions with regards to the usability of the LEDs technology. Obviously at this point in time it would be biased to present LEDs as “the” perfect, “do-it-all” technology for general lighting. But this is a fast evolving technology, and, as for computer hardware, Moore’s law is applicable: today’s “truth” may become obsolete within a year or two. As a result, one has to remain cautious when presenting LEDs technology strengths and weaknesses.

In general lighting applications LEDs have advantages and disadvantages when compared with other light sources such as incandescent or fluorescent lamps. When looking at the positive side, the most significant advantages are fast turn-on, lower heat generation, lower power consumption, higher operating life, and high resistance to shock or vibration.

On the negative side, many blog have not been updated and retain obsolete information which may induce the casual reader into drawing hasty conclusions. Amongst the recurring limitations these blogs describe are the narrow viewing angle, and the need for electronic driver circuits to operate.

Starting by the later, LEDs need to be driven properly to ensure optimal performance and long life. An effective driver is key in obtaining all the benefits of LEDs. If early driver's implementations made of discrete components were not cost effective, this is not the case anymore. Pushed by the fast adoption of LEDs in the automotive and aeronautical industries, today almost every integrated circuit manufacturer proposes a vast array of LED drivers to suit almost every aspect of general lighting requirements. Furthermore, the leading manufacturers’ constant current sources, which until recently were only able to drive a limited number (usually 3 to 6) of power LEDs have recently been superseded by new affordable sources with 3 to 4 times more capacity.

Let’s now look at the viewing angle. First of all, light emissions from LEDs are inherently directional, thus reducing the need for reflectors and diffusers that can trap light. As a result, general lighting LEDs fixtures can potentially deliver light more efficiently to an intended location, leading to potentially higher application efficiency than other light sources in certain lighting applications. By comparison, fluorescent and incandescent lamps emit light in all directions. In their case, much of the light produced by the lamp is lost within the lighting fixture, reabsorbed by the lamp, or escapes from the fixture in a direction that is not useful for the application. For many fixture types, it is not uncommon for 40-50% of the total light to be lost before it exits the fixture.
Now, if the early generations of power LEDs were exhibiting narrow light emission angles (from 30º to 50º), the latest generations emit light at much larger angles, between 120º and 160º. This cannot be qualified as “narrow” anymore, and opens up new general lighting applications to the use of power LEDs.

Once again, as in too many cases of emerging technologies, the information for the public tends to remain far behind the actual technical advance...

16 May 2008

Display of power

Yesterday as I was reviewing various power LEDs’ technical datasheets, trying to extract useful parameters and feed them to my lighting design software, it struck me how manufacturers use such diverse ways to express the same characteristics of their products.

Luminous efficacy, expressed in lumen/W, is one of the most important parameters for lighting design. But when it comes to high power LEDs, it can be wrongly interpreted. It is probably the result of using a simplified description for these LEDs calling them 1W LEDs.

In effect, the actual usable power in the LED is equal to the driving current multiplied by the forward voltage. The latter changes significantly between LED families of the same or different manufacturers, and may vary according to application usage between 3V and 3.6V.

For LEDs driven at 350mA, the usable power will vary from 1.05W to 1.26W, inducing a 20% variation of the emitted light flux, which is certainly not to be ignored. By the way, this is the power value to be used when comparing luminous efficacies, as it includes the small amount of power wasted as heat in the LED.

15 May 2008

Did you say white LED?

The LEDs (Light Emitting Diode) are semi-conductor diodes that emit light when traversed by a current flow. A photo emission is taking place at the diode PN junction region, and the total quantity of emitted photons, therefore the light intensity, is proportional to the current intensity that passes through it.

The spectrum of the emitted light is primarily defined by the type of materials used to build the diode's PN junction, although it also depends on the current’s intensity and on the junction temperature.

LED manufacturing uses diverse technological process variations that lead to the production of different families of light color, such as:

  • Gallium arsenide (GaAs) for light from infrared to red (650 nm);
  • Gallium arsenide and phosphate (GaAsP) for light from red to yellow (630-590 nm);
  • Gallium phosphate (GaP) for wavelength from blue to green (565 nm);
  • Gallium nitride (GaN) for blue light (430nm);
  • Indium and Gallium nitride (InGaN) for light from deep blue to ultraviolet (390 – 360nm);

The white power LEDs are usually based on blue LED chips of the more recently introduced InGaN family. The white color is produced using a blue light chip covered by one or more semi-transparent layers of phosphors. Using the light’s complementary color combination, appropriately chosen phosphors layers combined with the base blue light allow the creation of various white lights.

As a result, today’s white power LEDs generally behave like the InGaN products' family, with some variations, due to the presence of the phosphors.

14 May 2008

Is the general lighting industry ready for LEDs?

Reading this post I was wondering if today’s lighting industry is ready to design and produce power LED lighting addressing general users’ needs.

LED technology is something we have been hearing more and more about from television, magazines and news reports. However, very few people understand why this light source is such a powerful alternative. The advantages of LED light sources over traditional lighting sources are numerous but can be simplified into energy efficiency, longevity, power and versatility. Despite these advantages, creating power LEDs based lighting fixtures is challenging because the technology and the associated constraints require a different knowledge from the traditional general lighting know how. To highlight just a few differences, a power LED based lighting fixture generally involves:

  • a number of electronic components which are not usually found in today’s standard lighting fixtures,
  • a thermal management system to ensure the proper functioning temperature of the semi conductor which produces the light,
  • an optical system to propagate and adapt the light for the specific purpose of the lighting fixture.

Beyond these technical differences, I see two major human reasons behind the slow adoption of LED technology in general lighting:

  • the rather feeble interest shown by designers of general lighting fixture for the technology
  • the heavy investments made by the industry in trying to make existing technologies more efficient

First of all, the components of power LED fixtures come in different form factors and present different usages patterns from what many lighting professionals, including designers, are using in their day to day work. In summary, using power LEDs requires a different type of knowledge, which in turn implies a certain learning curve.

Besides, I am under the impression that many interior lighting designers behave as stylists, “kooky kids” who like to do fun, pointless things, being more preoccupied by the actual “look” than by the “function” of the lighting fixture. When a given style becomes “hot”, legions of designers imitate it until it is everywhere, and as a result, most of today’s interior lighting designs boil down to flurries of boring light shades and diffusers stuck around inadequate incandescent, halogen or fluorescent sources.

As to the manufacturers, their weak interest make me believe that they re-iterate a well known incumbent behavior: they dismiss a disruptive technology to “protect” investments made in the previous technology. Furthermore, LED manufacturers only address part of the overall market, forgetting to properly educate other sectors of interest. This is particularly obvious of power LED manufacturing, where a vast majority of today’s production is destined to the automotive industry. Obviously, with the ever increasing amount of electronic in our cars, automotive engineers do not seem afraid of an additional “pile of semiconductor chips” and certainly know how to put them to good use.
Unfortunately, the same does not apply the general lighting industry! There, in view of the substantial investments made over time in studying, designing and using the current range of halogen and fluorescent lighting, everything looks like the adoption of power LED technology will take another century.

Finally, there is a split within the general lighting industry regarding the form LED luminaires should take. Some manufacturers are focusing on producing LED light sources that will accommodate existing lighting infrastructure and resemble existing decorative and task lighting fixtures. In my view doing so is rather short sighted, and wastes the potential of a promising technology. A better approach is, in my opinion, to design new light source formats that will deliver lighting in unexpected and innovative ways that could not be accomplished with previous lighting technologies. The fact that LEDs can be incorporated into just about any material, including fabrics, means that lighting could be made to emanate from the very surfaces and shapes of objects, from architectural elements to furniture.

At the risk of sounding overbearing, I believe some of these attitudes by the industry's actors delays a particularly attractive and efficient technology and limit the opportunity of participating to higher level discussions. In particular, although it is unlikely that incandescent lamps will be banned outright, the lighting efficacy standards under consideration all over the world would set minimums so high that most incandescent lamps would become ineligible for use by 2012 at the earliest. In this context, the lack of traditional sources efficient enough to meet the proposed efficacy standards will leave a huge gap in the market, that could be partially filled by LED lighting fixtures and luminaires.

25 February 2008

Out in the midday sunshine

With a color temperature of 6000 ºKelvin, noon sunlight renders neutral colors. It has a color temperature similar to that of flash systems.

It is light that enhance or blur a detail. It is light that creates the illusion of depth, underline the textures and establish the ambiance.

When the sun is at its highest point in the sky the light is at its whitest and strongest. Contrast is very high. Shadows are very dark, so dark in fact that they generally appear black, although it is still possible to see some detail in the shadows.

To complicate matters, atmospheric haze and reflections become much more visible. Haze and reflections cause bright colors to lose saturation and wash out. They appear to be less saturated than at other times of the day. The strong contrast makes it difficult to appreciate objects, and above all "white" skin, in this sort of light. Shadows will "block up", highlights will blow out, or both. However in situations where contrast is naturally lower it can produce very appealing scenes. Water for example can really benefit from this strong light.

At noon, the small shadows and strong light are not very good at revealing or enhancing forms and details, and the low color saturation adds further flattening to a scene.

24 February 2008

In the gloaming

In the gloaming, the air stills, birds sound their final calls of the day, and the light often turns golden; we find ourselves introspective as our visual perceptions, attitudes and pace of life shifts. The gloaming symbolizes intertwining of the dark and light.

"Gloaming" is the Scottish word for twilight, that transition time between the day and the night. It is recognized by the presence of weak sunlight, while the sun itself is below the horizon.

On clear days, there is always a yellow, orange or sometimes pink glow to the west where the sun is illuminating the sky from below the horizon. Whereas the glow from the sun can last for over an hour after sunset, the color in the eastern sky is much shorter lived, and changes very fast. In overcast conditions the skylight is always blue and generally much darker, with night falling more quickly.

On clear days, there is often a pink area in the eastern sky at dusk. This phenomenon is called alpenglow. Alpenglow cast a noticeable pink light onto reflective surfaces, such as white walls or water, but is too faint to affect darker surfaces such as foliage. As a result the landscape can look very dark at this time. When the weather is overcast, the eastern sky is just blue.

Twilight is a very special time of day with unpredictable but often very beautiful lighting. Since the sun is not above the horizon, the sky itself is the only source of natural daylight. As a result the light is very soft, with little shadow and contrast and the colors can be very delicate but vividly saturated.

23 February 2008

The ultimate sidelight

The light changes rapidly at sunrise and sunset. With the sun low on the horizon, the color temperature of the light could get as low as 2000 ºKelvin, giving these moments their characteristic yellow, orange, pink and red tones

As I mentioned earlier, the largest changes of natural daylight are at sunrise and sunset. Furthermore, if one observes several sunsets and sunrises in succession, it becomes obvious that they are very varied in terms of color and atmosphere: in fact no two one will be the same.

Sunset and sunrise light is the best sidelight, because at those times the light is horizontal. As its name implies, horizontal light is parallel to the horizon, and when grazing an object will give it a strong three dimensional quality. We perceive this sidelight as aesthetically pleasing because it enhance our three dimensional perception.

At sunrise and sunset, the sun is just above the horizon, and sunlight has to go through many layers of dust, haze and pollution before it reaches the earth surface. During this travel, as dust and haze scatter the sunlight, its intensity is greatly diminished and softened. The scattering also removes the green and blue radiations, leaving mostly the red part of the visible spectrum. As a result, sunrise and sunset light is warm, and depending on the particular day, tinted of pink, red or orange.

Sunrise and sunset light is also rather weak, which in turns means that contrast is very low. This weak sunlight also means that skylight takes on a greater importance and shadow areas become a deeper and richer shade of blue. Shadows at sunrise and sunset are very long, and any texture is very apparent.

The combination of diffused light and of the warm glow of sunrise and sunset creates a light which is extremely pleasing to the eye. If there are any clouds, the sky during these moments can be incredibly colorful. Unlike during the rest of the day, clouds are lit from below, and usually take on dramatic red or orange hues. The reflection of these colors adds complexity to the color of the skylight, and shadow areas sometimes turns purple or pink.

22 February 2008

The effervescence of natural daylight

Artificial lighting of the future will give off natural daylight.

And to that extent will probably remain an illusion, as natural daylight can only ever be grossly imitated.

Natural daylight comes in a wide variety of forms, and the difference between each of them can be enormous. The source of all our natural light is the sun; however it presents very different characteristics at different times of day and in different weather conditions. Instead of a single source of light we end up with many different ones ranging from hard to soft and warm to cool. Without preaching the obvious, two very common observations are enough to be convinced of the extraordinary dynamics of natural daylight.

Sunlight has a different character at different times of day. Our atmosphere scatters the shorter wavelengths of light with the effects of creating the blue of the sky and reddening the light from the sun itself. The thicker the layer of atmosphere that sunlight has to travel through, the more scattering occurs. This is exactly what happens as the sun gets low on the horizon, thus causing more scattering at the beginning and the end of the day.

Clouds also have a major influence on both the color and the character of sunlight. Clouds are translucent. They let light pass through in a diffuse manner, deflected by the water mist they contain. Rays of light are bouncing around to emerge from several directions. This phenomenon is similar to the scattering of blue light by the atmosphere, except that in clouds the scattering occurs across all wavelengths, not just the shorter ones. Clouds also affect colors, since they usually hide the blue sky and the light emanating from it.

21 February 2008

Are we all designers?

We live in times where the surge for expressing one’s individuality and personality is stronger than ever before.  Every moment, we consciously or unconsciously try to recreate our own identity to escape the void of anonymity. This expression can take many faces, from the style of clothes we choose to wear, to the way we modify the environment we live in, including our own homes. But in the end, it always revolves around asking ourselves what suits us, how we see ourselves and what combination of different objects can provide points of reference for us.

The age of the homogenous style is long gone. Living requires a collage of different styles and special features. Any personal style evolves from an epicenter around which gravitate the most varied influences and inspirations. There’s not just one trend anymore when individuality imposes over six billions of possible style mix…

Design takes its inspiration from a context, but that context has become everyday more widespread. We live in a sort of "constantly self re-designing" society, which calls for the intersection and combination of disciplines, as well as ever more precise concepts of the emotional traits of objects. The answers offered by designers must therefore be as multiform as our requirements are individual.
Lights form an integral part of the architecture of the places where we live. This is true of public and private buildings, as well as of spaces used for business or entertainment, internally and externally. Not only does lighting create spaces that are safe and properly illuminated, but it also provides mood and ambiance.
For lighting design it will mean spreading itself and look for new strategies, aesthetic concepts and design approaches, capable of providing that required flexibility and adapting to our always changing moods.

It is clear that lighting design is developing in very different directions, none of them close to becoming a trend, but rather aimed at satisfying our personal preferences and individual ambiance’s ideas. Furthermore, we are already seeing how conventional lighting categories and classifications are increasingly questioned in the face of the solid state lighting revolution. These new light sources, in their current LED form or in that of OLED later, open up a large variety of approaches to lighting, and will induce new objectives, ideas and processes to cope with our quest for an appropriately styled individuality.

More than ever before, artificial lighting requires a novel interpretation because, as light itself, it makes profound statements about the stance, origin and value on our own individual aesthetic and emotional system.

27 January 2008

Deceptive and elusive color...

From the glow of dawn to the brilliance of midday, from the cast of twilight to the exuberance of sunset, the constantly changing color of natural light is part of our existence. As I explained in my previous post, there is no formal definition of "true" color. When we view objects under different types of light sources, we notice differences both in the light itself and in the way surfaces are rendered under these different light sources. Whether the light comes from a natural or an artificial source, each spectral distribution distorts colors. Color quality remains very subjective, and the existing measures of color quality created to allow comparing and evaluating light sources are far from perfect.

As I hinted above, the color quality of light has two parts. The most obvious part is whether the light appears “warm” or “cool” and is expressed by the Color Temperature of the source. The other part is the ability to reveal the relationship between colors and is referred to as the Color Rendering of the source.

The Color Temperature of a light source describes the color of white light, its yellowness or blueness, its warmth or coolness. The term temperature refers to the real temperature of a physics concept called ‘black body’. The everyday equivalent of this concept can be seen in materials such as iron, which gradually glows when heated. Their color change as a function of temperature: first red, then orange, then yellow up through white and blue. The temperature of the material which corresponds to those colors is termed the color temperature, and is measured in degrees Kelvin (K) on an absolute temperature scale.

The Color Temperature does not define how natural or unnatural the colors of objects will appear when lighted by the source. Two light sources can have the same Color Temperature, but render colors very differently. For example, fluorescent lamp may have about the same Color Temperature as do high power incandescent lamps, but they have far less red energy in their spectrum. Therefore, red colors will not appear as bright as they would under incandescent lighting.

To help indicate how colors will appear under different lighting conditions, a measure has been adopted to assist in comparing between different light sources. Called the Color Rendering Index (CRI), it is a relative comparison between a light source and a reference source.

A simple definition of CRI would be how an artificial light source shifts the location of eight specified colors as compared to the same colors lighted by a reference source of the same Color Temperature. If there is no change in appearance, the light source is by definition given a CRI of 100. From 2000K to 5000K, the reference source is the ‘black body’ and above 5000K, it is an agreed upon form of daylight.

There are several limitations to CRI. First of all, it is a simple scalar value and it is difficult to believe that a single measure can reveal everything about the quality of a light source. Light is a rich space of hue, saturation and brightness, in which light sources with vastly different spectral distributions can have identical CRI values yet render colors in very different ways.

Because it contains substantial distortion, especially in the red region, the color space used for CRI calculations has become obsolete. With only eight colors, the set of reference colors provides a rather reductive sample of colors given the breadth of the visible spectrum. Furthermore, it lacks the richer saturated colors, even if observation reveals that the most dramatic color shifts occur in the saturated colors!

A common misunderstanding is that high CRI means that the light source will render all colors well. This is not the case. CRI is measured only with respect to a reference source. For the comparison to makes sense, the reference must be the closest in color to the source being tested.

Another mistaken impression is that a higher CRI value comes closest to approximating natural daylight, but this is incorrect. There is no single measure of natural daylight as the color of the sky and the light from it can vary significantly over the course of a day and according to the viewer position.

Incandescent lamps have a CRI rating of 100, yet are far from ideal for color rendering. Their CRI value simply means that the 8 color samples look exactly the same as they would under a "black body" radiator at 2700K. But at this Color Temperature incandescent lamps are far too weak at the blue end of the spectrum, making it almost impossible to distinguish between various shades of blue. The same can be said for light sources with Color Temperature above 6000K as they are too weak in the red end of the spectrum, making reds and oranges appear similar. The northern sky with its 7500K and a CRI of 100 is not a good color rendering light source either. An “ideal” light source for color rendering will have both a Color Temperature similar to daylight, i.e. in the 5000-6000K range, and a high CRI value.

In a way, the CRI measurement method attempts to quantify a subjective notion, and as many such attempts is far from giving reliable results. To further support the subjective nature of CRI, in one study LED light sources were compared to reference light sources. It turned out the LED light sources were preferred over halogen and incandescent light sources for overall color appearance and that CRI had no correlation to people’s color preference.

To avoid specious marketing strategies, the educated consumer need only remember that Color Temperature isn't by itself a metric of performance. It is typically a specification of the type of light source, and is used to describe the color of white light.

On the other hand, the Color Rendering Index is the metric used to compare the color quality of light sources until a new and accepted measure is developed. However, CRI is controversial and presents several deficiencies, especially with respect to LED sources.

16 January 2008

Incense, candles, and Patanjali

Nowadays a signature scent means more than the perfume you choose to dab on your pulse points. Our personal spaces are just as important for conveying fragrance fancies. While there are people who take great care of finding the perfect perfumed candle to match their décor, there are also those who rely on a Glade plug-in to set the scent. Our venture into the home fragrance diffusion is definitely for those in the former category.

From our multifaceted approach to the lighting of space, we have experienced lighting as the single greatest determinant of how a space feels. But we also know that, while light triggers emotions and feeling in our brain, olfactory experience sets mood. Combining these two sensations was the cornerstone behind the genesis of the Patanjali® Perfume Diffuser.

Incense, candles, perfume-burners, lamps or sprays: down through the ages, the art of perfuming the home has become increasingly sophisticated. It nevertheless remains essentially based on three principles: heat, combustion and spray.
To that effect, our system efficiently combines lighting and fragrance diffusion. It re-cycles the low heat energy of its light source and uses it to diffuse essences placed in small perfume containers. Thanks to the low power consumption of its advanced solid state source, the temperature in the containers remains close to that of the human body temperature, and participate in very natural fragrance diffusion.

Light gives life, whether it is life in the larger sense or life in the individual home. So it is natural to place rigorous demands on the lamps that illuminate our surroundings. The Patanjali® Perfume Diffuser is a fusion of rigorous design and careful craftsmanship. This perfume diffuser is very unique in design, very modern yet not too flashy. Whether on or off, it ensures a functional lighting, and at the same time offers an aesthetic experience. The subtle shade prevents the light from glaring, yet it can light up the ambiance of a room.

The Patanjali® Perfume Diffuser transcends its original illuminating function. Its light surprises, suggests contemplation, triggers imagination. Add a sultry scent and you create a complete emotion.

15 January 2008

Pigmenting imagination

Color is not a physical property of objects, but rather our physiological and psychological response to light reflected by these objects. Carl Ingling once said:

"color is only a pigment of your imagination".

The first impression of the color of a room should not be taken too seriously - it will change with time. Just as the body adapts to the temperature of warm water so will the eye adapt to color.

We commonly describe white light based on associations with other colors. Yellowish white light, perhaps reminding people of a wood fire, is called "warm", while bluish white light is called "cool."

All light sources used in general lighting will gradually shift in appearance to become "white" to the viewer, whether they are “warm” like incandescent lamps and high pressure sodium lamps, or “cool” like daylight. Our color vision tends to compensate and fill in for those colors that are lacking in the light source’s spectrum: red in the case of daylight, blue for incandescent, etc.

As in the case of many other human perceptions, we are only sensitive to variations of color and not to the color value itself. Therefore, the eye's previous state of adaptation is significant. A “warm” space will look even warmer to the occupants if they enter it from a “cold” bluish space. It will look cooler if they come from a yellowish or pinkish one. But then the eye will slowly adapt until the space appears to be lighted with "white" light, no matter what the eye previous adaptation was.

While side-by-side color comparisons are an excellent way to show the differences between two light sources, since the eye never becomes completely adapted to either source but to a combination of both, a proper color evaluation is best achieved:

  • using a relatively large space,
  • lighting one light color at a time.

The ultimate test is to live with the colors for an extended period of time, in that way adaptation effects are accounted for.

The light from an electric light source is not inherently different from the light of the sun and the sky. In effect, visible light sources vary only in the relative amounts of energy at each wavelength. That however, is important because it is visible and we react to visible stimuli.

There is no "best" color lamp, nor is there any formal definition of "true" color. Each light source distorts objects’ colors, whether the light comes from a natural source such as sunshine or sunset, or electric sources such as incandescent, fluorescent or LED.

But there are certainly strong preference factors associated with light and color just as, for example, when people select clothing, furniture or decorations for themselves and their surroundings. The "right" light source for a given application largely depends on these personal preferences, custom and, in growing proportion, on an evaluation of the trade offs in efficiency, cost, and color rendition.

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Form is the visual shape of mass and volume. Light makes form legible. There is no form without light.


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