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I believe that is exactly what I said. Photon flux density actually is a measure of the rate of flow of light in a given period of time. It is measured in Lumens. In order to get a proper measurement, the distance from the source as well as the capture area must be included in the calculation. It is measured in Lumens per square meter and is actually a count of how many photons are hitting the target in a period of time. I believe I also mentioned spectrum with my more specific term, wavelength.
Also, published Flux Density rates of various light sources do not take into account the direction of the flow of photons, and the actual lumens/sqm that is hitting the plants has much to do with the reflectors and most importantly the distance from the source. With this in mind, a well designed T5 running very cool and being able to be very close to its target can actually be more efficient than a "hot" light that has to be many magnitude further away... again, I said this in a less wordy way up above.
I may be new to growing, but I know my science.
Emmie
Ok, I have a 6 light T5, and I'm getting ready to start flowering some of my harem. Put some of the ladies to work. I'm thinking of doing a four/two combination. AMF, I'm going to get four red bulbs, and starting with either a red/white/red/red/white/red, or red/red/white/white/red/red sequence. Give me a scientific opinion on that please. I think some white is needed for growth too during flowering, but just not as much. And what you are saying is making sense as far as lumens and yield per lumen/square ft.