Yes and no. Nothing is 100% reflective and/or efficient. But you can thumb eyeball simply by definition of ppfd. Radiometric energy per square meter pretty much says it all. If you have a light with total output of 800 umols/s in 1m² then your ppfd average is 800 umols/s/m². What you actually measure can vary some by several different variables, and will probably be less because you will definitely lose some photons to those variables. But that is pretty much what you have to work with.
Personally, I feel this downloading apps and measuring is a waste of time. As long as you buy a light capable of hitting the target dli you should be in good shape. From there becomes an issue of figuring out what you can and can’t do with it. Runnning too high means you are bouncing photons off of walls unnecessarily. And running too close could mean burning your plants or limiting vertical growth. What works this grow may not with different plants in the next grow.
I definitely get it, im just trying to figure it out without actually burning my plants
I guess I could just use the Ppfd numbers from chart and assume, for at least a few grows i hope , that it’s accurate to my light. I would hope they used a better meter than I have. Unfortunately, they’re only measured at 100% I wonder if the numbers divided by 2 would represent 50%…? (On the sf4000 I can only control intensity with dimmer knob) It’s also measured in a 4x4 area, I’m 5x5. I doubt I could subtract the equivalent of 9sq" and go with those numbers
I definitely believe there’s optimal intensities for different stages of growth and of course strain, so I’d like some kind of baseline to work from. 3rd grow with gorilla glue 1st with Northern lights… here we go!! They’re about 2" and under t5. So I’m safe for awhile! Wish me luck!!
In a perfect world, customers would have demanded ppf of spider farmer fixtures disclosed prior to buying to them. They are pretty quick to make big efficiency claims, but where is the data to back them up? I don’t blame them though, the community hasn’t compelled them to release sphere data. You have industry leaders trying to set a standard by which grow lights are measured on a level playing field, and then you have a bunch of scabs ripping off their ideas, r&d, and designs. You would figure that as a group, growers could force their hand into providing same information as property they’re basically stealing. Or maybe not, because it hasn’t happened yet.
When you increase/decrease dimmer the output isn’t linear to dimmer knob. The leds become more efficient as current and temp fall. If you look at efficiency on ppf per watt scale, expect something around 10% increase in efficiency with 50% reduction in power. So if 100% power is equal to 100% light, then 50% power should be around 60% light.
I just checked my SF4000 with the new app on my iPhone.
Put white paper over the camera and try again. I had low DLI without any paper on my phone. I covered the camera with white paper and my DLI went up to where I wanted it.
, that it’s accurate to my light. I would hope they used a better meter than I have. Unfortunately, they’re only measured at 100% I wonder if the numbers divided by 2 would represent 50%…? (On the sf4000 I can only control intensity with dimmer knob) It’s also measured in a 4x4 area, I’m 5x5. I doubt I could subtract the equivalent of 9sq" and go with those numbers 
here we go!! They’re about 2" and under t5. So I’m safe for awhile! Wish me luck!!
Android 