No matter what grow lighting technology you might favor for your garden there are 4 basic performance factors to use when comparing between them:
Photosynthetic Photon Flux (PPF): the total number of photons the light emits.
Spectral Power Distribution (SPD): An SPD graph will show, In relative intensity, where those PPF photons are being emitted in the plants spectral (PAR) regions of 400-700 nm.
Watts at the Wall: This is the amount of actual power the light draws at the power outlet. It is not some phony made up number that LED mfg’s use to say their light is a 1000 watt light when it only draws 300 watts.
Percentage of Area Covered Losses (PACL); This is where the manufacturer should gives the buyer a recommended area coverage. Ideally that area coverage is going to be based on the manufacturer having tested their light by a 3rd party in a calibrated integrating sphere with intensity losses measured between the highest PPFD/LUX/LUMEN reading and the lowest PPFD/LUX/LUMEN reading. The lowest reading being at the outer edges of the recommended area coverage. The percentage of light intensity lost between the highest and lowest value is known as the Percentage of Area Coverage Loss or PACL. This value is given in a single percentage. The higher that percentage the worse the lights overall distribution is for the area coverage the manufacturer is recommending. For example if a mfg recommends their light for a 4 x 4 area and I have a PACL of 90% that means 10 uMol/m2-s at the highest point only generates 1 uMol/m2-s at the outside area coverage. This is unacceptable. The mfg needs to lower their area coverage recommendation so that the PACL falls to 50% or lower. If you don’t have a 3rd party test to go by with traditional photometrics or a PACL value that comes from those photometrics you are taking the mfg’s recommendation with no hard facts to support the area coverage.