DOE Follow-up Study of MR16 Lamps Looks at Performance with Transformer and Dimmer Combinations

The U.S. Department of Energy published a follow-up study that looked at the photoelectric performance of the same set of 27 LED-based MR-16 lamps that they tested for the 2014 CALiPER Application Summary Report 22. The latest study used commercially available transformers and dimmers and laboratory power supplies to provide either AC or DC power.

The study points out that the MR16’s form factor and system requirements pose challenges for LEDs. According to the DOE, the small size of MR-16 lamps forces designers to face challenges and tradeoffs in terms of both testing and performance. Additionally, when installed, the pin-based MR16 lamps operate at 12V, which requires the inclusion of transformer in the system.

When a dimmer is added, all three electronic devices must be compatible. However, such integration often results in unwieldy compatibility tables and ultimately causes complications before, during, or after installation.

The new study hoped to find out whether or not characterization using laboratory power supplies instead of commercial transformers can lead to a misleading characterization of flicker and power quality performance.
The study also intended to examine the full range of possible performance for a given lamp model, based upon the overall system including a dimmer and transformer combination.

Notably, the DOE says that industry experts have done a very limited characterization of the impact of real-world system variations on energy efficiency. As with other CALiPER testing, the intention was not to determine the best-performing products but to compare the test results against established benchmarks and thresholds. The goal of the testing was also to focus additional analysis on identifying variation and trends in performance.The results of the just-released study can be found in CALiPER Report 22.1: Photoelectric Performance of LED MR16 Lamps. The study examined MR-16 performance in five different test scenarios:

  1. Electronic/ELV — Each lamp was tested with an electronic transformer chosen from the lamp’s compatibility list (if available), and an electronic low-voltage (ELV) dimmer. The testing hoped to find a specific system combination in which the lamp, transformer, and dimmer were all listed as compatible. However, limited available information often made this difficult.
  2. Electronic/INC — Each lamp model was tested with an electronic transformer and a typical incandescent dimmer. The transformer was listed as compatible with the dimmer.
  3. Magnetic/MLV — Each lamp model was tested with a typical magnetic transformer and a magnetic low-voltage (MLV) dimmer. The transformer and dimmer were considered compatible.
  4. AC Supply — Each lamp model was tested using a laboratory power supply delivering RMS (root-mean-square) 12V AC.
  5. DC Supply.

As with previous CALiPER photoelectric testing, the results revealed significant variation in the performance of commercially available LED-based MR16 lamps. The variation was found both within a given test scenario and across multiple test scenarios.

Scenario one demonstrated the value of manufacturer-provided compatibility recommendations. Lamps that provided compatibility recommendations for an ELV dimmer and an electronic transformer performed best when operated with compatible transformers and/or dimmers.
Also, the MR-16 lamps that were tested with the same transformer but a different dimmer revealed that, while transformer compatibility is paramount, the dimmer choice could still have an effect the performance of low-voltage products.

One important distinction from previous CALiPER photoelectric testing was that regardless of the scenario, none of the LED MR16 lamps exhibited dimming curves similar to those of the benchmark halogen lamps.

Testing of scenario two revealed the potential issue of installing LED MR16 lamps with a typical incandescent dimmer. The typical incandescent dimmer is commonly found in existing halogen MR16 installations together with a potentially unknown transformer. In scenario two, few of the lamps performed adequately with the use of a typical incandescent dimmer, and many exhibited highly erratic dimming behavior.

However, test scenario three found the magnetic transformer-based systems to be relatively stable. These systems eliminate the compatibility concerns of one electronic component from the system, but draw higher system power. The testing of scenario three also found that additional tradeoffs may include more dead travel and higher minimum dimming levels.

The testing included scenarios four and five to help understand the relevance of basic photometric testing (following LM-79) of low-voltage products.

The DOE noted that the study used a limited set of metrics for comparison, and suffered from equipment limitations and normalization procedures. However, the results show that while lamp power quality measurements are unlikely to represent the installed performance of the lighting system, flicker measurements with an AC power supply may still be informative. The study concluded that just testing with a DC power supply does not allow for evaluation of metrics such as flicker and dimming performance. The study stated examination of MR16 lamps with various combinations of transformers and dimmers can reveal such metrics.

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