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I decided to check my knowledge on the efficiency of grow lights. From https://aeradix.co.za/grow-light-efficiency/: PPFD is a measurement of light intensity within the PAR wavelengths and is measured in µmol/m2s1. The efficiency of a grow light on the other hand is measured in µmol/J. Sometimes written as umol/j, μmol/j, umolj-1 or PPF/W. Grow light efficiency is also referred to as photosynthetic photon efficiency/efficacy (PPE). Thus, µmol/J is the amount of micromoles of photons produced per joule of energy used. The power draw of a light is measured in watts and watts is the joules consumed per second (J/s). Therefore, if you know the wattage of a single light source and the Photosynthetic Photon Flux (PPF) value, then the efficiency of the light can be calculated. For example: 1 100 µmol/s and 500 W is (1 100 µmol/s) / (500 J/s) = 2.2 µmol/J. A PPE of 1.5 umol/J is considered efficient. Anything above 2.0 umol/J is considered very efficient. For comparison, many (high pressure sodium) HPS fixtures on the market have an efficiency of 1.3 umol/J or less, with some of the best HPS grow lights approaching 1.7 umol/J. The best ceramic metal halide (CMH) grow lights have an efficiency of just under 2.0 umol/J. HPS and CMH efficiencies will increase in the near future, but LED efficiencies will increase at a more rapid rate.