I did the LED replacement thing in a slightly different application -- relamping an old optical comparator for which the bulb was discontinued. (an optical comparator is used in machining to project a magnified image of the part in question on a screen using reflected light.) In this case, I needed a very bright (~50,000 foot-candle) tightly focussed (80mm
2) single-point light source with very even light distribution across the focal point of the projected beam. Grid array LEDs would not work -- while the light might appear even to the naked (and overwhelmed!) eye, the grid pattern quickly becomes apparent when magnified and projected.
I ended up using a Luminous Devices SST/R-90. The 90 refers to the maximum current of 9 amps at 100% duty cycle. Very bright. Can be used for street lighting. I am driving it with a commercial buck driver (the H6Flex by
http://www.taskled.com) at 6 amps, but someone who knows more than I about designing and building these things should be able to make their own driver.
One thing that was a bit of a surprise for me, personally: I always thought of LEDs as being a cool light source -- not meaning the colour temperature, but rather the operating temperature. However, these high-power LEDs kick out a lot of heat just and are easily burnt out just like a CPU if you do not dissipate it. Mine is soldered to a copper disk mounted to a copper bracket with heat-sink grease and THAT is mounted in a heavy cast aluminium shell and I still need a cooling fan. (One nice thing about the H6Flex -- it has a thermal sensor and can be programmed to degrade the current as the heat increases. I set mine to a conservative 50°C)
So, very bright single source white LED emitters are available out there (and in a variety of colour temperatures too). A good resource in this area is
http://www.candlepowerforums.com. Those flashlight guys are up on all the latest offerings and are making things that are so intense they could be classed as weapons!