LRC publishes ASSIST recommendation on lamp dimming look and feel

June 5, 2013
The new publication recommends acceptable characteristics in minimum and maximum dimming levels and dead travel, but does not suggest a profile of light intensity changes relative to dimmer setting.

The Lighting Research Center (LRC) at Rensselaer Polytechnic Institute has released a new publication in the ASSIST (Alliance for Solid-State Illumination Systems and Technologies) series that recommends how lamps should dim regardless of type of light source. The recommendations are based on research into industry standards, experiments that gauge use expectations and preferences, and lab tests of lamps and dimming controls.

The "ASSIST recommends… Dimming: A technology-neutral definition" publication is available on the LRC website. The study was prompted by the fact that dimmable LED and compact fluorescent (CFL) lamps often perform differently from legacy sources, but is meant to apply to all types of light sources.

The LRC worked on the project for two years with the normal ASSIST goal of removing barriers that might impede the adoption of LED lighting. "The LRC and ASSIST's industry members are interested in understanding the technical problems impeding market acceptance of LED lighting, and dimming is one focus area," said Nadarajah Narendran, the director of research at the LRC and organizer of the ASSIST program. "By understanding the compatibility issues and what users want when they dim their lights, we can improve not only the dimming experience but also the likelihood that homeowners will permanently switch to energy-efficient LED lighting."

Results summary

The results of the research are quite simple. For now lamps should be dimmable down to at least 5% of the full lamp output, and that number should be reduced with maturation of LED dimming technology. Lamps should produce at least 90% of full output (relative to light produced when not connected to a dimmer) at the maximum dimmer setting.

The LRC also addresses dead travel on a dimmer when there is no response by the lamps at the top or bottom of the scale, and recommends a maximum of 10% at either the low or high ends. Flicker is also addressed, albeit through a reference to a prior ASSIST recommendation on flicker from 2012. The new publication requires an acceptability rating greater than zero based on the methodology described previously.

The new publication mentions but does not define either dimming profile or audible noise associated with dimmed LED lamps. The document acknowledges the importance of minimum audible noise relative to consumer acceptance but also said there are simply no available criteria or measurement methodologies to apply to the problem at present.

The publication also doesn't address profile — which is the relative change of light level based on the dimmer setting. The report does say that people generally prefer a profile based on a square law curve (documented in prior LRC research) that matches the logarithmic response of the human visual system. The document does specify monotonic operation, meaning that the lamp should never respond in an opposite manner from a change of a dimmer setting — it should never increase in brightness when the dimmer is adjusted down or vice versa.

ASSIST is an alliance that dates to 2002 between the LRC, researchers, manufacturers, and government agencies. The mission remains helping the lighting industry transition to energy-efficient lighting.