A Close Look at LED MR16s
By James Brodrick, U.S. Department of Energy
The U.S. Department of Energy’s CALiPER program has released a new report on the photoelectric performance of LED MR16 lamps, which present unique driver design challenges and tradeoffs because of their small size and the fact that pin-based MR16s operate at 12V and thus require a transformer. A follow-up to a previous CALiPER report on the photometric performance of the same sample of 27 lamps, the new study focuses on performance variation for a given lamp model, based on the system to which it’s connected, as well as whether characterization using laboratory power supplies instead of commercial transformers can result in misleading flicker and power quality performance characterization.
Five different test scenarios were used, with substantial variation found in the performance of the LED MR16s both within a given scenario and across multiple scenarios. One difference from previous testing was that none of the LED MR16s, regardless of the scenario, had dimming curves that were similar to those of the benchmark halogens.
- In Scenario One (operation of each lamp model with an electronic transformer selected from the lamp’s compatibility list – if available – and an electronic low-voltage dimmer), lamps with manufacturer-provided compatibility recommendations performed best when operated with compatible transformers and/or dimmers. It was also found that, although transformer compatibility was paramount, the choice of dimmer could still have an effect on performance.
- In Scenario Two (operation of each lamp model with an electronic transformer and a typical incandescent dimmer with which the transformer was listed as compatible), few of the lamps performed adequately, and many showed highly erratic dimming behavior.
- Scenario Three (operation of each lamp model with a typical magnetic transformer and magnetic low-voltage dimmer that were considered inherently compatible with one another) demonstrated the relative predictably of magnetic transformer-based systems, which eliminate the compatibility concerns of one electronic component from the system but draw higher system power. This greater compatibility, however, is not without tradeoffs, such as lower system efficacy and possibly more dead travel and higher minimum dimming levels.
- The purpose of including Scenarios Four (operation of each lamp model using a laboratory power supply delivering root-mean-square 12V AC) and Five (operation of each lamp model using a laboratory power supply delivering 12V DC) was to help understand the relevance of basic photometric testing of low-voltage products. Due to equipment limitations and normalization procedures, only a limited set of metrics could be compared, but the results show that although laboratory lamp power-quality measurements are unlikely to represent their performance once installed in a lighting system, flicker measurements with an AC power supply may be informative (testing with a DC power supply doesn’t allow for evaluation of either metric).
For complete details, see the report.