Yeah, I decided from the beginning that if I was going to design something, it was going to be ground-up. The only off the shelf parts are the components on the circuit boards and the optics - and even then, I'm not using a traditional Switch-Mode controller. I instead opted for a single DSP that will control the switch gates of all 8 supplies. In an LED light-bar like this, I'm breaking new ground, for sure. In fact, there are very few products in the world right now that use a DSP to control the SMPS of even a single LED - let alone 24 high power ones.
The comment about the pros making mistakes.. Trust me, I'm fully aware.. And disappointingly, I am one of the 'pros'.. I'm not really that upset about it - it happens. I'm helping another engineer right now with a product (commercial nature) that is still not working at Rev Q (Yep, ABCDEFGHIJKLMNOPQ) - and he's a very good engineer!
I'm going to be using three different optics. They're all the CUTE-3 optics from LEDiL, but I'll be using four of the narrow optics, two of the medium optics and two of the wide. This should give me a powerful throw and a ton of wide angle spill and cover everything in between. I'm expecting a long-reaching WALL of light. In the unit, the optics will be positioned, W-M-N-N-N-N-M-W.
Each triple is a series of the three emitters (roughly 9.9V Vf). The triples are individually driven using their own SMPS controlled by the DSP, so they're independent from each other. I could run every triple at a different current, if I wanted.
I have modeled it using the very thin FR-4 circuit board with tons of vias (which performs BETTER than an MCPCB), and I modeled the emitter itself using CREE's published thermal resistance through the package. At 3A per emitter (10W, roughly), I'm looking at a DeltaT of about 31C from the emitter to the enclosure (25C through the emitter package and 6C through the PCB). at my 100C trip-point, the emitters themselves will be running at about 131C. 100C is the trip-point, though, not the expected run-temperature. My study suggests that even on a very hot 90F day, the enclosure temp should not exceed about 78C - and this is worst case scenario with almost no air-movement. Just a little air-movement from wind or from driving would reduce that temperature drastically (10s of C). Real-world, normal use temperature of the enclosure is probably about 60-65C, meaning the emitters would be running 91-96C.
When talking about the enclosure to LED temp, you mentioned 5 or 10C. An MCPCB 'might' be able to maintain 5 or 10C from enclosure to LED Package, but remember the temp that matters isn't package - it's the actual diode junction. The XM-L has a 2.5C/W thermal resistance from Packge to Junction, so a MCPCB that could maintain 10C from Enclosure to Package would be able to maintain a 35C Delta from Enclosure to Junction when the emitter is running at 10 Watts. To get an XM-L to output 100% of it's rated Lumens, one would have to mount it on an MCPCB and then keep the MCPCB at minus 5 or 10C.
CREE rates the XM-L to operate at up to 150C Junction temperature, so with 31C Delta between enclosure and junction, I'm perfectly safe cutting off at 100C enclosure temp.
PPtk