Light is the item that decides your yield, your electricity bill and the heat load in your room. It is also the one where the figures used in the trade are the most misleading. This step gives you the three quantities that really matter, and the one that changes everything compared with a vegetable crop: photoperiod.
Real watts, not marketing watts
A luminaire is judged on three figures, and the first one is not the one printed in large type on the box.
Real power is what is drawn at the socket, not an equivalent power rating nor a theoretical sum of diodes. PPF is the total flux of usable photons emitted by the luminaire. And efficacy, expressed in micromoles per joule, is the ratio of the two: it is what separates two luminaires of the same power, and it is what decides your bill.
At the scale of a room, a gap in efficacy adds up fast. On an installation running thousands of hours a year, one or two tenths of a micromole per joule represent sums that far exceed the difference in purchase price.
