light sources bring out flesh tones and warmer colors, while
cooler sources enrich blues and greens. Regardless of CCT,
white light has a natural appearance if its color output lies along
the blackbody locus. If it deviates significantly from the locus,
it can appear either greenish or pinkish in tint. ANSI Standard
C78.377 designates maximum deviation recommended for LED
general lighting, which provides the basis of LED binning and
ensuring good color quality.
The above understanding of color—spectrum, hue and tint—
forms the basis of color-tuning LED technology.
Color-tunable product types
With LED technology, manufacturers have the ability to change
spectral output either as a factory setting or in response to a
program or external signal. This gives us three distinct type of
color-tunable LED lighting.
Full color tunable: These products allow a range of saturated colors as well as white-light CCTs based on RGB plus
amber or white LEDs. The manufacturer may add other colors.
White light is challenging for these systems, notably in regards
to color rendering.
Dim to warm: These products, when dimmed, automatically make CCT warmer to imitate incandescent or halogen
lamp dimming. They typically operate at 2,700– 3,000K, which
warms to as low as 1,800K during dimming.
Tunable white: These products—ordinarily luminaires—
emit white light at an adjustable range of CC Ts. They typically
combine separately controllable arrays of warm-white (
typically 2,700K) and cool-white (typically 5,000– 6,500K)
phosphor-coated LEDs. Relative dimming of these arrays
changes CCT while also allowing light-intensity control. The
A closer look at
White light appears natural if its color coordinates on the CIE
Color Space fall along the blackbody locus, shown above as
a black curve. Because deviation from the blackbody locus
can result in a tint to the light that can affect color rendering,
manufacturers design LEDs to emit light within tolerances
established by ANSI C78.377 for LED general lighting. These are
shown as green boxes around each CC T. Simply dimming arrays
of warm-cool LEDs produces a linear gamut between these two
color primaries. Area/triangular gamut control adds colors to
the warm-cool mix to fill out the spectral content, resulting in
nonlinear tuning that follows the blackbody locus.
Above: In “focus” mode, the lights are set at their highest intensity with a
cool shade, suitable for concentration tasks such as test taking. In “normal”
mode, the lights are set at standard intensity and neutral shade. In
“energy” mode, the lights are set at a high intensity level and very cool
shade to keep children alert during mornings and after lunch.