I think it's fun stuff. Those floodlamp holders will thread into PVC fittings that have 1/2" pipe thread. For example, "T" fittings commonly have a 1/2" threaded "outlet" (the side outlet). You could create a pole with one of those floodlamp holders every 4". (You don't have to glue the PVC together. Just cut a slot in the end of the pipe so it will collapse as it goes into the fitting. Then use a sheet metal screw to "pin" the pieces together. I.e., it's not something you have to make perfect and commit to, or throw it all away.).
You could make a square "fixture" to hang from the ceiling. They're not as easily to find (you might have to buy from an online pvc fitting place), but there is a 90-degree elbow fitting with a 1/2" pipe thread "side outlet". Use T's between the corners too.
You can get some other ideas
here. (<<link). The 2nd and 3rd articles would be the ones to see.
What I like about the phoenelic sockets (the ones that come with clamp-on reflectors) is that they're threaded on the socket end. A reflector can be used. That's a big deal with omnidirectional lights. But, with LED lightbulbs having that "base" at the bottom, with LED chips flush mounted, pointing in the same direction, a reflector won't do much.
There seems to be a trend for LED lightbulbs to have a plastic or glass "bulb" like the old incandescents (going down to the male thread; no "base" going halfway up). The LEDs are hung in the center of the round part like a "filament." That's a step backwards for growing. If that proves to be the new normal for lightbulbs, then the PAR38, 30, 20 (BR30, etc.) floodlights will be the thing to use. Their LEDs are flush mounted. And, they come with a reflector. You just have to cut/pry off the outer lens. And then, there's an inner lens covering the diodes:
You definitely want the LEDs mounted like that. That's the real strength of household LED lightbulbs. That directionality out of the box is a very big deal (compared to reflecting omni light, like a CFL or the new LED lightbulbs).
That one had no inner lens. (It's part of the outer lens.). This is an example showing the lens over the LED:
I just started looking at these recently. Cree makes one. The lens looks like it clips into slots in the side of the reflector. I haven't gotten into it yet. I want to experiment using it as a concentrated flood light
That outer lens pried off (I didn't have to cut it off). I drilled holes around the outer edge hoping that might make the focused light less focused/concentrated. But, not so broad as no lenses at all. I think no lenses would be better because they cause some absorption loss. Having nothing between the light and plant should be more efficient, more light reaching the plant. But, I used to use the original glass Cree LED floodlight and had good results. So, I want to give this one a shot. I think using something like this as top lighting (penetrating into the plant) and the unfocused (lenseless) light around the sides. Even if there is some loss due to the lenses, it would be easier to manage the lights (mounting, aiming fewer of them. It's a tradeoff that way. If you'e managing a dozen lightbulbs, that can be tedious. You might not mind some lens loss for the sake of simplicity.).
Anyway, my point was: if LED lightbulbs go retro back to "flimanets" (made of LEDs), then these flood lights be the only choice (from the local hardware store. I'm sure there are other E27 grow-light "bulb" choices. I saw
@BigCube using something with an E27 screw base and LEDs flush mounted so they point 90 degrees straight to the plant.). If that happened, the phoenelic sockets (that come with the clamp-on reflector) won't be as desirable (for the option using a reflector) because these flood lights already come with them. The only downside if things go this way is that the bulbs cost more (with the built-in reflector). LEDs have lumen deprecation. The bulbs should probably be replaced after 2000 hours. Particularly lights used in flower. Veg doesn't matter as much. Rotate the flower lights to veg.
I wouldn't discount using these in flower either. Even as sidelight to a "real" grow light, they make a difference. I've used them to
flower at 18-22w/sq ft with good results. (<<link). It would have been better at 30w/sq ft. That's still low compared to how many LED grow-light fixtures are used (50w/sq ft). But, using them to sidelight a traditional fixture would make a big difference. I think the value is getting light *close* to the plant for less inverse-square loss. Adding 40w around the side of a plant (four 10w 60w-equiv bulbs) would be like adding 80w to the top light. I might be exagerating. But, it's much better than adding light to the top. It makes better use of the watts.