Below is a short article I contributed to the January 2016 issue of tED Magazine, published by the National Association of Electrical Distributors (NAED). Reprinted with permission.

The U.S. Department of Energy’s CALiPER program has released Report 23: Photometric Testing of White-Tunable LED Luminaires, the first in a planned series on this nascent product category.

Color-tunable LED products include dim-to-warm, white-tunable and full-color-tunable products. Dim-to-warm products automatically reduce correlated color temperature (CCT) to achieve a warmer color appearance. White-tunable products, which may include a dim-to-warm feature, can be adjusted over a range of white-light CCT values. Full-color-tunable products can be adjusted both in terms of white-light CCT as well as a spectrum of saturated colors.

DOE decided to focus its efforts on white-tunable products. These products at a minimum mix warm- and cool-white phosphor-coated LEDs, with a linear CCT range achievable between these two primaries. Other colors may be added to increase flexibility of adjustment and produce non-linear relationship that follows the blackbody locus, enhancing color accuracy. The LEDs are generally controlled using 0-10V, DMX, DALI or proprietary protocols.

The study’s first primary goal was to understand the amount of testing required to characterize a white-tunable luminaire. Just as LED lighting challenged testing standards optimized around conventional lighting, color-tunable lighting challenges the new photometric standard designed to accommodate solid-state lighting. A single photometric test in accordance with IES-LM-79-08 isn’t enough to characterize the performance of a color-tunable product.

DOE tested eight white-tunable luminaires at dozens of points covering the range of color tuning (correlated color temperature, or CCT) as well as dimming (luminous intensity). DOE concluded a minimum of five to seven test points would be required to reasonably characterize a white-tunable LED luminaire. The methods and data produced in this initial investigation will inform future testing and analysis of the category. Ultimately, it may lead to a new standard method for manufacturers to express performance of color-tunable products.

The second primary role was to test and profile the performance of a sampling of white-tunable products. Eight white-tunable 2×2 troffers, surface-mounted luminaires and downlights were tested. The report focuses on the full-intensity measurements, typically taken at 11 color points covering a range of CCTs.

The results show substantial variation in input power, light output, efficacy (lumens/W) and Duv over the color-tuning range for many of the products. It is possible for manufacturers to maintain input power or light output, and some of the tested products did just that. Significant changes in efficacy at lower CCT values may result in a product that does not comply with thresholds for ENERGY STAR and DesignLights Consortium Qualified Products List criteria across at least some of the tuning range.

Additionally, white-tuning products with a linear relationship between two primaries tend to have greater efficacy and are less complicated, but they produce a range of Duv values as CCT is adjusted, which may produce a pinkish or greenish hue at various points and may not be acceptable to users. Further, some products exhibited noticeable color shift depending on dimming (luminous intensity).

Examples of linear and nonlinear white-light tuning. While the curve may vary across products, the main difference is linear products produce a range of chromaticities directly between two primaries, while nonlinear products add other primaries allowing mixes that approximately follow the black body locus. Image courtesy of U.S. Department of Energy.

Examples of linear and nonlinear white-light tuning. While the curve may vary across products, the main difference is linear products produce a range of chromaticities directly between two primaries, while nonlinear products add other primaries allowing mixes that approximately follow the black body locus. Image courtesy of U.S. Department of Energy.

The CALiPER report concludes: “White-tuning luminaires are still in their infancy, with plenty of room to mature. While the linear-tuning troffers offered high-enough efficacy to at least be considered against fixed-color products, they are still at a modest disadvantage versus the best competitors, and it remains to be seen if linear color tuning is accepted by the market place.”

Regarding downlights, the report adds: “On the other hand, the white-tuning downlights—linear and nonlinear tuning alike—are at a severe energy-efficiency disadvantage compared to fixed-color products, not even reaching the minimum criterion for ENERGY STAR qualification.”

DOE noted that engineering improvements could change this balance in the future, however, and that the competitiveness of these products is based on non-energy benefits that may be difficult to quantify.

To download the report, click here.