(Application – Print Viewing)
There are a variety of ways to evaluate the quality of white light. One is Color Temperature, which is one of the parameters you can set for your display with TruHu andone which I discuss in a separate blog post. But color temperature doesn’t tell the whole story.
It is possible to get a more complete assessment of white light by looking at its Spectral Power Distribution (SPD), which is simply the spectral curve for a given light source. Below are some examples of SPDs for Daylight and a Fluorescent light. What’s notable is how “spiky” the fluorescent light is. These two light sources could have the same color temperature, but depending upon the contents of your viewing object / print, will not appear the same to your eye.
Color researchers have attempted to quantify the consistency of a light source across the entire visible spectrum – basically, how “non-spiky” the light is – and call this the Color Rendering Index (CRI). The maximum / best CRI value is 100. Here are some typical CRI values for common light sources:
- Sunlight – 100
- Tungsten – 100
- Viewing Booth Fluorescent – 95+
- LED – 80-90
- Typical Fluorescent – 80-87
Bottom line – if you are purchasing bulbs for viewing print, make sure they have a decent CRI, 90+.
