manufacturer may add other colors to provide good color fidelity and, potentially, a broader choice of color. Some tunable
white products are also capable of dim-to-warm operation.
The blackbody locus is represented as a curve on the CIE Color
Space; significant deviation can result in tint that affects color
rendering. The approach of relative dimming between warm and
cool LEDs to achieve tunable white lighting results in a linear
gamut. In other words, the extremes of warm and cool may be
on the blackbody locus, but the shades of white in between may
be tinted. This can work well if the CCT adjustment range is
small, though care should be taken when mixing these tunable
white products with fixed-CCT products, as users may notice a
difference in color between them during dimming.
For a wider range, some products offer an area or triangular
gamut approach by adding additional color LEDs. The added
colors extend the choice of CCTs and allow saturated colors
while fleshing out the light’s spectral content, resulting in nonlinear tuning that follows the blackbody locus.
Tunable white lighting is often achieved using an LED driver
and a dimmer. The devices may communicate using low-voltage
wiring (0–10V DC, DALI, DMX, proprietary) or wireless transmissions (Bluetooth, Wi-Fi, ZigBee, EnOcean, proprietary).
Special instructions are needed to dim the different LED color
arrays. The user interface sends these instructions to the driver
or a lighting controller that talks to the driver.
A basic approach for warm-cool gamut control is a dimming
control connected to two dimmable LED drivers each with its
own control output. In this case, CCT and intensity are directly
related, so it’s important to specify the levels of intensity to gain
the desired CCT.
For area gamut control, one control input is dedicated to
intensity and another to CCT. In this case, the driver must be
able to dynamically mix the output from two-plus primaries. A
user interface might include a slider for intensity and another
for CCT, which allows CCT to stay constant during dimming.
Manual controls include sliders, keypads and other approaches.
While lighting controls enable tunable-white lighting,
color control is a new application. Often, a dimming channel
is dedicated for CCT control. More sophisticated approaches
incorporate multichannel hybrid LED systems
white LEDs plus color
settings. The additional
colors fill in gaps or
weaknesses in the color
spectrum, resulting in very high color fidelity.
Color points can be moved off the blackbody locus to enrich
specific colors in finishes, art and merchandise. Spectra can
be programmed for circadian lighting schemes. These systems
typically use thermal and optical sensing and feedback to calibrate and maintain the same CCT across installed luminaires.
As the market develops, we may see even more capabilities
such as very long fades and color-based programming.
Many aspects of application are the same as when applying
standard dimming controls. The designer must know who will
be using the controls to ensure their location and level of complexity is appropriate for the user. The dimmer should offer
an appropriate dimming range, tune intensity or CCT as precisely as needed, provide appropriate transitions or smoothness
across the range (both intensity and CCT adjustment), and, if
needed, dim to off. The luminaire should respond to the control
signal at an appropriate speed. All devices should be compatible, and the dimmer and driver pairing should not produce
Take note of the dimmer and driver curves. The dimming
curve may be linear, meaning a slider moving halfway down
will result in a 50 percent dim level. Or it may be square law,
taking into account adaptation by the eye. For example, a 25
percent dim level appears to be about 50 percent of light output,
which is predictable using the square law. Matching dimmers
and drivers with the same or different dimming curves can produce different effects.
New dimension of control
Traditionally, lighting control was limited to intensity control
(dimming) and on/off (switching). LED technology enables
color output control as a new capability, which opens up a
broad range of new applications. We are just at the beginning
of this trend and what it can do, but familiarizing oneself with
the technology can open immediate opportunities.
The U.S. Department of Energy’s Solid-State Lighting Program published a CALiPER report and fundamentals guide for
color-tunable LED lighting. For more, visit
DILOUIE, L.C. is a journalist and educator specializing in the lighting
industry. Learn more at
Tunable white lighting allows manual or
automatic adjustment of a luminaire’s
shade of white light, which opens a wide
range of application possibilities.
to 80 percent
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