LED Wattage Equivalency Ratings Don't Tell the Whole Story
We now stock a number of LED bulbs in the directional bulb categories, such as LED MR16 bulbs or LED PAR30 lamps, that offer wattage equivalency ratings right on the packaging. Supposedly, this makes it easy for the consumer to compare LED light bulbs to the halogen bulbs they are looking to replace. What we've found, through direct comparison using the good old eyeball test, is that these ratings based on mathematical testing don't give an entirely accurate representation of real world performance.
The equivalency ratings are based on a test done for ENERGY STAR qualification using the Center Beam Intensity Benchmark Tool. Essentially, this tool is designed to provide a minimum center beam candlepower (the brightest location of the entire beam, located in the center of the directional light pattern and measured in candelas) that the LED bulb must meet or exceed when compared to a halogen bulb of the same type and with an identical beam angle. The problem of using this test alone to determine the equivalency rating is twofold.
In our opinion, the first problem is that nowhere does the test take into account the overall light output of the LED bulb (measured in lumens) as compared to the overall light output of the halogen bulb. This is a measurement that is completed on all LED light bulbs going through ENERGY STAR testing and is readily available. In most situations, total lumen output gives a more accurate representation of how bright a consumer will perceive the light to be when comparing it to a halogen bulb. The differences between the comparable wattage equivalency using lumens versus the Center Beam Intensity test can be as much as 25-30 watts! For instance, we've tried LED MR-16 bulbs with packages claiming 25 watt equivalency in our homes and found them to appear as bright as the 50 watt halogen bulbs they are replacing. That's because the lumen output of the two bulbs is very comparable but the center beam intensity is not. This leads to us to the second problem with the equivalency ratings, the test is inherently flawed.
LED bulbs do not generate light in the same manner as halogen bulbs. Halogen MR-16 and PAR bulbs use an omnidirectional filament, located in the center of the lamp, and a reflector to focus the light. Due to this design, the center beam is significantly brighter than the light just off center. On the other hand, LED chips are inherently directional and don't require reflectors to refocus or direct the light. So, even though they mimic the shape of traditional halogen bulbs, they don't produce or emit light in the same way. Many times there are multiple LED chips used, none of which are placed directly in the center of the bulb. This makes it nearly impossible for the LED bulb to achieve the center beam intensity of a halogen bulb without needing to have a much higher overall light output than the equivalent wattage would actually call for.
The conclusion? Our prediction is that as the LED lighting market develops further the current test for equivalency may be revised or modified. We suggest taking the equivalency ratings into consideration along with several other factors such as lumen output, color temperature, beam angle, and intended use. Lighting can be very subjective and the equivalency rating should not be used as the "end-all, be-all" of comparison tests.