We’ve all experienced
it. When we look over the meat display at the supermarket, all the cuts are a mouth-watering
red. However, once in the cart, the meat is a different shade of red. Why? Because
the appearance of color depends on the light source. However, the lack of color
consistency with LEDs is a problem that a new lab at the National Institute of Standards
and Technology (NIST) in Boulder, Colo., is seeking to correct.
“[LEDs are] what we’ll likely use in the future to
light our houses and public places,” said NIST vision scientist Wendy Davis.
“Everyone wants light that appears natural and is pleasing to the eye, but
with LEDs, we’re not consistently there yet. LEDs offer a lot of advantages
over incandescent and fluorescent lighting, but they don’t always emit light
that looks ‘right.’ ”
A bank of assorted LEDs allows researchers at NIST to test the characteristics
of light sources. Courtesy of NIST.
To solve the dilemma, Davis and a team of physicists created the
NIST Spectrally Tunable Lighting Facility (STLF), a lab that is the only one of
its kind in the world, Davis said. “We can use it to create virtually any
light source spectrum we can dream up, and because of that, we can test out how
a light source would behave as far as object, color or any other properties.
“By doing this testing, we can really save manufacturers
the effort of having to produce the light source that may or may not behave as they
want.”
A process of combining
The STLF lab concentrates on the relationship between physical
measurements of light and human perception of light and color. To this end, the
researchers combine LEDs of different colors to produce an acceptable overall color.
In the lab, hundreds of LEDs cover the ceiling. Davis can activate
groups of them, adjusting their color levels to demonstrate the effect lighting
has on the appearance of food and furniture. “Here in our lab, we test how
light sources are used for general illumination, and how they appear to people,”
she said. “This is particularly important for LEDs because they have potential
for great energy savings over our current lighting technologies.”
Efforts like this are helping the researchers develop a way to
quantify how LEDs affect the colors of objects in ways meaningful to the lighting
industry. They currently are developing a measurement tool called the Color Quality
Scale to help manufacturers develop LEDs for general lighting.
“Because the light emitted by LEDs is different from the
light we get from other lighting technologies, the way that we measure color quality
doesn’t always work for them,” Davis said. “At this point, LED
manufacturers don’t have a reliable way to determine the color performance
of their products.
“If we don’t handle this issue now, it could create
big problems for future LED lighting products, because bad color means unhappy consumers.
We want to use measurement, which is a NIST specialty, to nip this problem in the
bud.
“Ultimately, the measure of light isn’t really about
numbers and instruments and math. It’s about people. We use lighting so much
throughout our lives, and it’s really become such an important part of our
society. So the measurements that we do here are really about making our lives better.”