Bad habits never die

In these times of looking for the best lighting efficiency, “changing the bulb” for a low energy one is the predominant response to the issue. Additionally the idea that a “small” low energy bulb affects only marginally our general electricity consumption remain well rooted in the common mind.

The light reflected by the surfaces and that emitted by light sources interact to produce the spectrum that is perceived by our eye. Since colors and surfaces significantly affect the lighting of a space, good lighting can not be designed without considering the characteristics of the environment itself and especially the colors present in it.
Obviously individual taste in terms of decoration, such as wall colors and furniture, must be taken in consideration. But only as much as they do not end up multiplying “small” low energy bulbs, as, in the end, all these low energy light bulbs, plus some halogen in the hall, plus a pair of table lamps and a few spots, are capable of burning one third of our electricity bill at some times of the year.

Getting back to walls color, the first thing to understand is that the white is always the brightest color, or in other terms, that white is without exception always able to amplify the brightness of a space under natural or artificial lighting. Any other color subtracts a portion of the light that the walls are able to reflect and redeem to the surrounding. The idea, for example, that a yellow hue may increase the power of light’s reflection is utterly wrong. In reality, the luminance of a colored wall is always lower than the one of a white wall.

Furniture also impacts the brightness of a space. Not because of its color, but rather because of the quantity of furniture. How often do we see clutters of cabinets, ornaments, pictures, maps, tables, chairs and more darkening entire living spaces? Before you start filling every inch of white wall or every inch of floor you better consider how much this will cost you in terms of energy. And not only for lighting, but also for vacuum cleaning...

The proper rule is to use the light as a guide for the perceptual process, leveraging its ability to “underline” the space. The light becomes the channel between the object and its shape, adjusting the contours and dramatizing the space limits.

Minimal is not poor, it is essential

“Less is more” has greatly influenced modern design since German Architect Mies van der Rohe original citation. It has gained worldwide acceptance, strongly influencing U.S. architecture, but it is in Europe that it has picked, perhaps as a reaction to the continent’s rich baroque architectural heritage. Designers and architects have quickly adopted the new idea as it was allowing breaking free from a long tradition of rich decorative arts and looking instead for expression in its purest form.

As I stated earlier, minimalism’s most prominent attributes are geometric shapes, light, natural materials, space. A successful minimalist design is a result of a good balance between these elements, but it comes at a higher cost that you may think.

Minimal is not poor, it is essential.

Essential is the planning in the concept phase, a necessary and expensive step. Because it is about concealing clutter, a minimalist design cannot stand approximation, and every detail must be perfect.
Essential are the few materials used to set the stage in the large surfaces, perfect angles, flat finishes and solid colors that this type of design favors. They all tend to emphasize any defect, be it in a cabinet, a table or a door frame.

The quality of materials and workmanship must be outstanding, which also means expensive.

Focussing on people: perception

I explained before that, when we step into a room, our eyes are guided by light, and the light tells us the story of the room. A good lighting makes seeing easy and pleasant. It is a treat for the eyes.

Remember how in the early days of artificial lighting a room was usually equipped with one lighting fixture hanging in the middle of the ceiling. We all know today that this is barely the best way to light a room. The room appears smaller, as all light is concentrated in the middle, and the wall surfaces receive little or none of it. Furthermore, as light naturally attracts people, all activities also become concentrated at the center of the room. It is definitively better to spread the light over several areas of the room, each of them determined by its particular function.

But our perception remains highly subjective. When asking people's preferences about lighting, the opinions are often divided almost equally between a gentle, soft, friendly, almost shadow-free light and a harsh, fascinating, but also aggressive and glaring light with sharp shadows.

The first lighting is similar to a cloudy day. The second lighting reminds of a sunny day. The later seems slightly more popular, maybe because the first impression when entering the room is stronger and more interesting.

Focussing on people: working

Health and comfort are the most important prerequisites to our motivation, our productivity and to rich emotional experiences. Whether in the working world, in healthcare services, in hotels and restaurants or in boutiques, lighting has to be interpreted in a way that supports and promotes well-being and health.

Light has a great effect on our physical and mental state. In our quest to balance between movement and rest, between tension and relaxation, we need light that is modeled on the natural rhythm of daylight. We need to light with expectations.

The demands we make on our surroundings are continually increasing. This is particularly true of the quality of light, and of the design and aesthetics of the lighting fixture. Beyond the individual factors, it is important to consider the complete context: the characteristics of the rooms, workplaces and equipment, as well as the type of activities and the type of organization, so that the lighting design is tailor-made to suit the user and the specific environment.

Nowadays, an appropriate light management system has become indispensable and plays a particularly important role. The lighting control must be simple to operate, so that every user can regulate the light to suit the activity of the moment and in accordance with its own preferences. Pre programmed light scenarios and automatic daylight dependant illumination management also become standard in up-to-date illumination control.

In a working environment, an employer will express consideration for its employees and clients by providing high quality lighting solutions. Individual lighting control favors the appropriation by the employees and reinforces the feeling of belonging to an identity, and provides a positive corporate image for the outside. This in turn creates a positive impact on motivation.

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.

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.

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.

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.

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.

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.

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.

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.

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.

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.