Category: Color

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.

A Challenge for LED Luminaires

Today I was at an LED “shootout” at the New York City office of Barbizon (special thanks to John Gebbe and Scott Hali).  We were looking at products that might be used in a specific application – that of lighting an auditorium or theatre.  The shootout was between 26 fixtures from 17 manufacturers, all installed at a height of 10′.

Architecturally, the designer is essentially lighting three conjoined rooms:  the orchestra, where the ceiling can be 35′ high or more; the balcony, where the ceiling can range from 12′ to 25′ because of the steep slope of the seating; under the balcony, where the ceiling may range from 12′ to 18′, again because of the slope of the seating.

The first part of the challenge is to find a set of fixtures that can provide even illumination in these three spaces, each one of which has a sloped floor and therefore a  varying throw distance.  The second part of the challenge is for all of the fixtures to dim simultaneously.  Unfortunately, I don’t think we saw success.  Here’s what we saw.

First, only one manufacturer had a product line for all three possible mounting conditions – pendant, surface, and recessed.  That manufacturer, though, didn’t have three beam spread and/or brightness options to meet the range of typical installation heights.

Second, LED manufacturing is maturing, but it’s not mature.  That means we still don’t have strong, industry-wide standards for things like color.  In many cases it was difficult to use fixtures from two or more manufacturers because the color of the light produced (visually evaluated, and measured in color temperature, peak wavelength and spectral content) clearly didn’t match.

Finally, getting fixtures from multiple manufacturers to dim simultaneously proved very difficult.  Each set of installed fixtures would need its own (perhaps custom) dimming curve just to get a close match, and identical performance seemed impossible.   The problem here is three-fold.  First, multiple control protocols would be required.  The fixtures demonstrated used line voltage dimming, three-wire dimming, 0-10v DC, and DMX protocols.  That’s not a deal breaker, but it is an unfortunate complication.  Second, some of the LED drivers produced unacceptable dips, flickering, or pulsing of the light as they dimmed.  Third, some of the LED drivers couldn’t make a smooth transition from darkness or light, or light to darkness.  We saw fixtures pop on and drop out, dim up nicely but not dim out well, and dim out well but pop on.  Eventually this might be as easy as working with incandescent lamps, but not yet.

The easy lesson was that, for now, the safest choice for smooth dimming from darkness to full light is still incandescent.  The color of the light from fixtures in all of the installation conditions will match, the dimming curves will be the same, and they’re easy to dim.

The complicated lesson was that it is absolutely essential to mock up the proposed lighting system, using the LEDs, drivers, control protocols, and dimming equipment that will be installed.  It’s the only way to be certain that the start and end of a show, when the house lights dim down and then back up, isn’t a light show of its own.