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New LED fixture with improved efficacy

Posted by bugbee on 13 Apr 2016 at 23:01 GMT

Bruce Bugbee and A.J. Both
We recently completed replicate, collaborative testing of a new white LED fixture from Fluence Bioengineering (model VYPRx PLUS). The efficacy came in at 2.05 micromoles per joule with flat plane integration at Utah State University, using a supply voltage to the lamp driver of 116 VAC. At Rutgers University, using an integrating sphere, we measured 2.02 to 2.05 micromoles per joule, depending on the supply voltage to the lamp driver of 120 or 277 VAC, respectively. The photon distribution from this fixture is broader than most LED fixtures, but more focused than HPS fixtures.
Although there are several claims of high efficacy LED fixtures for plant lighting applications, this is the first fixture we have tested with an efficacy higher than two micromoles per joule. The best previous efficacy we measured was 1.7 micromoles per joule.
[A note on the difference between efficiency and efficacy. The term efficiency is typically reserved for ratios that have the same units in the numerator and denominator, like watts per watt. Efficacy is the appropriate term when the units in the numerator and denominator are not the same, as in micromoles per joule.
When the units describing the ratio of the output divided by the input are the same, a percent efficiency can be calculated, and, theoretically, the ratio can go to 100 %.
When the units are different, 100 % efficiency does not make sense. It is not difficult to calculate the efficiency of a fixture in watts of output per watt of input; but as described in the article, plant growth is determined by moles of photons, not by watts of radiant energy. So it is appropriate to calculate fixture efficacy in micromoles per joule.
The term efficiency was used in this manuscript to refer to the ratio of micromoles per joule. While this is a useful descriptive term, it is not technically correct.]

Competing interests declared: Bruce Bugbee is a co-author of this article