new outdoor Garage light project

So, finally the POS outdoor wall sconce light outside our front door died... was one of those POS BI-Pin CFL units.... not cry'n about its loss.

we bought one of the HD $35 units to replace it... picked one of the longer running demo units that HAD NOT failed or dimmed.
however, it doesn't have the throw the old unit did... so... wifey said "fix it"..... so i showed her some of the custom made units here on CPF, she fell in love with mds93's outdoor lights....
snatching the ball and running with it.... my design won't be as long. maybe 30" with 5 xml2 warm whites... perhaps 7... but not pushing it. i'm thinking 5 xml2 at 3A should be plenty.
going to mount them on a multifin'd heatsink (need to source yet)
Running a 50w line voltage driver (need to source as well)
motion sensor ( here's an issue, i have several but they use an SCR as opposed to a relay, so the power is rectified.... i think this is going to be an issue... any advice other then powering a relay?)

Debating on using lexan or pyrex as a front glass... this light will be exposed to FL sun in the evenings, but not until the last few hrs of the day.
Instead of the orig design, i'm going to compact the reflector from 5-6" down to a 3" tube. i want more flood than anything. i CAN up the # of LEDs if needed but i think 5KLms is plenty for our lil corner of earth. not worried about any power draw issues. whole light will be sealed except the back side of the heatsink.

so... at 30" long x5 xml2 at 3A (manf rec max), how thick does the main plate need to be, with (lets say 5 fins at 3")? (thermal mass transfer is NOT my forte.) i'd like some room for expansion as well.... say 7 xml2's
keep in mind this is FL, so at hottest, 100 Deg F ambient temp in the night time. light will only run for 5-10 mins average, with an occasional "Working on the car" time of an Hr.

and yes, Semiman, i welcome your input as well.

TY all... i'll be updating this thread with build pix and beamshots as it progresses.

as always with my builds, any and all comments/suggestions are welcome!

In my experience, acrylic (PMMA) is inherently more UV resistant than Lexan (PC).

Acrylic is way better for UV than polycarb. Outdoor lenses are almost exclusively PMMA. Even with UV inhibitor, polycarb is not as good.

5 XML2, 3A --- means about 15-20V at 3A. You can likely find drivers that do that, but you will have better luck, and better efficiency versus cost with higher voltage strings.

Not sure what directions the heatsinks are going to be. Always try to visualize airflow over a heat sink. Lots of LED lights, especially many of the early street lights out of Asia had somewhat useless fins on top in worst case conditions. It's late so not looking now, but there are flat plate heat sink calculators. XML's can run really hot before there life is seriously impacted. At the life you require and typical on times, die temps of 120-130C would still have almost no impact on # years of operation. Channel may be enough, just make sure wires and the like are good for 105C and fixture temp stays <90C.