The Best Light?

In class yesterday one of my students, thinking about a project she had recently completed, asked, “What’s the best light for a hair salon?”  I’m certain she was hoping I would tell her exactly what lamp technology and/or lamp style to use.  Of course, it’s not that simple.

So the class took a detour to talk about the important aspects of light in a hair salon.  We narrowed it down to two critical considerations – intensity and color rendering.  Intensity is important because the stylist needs to be able to see the details of a head of black hair as well as a head of blonde hair.  Intensity is relatively easy to achieve, and the designer has a wide range of lamp technologies, lamp shapes, and fixture types to choose from.  Finally, everyone intuitively understands how intensity affects vision.  If there’s not enough light one can’t see well enough to work.

Color Rendering is more complicated.  All of my students had heard of color rendering, but few of them understood its meaning or use.  Color rendering is the ability of a light source to enable us to see object colors.  For instance, a light source that produced no red light would do a terrible job of allowing us to judge red apples and we would say it has poor color rendering.  Color rendering is measured on the Color Rendering Index (CRI) which compares the light source being tested to incandescent light (for warm light) or to daylight (for cool light).  The higher the result, on a range that peaks at 100, the more a light source simulates incandescent or daylight in enabling us to see the colors of illuminated objects.

The best light source, then, is one that produces the desired intensity and has a high CRI.  Of course, there’s much, much more to color rendering and to the topic of color in light.  The color chapter in Designing Light is about 40 pages, and the IES DG-1 Color and Illumination looks like it will be about 100 pages.  It’s critical that lighting designers understand color because it has such a strong affect on people.  Color rendering is just one aspect.  Color also affects things such as our impressions and perception of a space, circadian rhythms, visual acuity, and the interior designer’s color palette.  Those are topics for another post.