CR4 Intstallation Guide - looks like nearly any 4" housing with at least 3-1/2" depth should work. Since the CR4 has the Edison socket on a pigtail, it can be adapted to fit nearly anything out there - you can even remove the socket mounting plate if necessary. Don't know how you're going to use the existing 5" housings though unless they are actually slightly less than 5", as the CR4 built-in trim is only 4-7/8" wide and the three metal tabs that keep it in place aren't designed to hold the lamp in place in a 5" wide housing. Maybe with a 4" cylindrical steel insert fashioned from a length of rigid clothes-dryer exhaust pipe?

The least problematic approach would be to use the Sylvania RT4 or retrofit 4" cans.

The Sylvania RT4 utilizes the torsion spring mechanism to hold the lamp in place (which is used by other manufacturers) unlike the Cree mechanism.

The CREE lamps on the other hand perform better than Sylvania (-quicker on response, greater dimming range, better CRI) and may be cheaper in some locales.
Making a metal insert is time consuming as
1. The insert has to be able to retain its shape even as the CR 4 is inserted. The seam needs to be riveted in order to hold.
2. The insert needs to be held in place inside the can using sheet metal screws.

Cree really needs a CR5

This is the video I was referring to:
http://www.youtube.com/watch?v=xdHwzTt-EQA

He's using the Sylvania's... I was under the impression that the cree's retrofit mount would work the just about the same. Guess it doesn't have the right clips/spring?

Sigh... I really want to use Cree!

Here is a link that might be useful: Youtube

All the CREE modules use the 3 prong mechanism to dig into the sides of the can.

has anyone tried the sylvania rt4 retrofit? i have the lightolier 5 inch cans and have watched the video. it looks like a good solution. i bought and returned the cree cr4+cr6 led replacement fixtures. the cr6 fits but looks too big, as the trim ring is 7.5 inches across. the cr4 looks much better but the fixture does not fit in the 5 inch can. it's too bad because the quality of the led light is lovely. i may go with the sylvania rt4 retrofit.

sendslim, I haven't tied the RT4, but the RT6 is quite nice. It dims well, and the 3000K version sold in Lowes is a nice white, without being too white. I ended up going with the Cree products, mainly for cost reasons.

having watched the youtube video provided to us by mje113, i decided to go ahead and purchase two sylvania rt4's to use as a test for retrofitting my 5 inch lightolier recessed fixtures. the good: the rt4 3000k light is a wonderful bright, white light. not too harsh but definitely whiter, with a noticeable increase in light output compared to the 50w philips halogena bulbs they replaced. the swap out was very easy and took just a minute or two to complete. they dim well with my existing dimmers. the bad: the fit is not completely seamless as the rt4 fits into, not over the existing lightolier baffle and trim ring. not too bad with my 10 foot ceilings. there is also a very slight(less than 1 second)delay before the light switches on. i suspect that when all the fixtures are swapped out the delay will not be noticeable. the bottom line: i'm very pleased with the quality of the light but may wait for sylvania's new rt5 fixture which is just about to hit the market before making my final purchase. cree has no plans, at this time, for a 5 inch retrofit.

Here is a link that might be useful: Sylvania RT5 five inch retrofit

It took me a while to get to it but I finally purchased a 4" ecosmart/cree fixture to try out on my 5" lightolier cans. Sure enough, just like the Sylvania lights, these snap right into the black baffle trim. You do still see a bit of the original trim, but as soon as I paint them the same color as the ceiling I think it'll be acceptable.

mje113, i'm delighted to hear that the 4" ecosmart/cree led fixtures work with the 5" lightolier cans. i had tried a retrofit earlier, before seeing the youtube trick of using the baffle trim piece to secure the new fixture. home depot's ecosmart 4" fixtures are very well priced in the boston area, well below the price of lowe's sylvanias...i'm going to give the 4" ecosmart/crees another look. tx for the update

i recently bought nineteen, 4 in. ecosmart/cree 9.5 watt led fixtures to update my 5 in. lightolier cans. they cost $22.93 each, plus an additional 15% discount for using my discover card to buy them online, with store pick up, during the holiday bonus period. sylvania has a 5 inch fixture but the only place i found them charged $62 apiece. in the end, i could not justify the additional cost to install a fixture so that the existing trim ring could be completely covered. the ecosmart/cree installation was a breeze but the three metal wings needed to be flattened slightly with a pliers to ensure a tight fit, as the new leds were snapped into the existing lightolier baffle trim pieces. the new leds are lovely, noticeably brighter, dim nicely and should have a positive effect on our electric bill. i am delight with the outcome.

fyi. i was told after i installed the 4 inch ecosmart/cree led fixtures into the existing 5 inch lightolier ceiling cans, that the addition of a socket extender would have allowed us to use the 6 inch ecosmart/cree leds from home depot. the 6 inch leds would have completely covered the lightolier trim ring, giving a sleeker more finished appearance. something to consider but too late for me. i'm done and happy and saving money every month.