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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