This is what Abiqua said, "Lumens are often used in short form to compare or estimate the brightness, especially with white light.....they often are skewed by a number of factors and can be misleading, especially when trying to measure actual light the plant is receiving"
I probably have my head up my ass cause I thunk what I was saying is there are a lot of factors that come into play when it comes to big fancy city boy lights. Distance being one of those. Now I went ahead and added that there distance part myself. I should have got prescription from the teacher but fuck it! And you're right, it's not that light is attenuated, it's that it's "spread out more yonder like" as us hillbillies like to say. I kind of remember some formula for it but let's just say after a few too many Dead concerts... Maybe if I were to axe my daddy/uncle he might be able to splain that there Newton fella's law of universal gravitation thingamajig to me.
Here's a good one... Watt the Fuck!
Any light source, not just the bigfancypants' "ones"......
Dude, I might be the 1st person from my family to get a BS or higher degree in my family...but lets be absolutely clear of hillbilly...
My Family is from either the Appalachians [Cherokee] or the Ozarks...thats its....I am a running 200 year old joke
This "theory" is applied to any source of light, whether its a campfire, a lazer, an HID light, an LED light, a CFL light.....its ALL the same....its just that lots of terms are thrown out to confuse and AWE....
Blue is more efficient than red...if you have equal amounts of lumens in blue and red, in theory, the blue will have more useable plant light than the red beams....BUT you have to have data from the LIGHT SOURCE MANUFACTURER to square away most of this shit....
Go google
ppf
ppfd
photometric
radiometric
lumens
lux
CRI
No one can help you, but you, get a little better understanding of some of these concepts before stomping around in the forest with just a torch....