Understanding Light and Color

Just as the visual system adapts from bright sunlight to a darkened movie theatre, the brain will become used to the light from a reddish-hued sunset, golden high-pressure sodium parking lot lighting or the cool blue of an afternoon sky. Just becausethe lighting looks normal, however dosent mean that colors in the space will be rendered well. Colors in which a light source is completely deficient will appear gray or black. Color critical spaces require a spectrally balanced white light source of CRI 90 or better.

Due to reflections, surface color can influence the color of lightin a space as can filters or finishes within a fixture, in general, warm color temperatures enhance decors done in warm tones, including many woods.

While 80% of our impressions of the world are visual, 100% of impressions are dependent on light and, therefore, lighting. This is especially true when considering color. The most detailed and powerful color scheme can be produced, but if the wrong light source is chosen, a dramatically different scene could result. It therefore pays to understand how light affects color in order to securely acheive the overall design goals.

Light and Color

Light is radiant energy that travels in waves composed of vibratingelectric and magnetic fields. Light waves have both a frequency and length the ranges of frequency and wavelenght differentiate light from other forms of radiant energy expressed on the electromagnetic spectrum, such as heat and radio waves.Certain light waves comprise a portion of the spectrum. This energy is capables of exciting the eyes retina producing a visual sensation.

Visible light however, is not really visible. it must strike an object fist, then be reflected into our eyes, Even a beam of light reaching into the night sky from a powerful flashlight is not visible to us-we are actually seeing light reflected from a multitude of tiny dust particles floating in the air

The visible light sqectrum is composed of different colors/wavelengths,from violet [380 nanometers] to red (about 620 to 760 nanometers). An even balance of these wavelengths composes pure white visible light. This can be physically demonstrated by shining a beam of white light through a glass prism; the light will be refracted into a rainbow of colors appearing from the other side.

We see objects because light strikes them, and the light is reflected back to our eyes This is also how we see colour. The surfaces of objects are chemically oriented to absorb all wavelengths of light except their "own color" which they reflect, and so we see the object as a shade of that color.

When electric lighting is employed,the color spectrum of the light Omay not be evenly balanced. for example, it may be saturated in blue and green wavelengths, and low in red, yellow and orange. As a result, if the object is blue or green, it will appear a rich blue or green; if it is red, it will appear darker and buller if the light source is low in red, black if red is non-existent.

For those who believe that perception is reality, therefore, the lighting designer has a lot of power over how the space is viewed by choosing the right light source. To choose the right light source, three standard tools are available: color temperature, color rendering and the spectral power distribution curve.

Color Temperature (CT)

Color temperature is anumerical measurement that describes the color appearnce of the light produced by the lamp catalog

For incandescent the color temperature is a true value; for gaseous discharge lamps, the value is approximate and results in a value called correlated color temperature(CCT). The difference is subtle enough that the two terms are often used interchageably.

The science behing determining color temperature values starts with atheoretical blackbody radiator,a block of black metal through which electric current is passed (performed as a computer model). As we heat the metal, it turns red-yellow, then white, then blue; as we measure the temperature of the metal at any givencolor produced, we then match the color to that temperature and produce a color temperature value.

In application, we use the color temperature of lamps to categorize them as warm, neutral or cool sources. the terms are not directly related to temperature; instead,they describe how the light source appears visually.warm sources actuaiiy have a lower color temperature (3500K or less), producing a red-yellow appearance. neutral sources (between 3500K and 4000K)have awhite appearearance, and cool sources (4000K and higher) have a bluish-white appearance. Daylight (summer sunlight), with a color tempereature of about 5500K,is a very cool light.

In design, the color temperature of the lamp will affect the visualappearance not of the lamp itself, lamps with a warm color temperature, for example,produce light that is saturated with red and orange wavelengths, producing of red and orange objects and lending a reddish tint to whites while darkening blues and greens.

In design, the color temperature of the lamp will affect the visual appearance not only of the lamp itself, but more importantly, objects in the room. Lamps with awarm color temperature,for example, produce light that is saturated with red and orange wavelengths, producing a richer appearance of red and orange objects and lending areddish tint to whites, while darkening blues and greens.

Warm light sources are traditionally used for applications where warm colors or earth tones dominate the scene, and where we want to impart a feeligh of comfort coziness and relaxation. Applications include the home, restaurants, lobbies and private offices. Neutral light sources are traditionally used for applications where we want to enhance all colors equally. such as supermarkets and stores cool light sources are traditionally used for applications where we want to enhance blues or stimulate the occupant to alertness and activity, such as offices and hospitals.

HID lamps may experience a phenomenon known as color appearance of the light source that can in a space. it is most noticeable in uplighting and wall-wash application Depending on the lamp type,it may be caused by operational age, operating phenomenon such as voltage dimming using a dimming ballast. To account for color shift due to operational aging, group relamping may be desirable. Ask the lamp manufacturer for more information about color shift and how its products perform.

Color Rendering :

Color rendition describes how a light source makes the color of an object appear to our eyes, and how well subtle variations in color shades are reveald. A lamp's color rendering ability is measured on the color Rendering Index (CRI),a scale from 0 to 100(although negative values are possible).Incandescent lamps have a CRI rating of 100. The higher the CRI rating, the better the lamp's color rendering ability is.The raing is provided in the lamp catalog. CRI ratings are only useful when comparigg lamps with the same color temperature.

CRI ratings are developed via computer analysis. First, a lamp with a given color temperature lights eight standard color samples, which is compared to a blackbody radiator at the same temperature. if the samples show no color shift between the two, the CRI rating is 100; if there are changes, a lower rating is given based on the degree of color shift. A high CRI rating means that the range of eight color will be rendered well, but it does not guarantee that any specific color will appear natural.

In application, iamps with a CRI rating of 80 or higher are considered to have "good" color rendering properties, causing objects to look "natural." Thanks to improvements in lamp phosphor technology, CRI ratings for fluorescent lamps have steadily increased, now offering a range from 48 up to 95 depending on the lamp.

In design, high-CRI lamps are ideal for color critical applications where color rendering and matching is important, such as clothing stores, groceries, graphic design studios and similar applications.

Color rendering is sometimes confused with color temperature. First, we must understand that color rendering is a comparative tool between lamps with the same color temperature as a base. if we choose alamp with a can effect richer blues and greens in the space; however, if we then choose a high CRI rating for that lamp, we can effect color enhancing for that lamp. In desigh, high-CRI lamps are ideal for color critical applications where color rendering and matching is important, such as clothing stores,graphic design studios and similar applications.

color rendering is sometimes confused with color temoerature. First, we must understand that color rendering is a comparative tool between lamps with the same color temperature as a base. if we choose a lamp with a cool color temperature. for example, we can rffrct richre blues and greens in the space; however, if we then choose a high CRI rating for that lamp,we can effect color enhancing for that weaker color, rescuing in a sense the reds, yellows and oranges from distortion and darkening.

Spectral Power Distribution :

Although color temperature and color rendering are useful tools in determining the color behavior of lamps, a more precise picture is provided by the lamp manufacturer in the form of a spectral power distribution curve (SPD).In a typical curve, we are essentially seeing the visible light portion of the electromagnetic spectrum. Incandescent lamps produce a smooth curve, low in blue and green and heavily saturated in red and orange.

Gaseous discharge lampsare characterized by spikes, which are generated by the arc, and low points provided by the flurescence of the phosphor coating. Lamps with improved phosphor coatings show a more continuous spectrum of energy, resulting in bettr color rendering. on the curve, therefore, we can see, to an extent, both color temperature and color rendering in action; We see what colors the lamp is saturated in, which are very low in energy or non-existent, and we see the effect of the phosphors at improving color performance. Because the SPD is somewhat complex, it is most useful when combined in analysis whit color temperature and color rendering.

They associated with a relaxed atmosphere and low light levels. Cool light sources are associated with brightly lighted, active environments. In addition to bules and greens, color sources flatter modern designs done in white, black, chrome and glass. A mixture of both warm and cool interior finishes calls for a neutral color temperature source, which also lends flwxibility for accent lighting and a middle-of-the- road ambiance.

Warmth and Luxury :

Warm colors lighted with dimmed incandescent sources create an inviting and comfortable atmosphere. accrding to an architect, specialising in hospitality industry interiors-warm sources the make people feel more comfortable. They instill more of a sense of well being and certainly luxury.

Because people have grown up with 2700K incandescent lighying in their homes, warm lighting is almost always the best choice for residential and hospitality applications,as well as high-end retail. The most important thing for me when choosing a light source is its color rendering capabilities, because designers spend an awful lot of time selecting the perfect colors.

Incandescent and halogen sources, at CRI 99+, offer the highest-rated color rendering among interior electrical sources. Newer fluorescent, compact fluorescent and metal halide sources in warm colors offer good color rendering in the 80s.

Though they are recommended for general lighting in many public areas, such as corridors where the lights burn 24 hours, experts complain that the lesser color rendering lends a "flatness" to finishes, furnishing, artwork, and flowers.

High Energy Environment

Cool colors are used to build excitement and reinforce the color scheme of this casino imterior. The cool colors enliven the space and reinforce the outdoor feeling of the space. At the other end of the spectrum, cool ambient lighting in the neighbourhood of about 5000K creates a very modern, high - energy atmosphere suitable for many public spaces, including lobbies, airports, sports venues and afst food restaurants. If theres a lot of daylight inthe space, you would probably tend to use the coolerlights, But there should be a method of warming up the light in the evening, as cool lighting at night becomes "refrigeratoe-like," very cold and unfriendly.

Dimming from higher light levels to lower will invariably bring out preferences for warmer colorts. In interiros, lower light levels and nighttime are associated with candlelight and a warm fire. Cool light is generally much more accepted for higher light levels and daytime. These preferences are propitious in that the cooler fluoroscent and discharge sources usually called upon to produce higher levels are much more energy efficient. Cool light sources are, however, perfectly acceptable outdoors at night, where the cool tone of moonlight is natural. Except for warm-toned structures, like brick or strucco, cool metal halide and fluoroscent sources generally provide standout facade and signage lighting.

Metal halide lamps are highly recommended for landscaping. The higher color temperatures do much better with the greenery. Mercury vapour can also make foliage stand out renders other colors not as wel. Metal halide are specially ssuited in parks and other outdoor areas designed for people.

Cool light with superior color rendering is often selected for art galleries - perhaps stemming from some artists preference for studios with northern exposures, which provide more consistent daylighting. But remember, no matter how high the color rendering index, a cool color temperature will bring out blues and greens in the artworks.

Neither does cool lighting fit comfortably with curators conservation requirements for lower light levels. Given that a lot of these works would have been painted under all sorts of lighting conditions, one has got a lot more flexibility and variety with tungsten halogen(color temperature - only 3000K).

Comfort and Flexibility

Neutral color lighting brings high-tech interiors and products to life. The light has good color rendering to accurately portray the colors of the interior and people using it while the whiteness of the light defines the environment as a definite space.

Neutral light sources in the range of 3500K to 4000K provide a wide middle ground, appropriate for most offices as well as a veriety of retail and other public areas. Good color rendering, triphosphor fluroscent lamps in 4000K compliment many of todays popular interior finishes : grays, blues, and greens. The cool and the warm colors come out pretty well, and skin tones look fine.