Originally Posted by starry night
Jim, What LED brands do you know of that require at least 12 volts for full illumination?
I've seen demonstrations at the IA show and several local expos/shows that show 4 or 5 different brands of LED fixtures all lined up in a row, hooked up to a power supply with a dial on it, similar to the one below. And when the dial started to get turned down a little below 12, some of the fixtures would start to fade. Once it got below 11, you'd see them fade more. Below 10 and most of them were over half of the full illumination. At 9 most of them were off or so faded they didn't really illuminate much of anything.
I have a Protek DC Power Supply Model #3006B. I use it for testing fixtures like that. I just now did a test on an FX Luminaire JubileBijou that I had out in my garage (see photo below). Once I got down to about 11.3, I could start to see the light output flicker (probably the internal voltage regulator adjusting) and I could see output decrease a little. Once I got to 10.5 then it really began to fade from that point on. Once I was under 10 it faded by about half.
I've seen this at varying degrees with different fixtures. I should probably buy one of every brand they sell locally and document the point at which they all start to fade. But I'm not trying to start an argument here. Maybe it's 12v, maybe it's 11. My only point is they do all start to fade or go off at a certain point. Some brands stay at full power for much lower voltage than others. And if you aren't paying attention to what point the fixtures you install start to fade, and just daisy chain the entire system without really bothering to check this, you're may find yourself in trouble with some LED fixtures out on the market. In those cases, it probably would be a good idea to continue using the hub system. In the case with FX, I could notice a big difference between 12v and 10.5. So that's a pretty small range. If you're using a transformer that only had a 12v tap, you'd have to be very careful.
Now if you're using multi-tap transformers and starting with 15v, then you have a pretty big range to work with. You can daisy chain for much further. But if not, it is something you still have to consider.
I'll buy some other fixtures and see what I get with the others. I was pretty sure I saw some start to fade at just under 12. But I could be wrong.