The color of a room’s lighting is a major factor in setting the emotional tone for that room. Light is what brings out the colors of the room and gives it the personality that you are trying to design into your space. Light is made up of different colors, and depending on those colors, an object or surface is enhanced or diminished. We see the colors of an object because the light falling on it contains the same colors as the object. The thing to remember when choosing the lighting for a room is what colors are going to be in the room, and will those same colors be present in my lighting design.
An object’s colors act as discriminate reflectors meaning they will only reflect their own color. The reason why we can see all the colors present in the objects around us is because white light contains all the colors of the visible spectrum of colors, so it highlights them all. This concept of how light works becomes important when we want to highlight something in a certain way. For instance let’s say we have a light bulbs red rose with a green leaf. If the rose was lighted with only a red light the green leaf would appear to have no color or it would appear to be black. This concept could also be flipped the other way in lighting the rose with a green light the red rose would appear to have no color or look black. Remember if the color isn’t in the light source you won’t see it in the object being lighted. When we look at the color light spectrum there are colors that are weak at certain points and stronger at others. If you have a light source that is stronger in any one color or colors it will tend to emphasize those colors and mask the other colors present.
When looking at and characterizing white light we use the terms “cool” and “warm” to describe its lighting characteristics and what part of the light spectrum it tends to emphasize. It does not describe the temperature of the light bulb. The terms “warm” and “cool” are emotional terms that tend to describe the experiences or actions that are performed in that light. For example a light source with reds and yellows are considered warm because they evoke feelings of relaxation and comfort, where a blue light source might convey a felling of cool water or the brisk outdoors. With this in mind you can see how a light source helps to bring out colors in a room and flood the place with certain emotions.
The proper name for color temperature is The Correlated Color Temperature (CCT). The CCT is described in degrees Kelvin (starting at absolute zero). It is backwards in a way, because when a color of a light source has a high temperature associated with it, it is considered to be a cool color, and if it has a low temperature it is a warm color. Lighting sources with a CCT rating below 3200 K are usually considered “warm”, while those with a CCT above 4000 K are usually considered “cool” in appearance. Using a light with a high Correlated Color Temperature will give a greater perception of brightness in the space than lower ones. When calculating a color temperature (CCT) we take the light we are looking at, and compare it to a Blackbody standard base line color model that has radiant power at all wavelengths of light, and where our color falls according to the base model will tell us what our color temperature is. Even at a given Correlated Color Temperature, color can vary. To avoid such variation, the EPA recommends you purchase bulbs from the same manufacturer at the same time. The color temperature rating is listed on the product packaging.
Now we can take the color of our light source that we are looking at and compare it with the Color Rendering Index (CRI). The CRI of a light source compares the color of the source to a Black Body color index of the same color temperature. The maximum Color Rendering Index number that is possible is 100. The higher the CRI of your light source the more natural colors will appear when illuminated by it. Light sources with a low CRI will distort the colors that are viewed with them.High (above 80) CRI is preferred in the home. ENERGY STAR requires that qualified fixtures have lamps with CRI above 80. Daylight and all incandescent and halogen light sources have a CRI of 100 and they are excellent at rendering color. For a warm lamp, the CRI is a measure of how close to incandescent color it is, and for a very cool lamp the CRI is how close to daylight it is. The lamps CRI should be listed in the Manufacture’s literature.
To review a Color Rendering index is a comparison of our light source with an index of the same color temperature. A Correlated Color Temperature (CCT) is described in degrees Kelvin, and it is a comparison of our light source against a standard base line color model that has radiant power at all wavelengths
Now we have talked about color temperature and the Color Rendering Index of a light source. In order to get a good picture of what the light source is going to do in our lighting design we need to consider both of them together. For example you can have two or more light sources with the same color temperature and they could be called warm but they render object colors differently. You can have Light sources with the same Color Rendering Index but different Correlated Color Temperatures and they could also render the object color differently. In order to get a more complete picture of how a light source is going to react to a surface you need to use both the Color Rendering Index of the light source and the Color Temperature of the light source together.