I just bought two 1/2 watt led's for Farnel ( £1.14) and replaced the bulb in my old rear Wonderlight with them. The output seems about 3-4 time as much and the current is down to 30 milli amps 9 which gives something like 15 hours plus out of the rechargeable Nicads I use.... That were the last of the incandescent bulbs that I have on bike - all 4 lights are LED's