The U.S. Department of Energy (DOE) recently released a report as part of its CALiPER program (Commercially Available LED Product Evaluation and Reporting) aimed at identifying the best testing protocols for characterizing white color-tunable LED lighting. The study showed that testing these parameters effectively will mean substantial testing work on the part of the industry.
“In this case, determining a sufficient protocol required more extensive testing than would be feasible for widespread use,” the report summary said. “The increase in testing burden could potentially be mitigated by specifying a relatively brief measurement stabilization process between readings at different settings, rather than requiring a lengthy warmup period between readings.”
Eight white-tunable luminaires were tested at dozens of points covering the range of color tuning (correlated color temperature) and dimming (luminous intensity). The report focused on full-intensity measurements, which were typically at 11 color set points covering a range of correlated color temperatures (CCTs). The study found substantial variation in input power, lumen output, efficacy, and Duv (a characterization of chromaticity from the CIE 1960 standard) over the color-tuning range for many of the products, which would not be captured with only a few test points. The results show that future test procedures will likely require at least five to seven measurement points to provide a reasonable characterization.
The DOE study also found substantial variation in the way tunable color was achieved in this emerging lighting category. It restricted the study to luminaires intended for architectural lighting rather than entertainment lighting—specifically, troffers and downlights. “A key distinction is linear (produced by two color channels) versus nonlinear (produced by three or more color channels) white tuning. Linear tuning products cannot track the blackbody locus (i.e., they cannot maintain a constant Duv as CCT is adjusted), whereas the nonlinear tuning products were effective at following the blackbody locus. The importance of this distinction with regard to subjective impression requires further investigation.”
While efficacy and efficiency are always important considerations when it comes to LED lighting, the researchers pointed to tunable-color luminaires as a product category designed to address concerns apart from core efficacy.
“In most cases, color-tunable LED luminaires are currently not competitive with fixed-color products (of the same type) if efficacy is the prime criterion. However, color-tunable products may offer non-energy benefits, such as the ability to shift spectrum to support human circadian cycles, affect mood and alertness, or provide a visually dynamic environment. For the downlight products, the efficacy was substantially below the ENERGY STAR qualification threshold, but in appropriate applications where aesthetics, wellness, or occupant satisfaction is very important, color-tunable luminaires are capable replacements offering features not practically available with any other lighting technology.”
Here's the report: CALiPER Report 23: Photometric Testing of White-Tunable LED Luminaires