also a more even spread of light,
I think that's underappreciated. I think any time watts can be spread around the plant (different angles/coverage, fewer shadows), an efficiency is created (which you don't get putting that same number of watts directly above the plant). The more they can be spread out, or broken into smaller fixtures and placed at differing angles... I think that's low-hanging fruit.
I think a lot it has to do with distance. Putting all the watts on top (and especially into a single, compact fixture) means you have to keep the fixture higher. If a person has 400w on top: if they can split that into four 100w fixtures, and (for example) keep it 8" instead of 16" above the canopy, that's
four times the amount of light reaching the plant. Split it up further: have four 80w fixtures on top, and put the remaining 80w around the side, and you can have that sidelighting extremely close (2"). Say: eight 8-10w lightbulbs, two in each corner.
It's a tradeoff. If you had a roomful of 10 plants, it would be a full-time job fine tuning the lighting around each plant. But, for the typical 2x4 or 4x4 tent, it's not bad.
People squeeze the utmost efficiency out of the lastest COB or driver. I think that stuff is miniscule compared to the gains from spreading light around the plant, more even coverage.
A few years ago SMD5630(?) corncob lightbulbs were very efficient. (They may still be.). But, you could get them in low wattage and with a platic shell over the LED tower. They came with bayonett mount, the socket for which is very small. I had the idea to insert a dozen of those into the canopy (like a scene from Clockwork Orange). It sounds nuts. But, when you think about the inverse square... That would be like 40 watt laying on the leaves, all around the plant, with just 1/2" to 2" distance. The way the light becomes 25% less each time you double the distance... that 40w would be *enormous* compared to delivering it from the top, in a typical "UFO" fixture (at that time).
Enormous! Even if the UFO was 2" from the top of the plant, most of the light didn't reach plant material until 8-14" further down. That's *exponential* loss compared to laying light directly on the leaves (like a "light spa.").
I'm a big believer in that. Today you can get strip lighting that's encased in plastic. (IP67, whatever the rating is for that). Imagine having "light sticks" that you just push into the plant. (Make them double-sided, maybe triple sided). But, skewers that you push into the plant. Light it from every angle, from the inside out, and outside in. I bet you could flower a plant like that with just 12w/sq ft. Some amazingly small amount of power. Just because of how close the light is.
