The Grow Light Intensity is a main factor that should be considered, this measurement is PPF (Photosynthetic Photon Flux). PPF is a measurement of the total amount of grow light produced by the LED or a light source per second. This is measured in micromole per second or umol/s
The most important and first thing that should be looked at is the PPF efficiency. The PPF efficiency is usually calculated by the PPF (umol/s) divided by the consumed power (watts). For example a LED with 1000umol/s that consumes 500W will have an efficacy of 1000/500= 2 PPF/W or umol/s.w. The higher the PPF per watt, the more efficient the light source for plant growth and maximum yield.
The coverage area of an LED can also be a driving factor to determining which LED grow light is best for the grower. However coverage area can be misleading at times if a recommended height of the LED is not provided. The coverage area should also be considered from the growers requirements, for example a growers might need a minimum of 200 PPFD (PPF/m^2). However a manufacturer’s coverage area might show coverage of up to 150PPF
A LED’s reliability and quality is also a great way to determine if the LED is best for the grower. The quality of the build as well as the components used can determine how long a LED unit can last. Durability is an advantages for LED over other grow lights, with LED that have been built with high standard material and components which have been through the correct production methods and quality control can last over 10 years.
PPF Efficacy Explained
1.5 umol/J is considered efficient. Anything above 2.0 umol/J is considered very efficient. For comparison, many 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 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. In 2014, the best LED grow lights had an efficiency around 1.7 umol/J, but nowadays, we are seeing efficiencies at 2.2 umol and above. As of this writing, the most efficient LED grow light we can find is around 2.87 umol/J !
Efficacy is why wattage does not matter for determining the light intensity of an LED grow light or any grow light. More efficient grow lights will emit more useful light while drawing fewer watts.
PAR efficacy may not be as important to some growers as other growers. Indoor farmers with a large operation should care about efficacy more than smaller growers since a difference of less than 1 umol/J will have a huge impact on their electric bill. For the average home grower, the cost difference between a semi-efficient and very efficient LED grow light may not be a huge factor, but as most growers DO care about their electricity bill, every watt being pulled from the wall is important.