When evaluating which colors to mix in response to a light source, it helps to first identify the source as being natural or artificial. This is because the two emanate distinctively different temperatures. As a general way of looking at it and for simplicity's sake, we can say that natural light is cool and artificial light is warm. Natural light (light coming from the sun) is generally whiter (cooler), or known as balanced light. Artificial light (man-made light or light bulbs) is generally warmer. Let's investigate both these scenarios.
How an artist sees light
Let's begin with natural light and how it impacts our color mixing.
Natural Light (light coming from the sun) is cool. This doesn't mean you're not going to use warm colors in your lights such as yellows, reds, oranges and warm browns. Yes, you will use these warm colors. However, you will use them with some amount of white added into the mix. This is called a tint or tinting a color. A tint is the mixture of a color with white. It is critical that a painter is aware of when white is added to a color you are automatically cooling-off and making less intense that color, it becomes a tint of that color. The color is in a way deadened or neutralized by adding white to it. It helps to think of white and black having the same neutralizing affect on color, they subdue color.
Artists refer to the temperature of natural light as being cool (this is, of course, an exception to sunrise and sunset). The brighter the sunlight, maybe too, the more white added and washed-out the color becomes. For instance, red is intrinsically warm. However, once white is added to it it then becomes a lighter tint of red and, as a consequence, it becomes cooler. Pink is just another name for a cool red. Instead of calling it "pink" an artist more accurately identifies it as being red with however much white added to it. The word "pink" is less descriptive and is really not as much use a term for an artist's vocabulary.
What is important is that the red's intensity has been lessened by the white. An artist now begins to more accurately make a distinction between the amount of red vs. the amount of white in the mix. This is valuable to a painter because a painter needs to be able to gauge the intensity of a color and how much white may be in it, its tint.
The science of light
Forget you are an artist painter for a moment. From a scientific perspective, natural light is generally refereed to as cool because the sun burns both extremely bright and hot, commonly known to artists as white light or perfectly balanced light (not too warm and not too cool).
Earth's atmosphere is why natural light is sometimes seen as a cool blue. Our dense atmosphere is made up of water particles that absorb most all the color bands of light, letting go of blue. This refracting and reflecting light is also what makes the ocean look blue. A brief exception occurs during sunrise and sunset. While the amount of light (Lumen) is slowly diminished during sunset, so too does the bright white light and it begins to warm to that of a candle before it's extinguished. The light that does remain has to pass through our dense atmosphere at a more extreme angle to the horizon—where the pollution also cares to dwell. Light passes through pollution particles and further contributes to a warm light cast. The opposite scenario is true... the hotter and brighter a light source gets the cooler the light is perceived.
Artificial light
Artificial light (light emitted by manmade light bulbs) is probably the most complicated of all the light sources because of the many different types of bulbs on the market. Although in the past artificial light was known as being warm. However, these days, the many different types of bulbs offered can be warm or cool or even in some cases, perfectly balanced. An artist must have an understanding of the different types of bulbs available and which ones are of use. Most bulbs lean on the side of warm or cool and usually not well balanced.
Bulbs
When shopping for light bulbs it is common to find the Kelvin listed but not the Lumen. Why? Lumen is a measurement gathered based on how for you are from the source. They couldn't possibly tell you the Lumen unless they knew how far away you were standing from the source, or how large the room is, or how much reflected light or other factors. Instead, manufacturers list the wattage of the bulb, i.e., the output based on how much energy the bulb uses. The more energy it consumes the brighter the bulb. They will also list the temperature output of the bulb in Kelvin. Artists generally look for bulbs that are 4,500-5,500 Kelvin. This number range is what represents an emulation of natural light. Any higher a value and the light becomes too cool. Any lower a value and the light becomes too warm.
An artist must be aware of the many types of light bulbs and their varying degrees of cool and warm. Energy saving bulbs give-off a violet cast, some a greenish cast and so-on. There is perfectly balanced lighting available however, none of it can be found at Home Depot or your local hardware store. Please see my blog post which talks about what types and brands are available.
Light measurements
Two units used for measuring light output are the amount of light being emitted (Lumen) and its temperature (Kelvin).
Lumen is the measurement used to describe the total amount of light emitted by a source based on the distance you are from the source, i.e, how bright something is based on how far away you are from it.
Kelvin is used for measuring temperature (how hot the output source). White light exists (as manufactured bulbs describe) around 5,500 Kelvin.
Another consideration to artists regarding bulb technology is the color rendering index (CRI) which is important information when purchasing higher-end bulbs, balanced bulbs. CRI has a percentage measurement from 1 to 100. 100 is the value closest to white light, otherwise known as natural light or perfectly balanced light, which is not too warm and not too cool. When looking to purchase studio lighting that emulates this natural white light, it is not hard to find inexpensive fluorescent T8 tube type bulbs having a CRI of 98%. Please refer to my light your studio section for more information.
CRI is a scale of measurement used to describe a light source's ability to reproduce the colors of various objects faithfully in comparison with an ideal or natural light source.
Lumen and Kelvin influence each other and contribute to the overall perceived value of a source's temperature and total light output. Too little Lumen and the light will become dimmer and warmer, like a candle. And, the more the Kelvin the more the light will be perceived as being brighter and cooler. The Sun is very hot and very bright. It has major amounts of both Lumen and Kelvin—so the light is very bright and white. Compare this to a candle which is very dim and very warm. In other words, very low in Lumen and Kelvin.
As incandescent bulbs are being phased-out they are being replaced by energy efficient Compact Fluorescent Light (CFL) bulbs. Artists are discovering that CFL's have some use in their studios because of their availability, low price and the cooler light output compared to that of an incandescent. Yes, these bulbs are cooler than incandescent but they do still emanate a sometimes blue, violet, orange or greenish tinge. However, this bulb technology is quickly improving and won't be long before it can produce a more useful balanced (white) light.
Until CFL's are improved, artists are finding that the most balanced light comes from designer fluorescent tubes (T8 tubes, 32 watt, 98% CRI). They cost about $10 each and they provide a balanced white light and are also known to help alleviate symptoms created by Seasonal Affective Disorder (SAD). The T8 tube is the bulb I would choose if I had only one choice. They do a great job with brightening the entire studio without having to deal with direct lighting and they last for years. In addition to the T8's, I sometimes use a Halogen or an incandescent bulb to warm-up the studio by carefully bouncing the light off a wall or ceiling.
Candle light is warm and produces a small amount of light. Low in both Lumen and Kelvin means warm in nature. Using the charts below, try figuring out where camp fire light would fit or where blue propane torch light would fit.
These charts will give you a better understanding of the temperatures produced by natural and artificial light sources. Like the color wheel, an artist should have these basic charts engrained in the brain. Study the charts. Keep in mind these charts provide values in Kelvin, not Lumens.
When you look at light, hopefully now, you'll think in terms of its intensity and temperature.
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