For those of us who like to make our own caving lights and who are handy with a soldering iron  it is worth noting that some Poundlands are selling  the GU10 LED  240v ?bulb?  ?these have an unscrewable front bezel revealing 3 LEDs on an alloy heat sink with individual focus lenses  ?further unscrewing allows this to be removed and disconnected from the small transformer circuit behind ? I have snipped the LED mounting plate to give a single LED and a double . So far I have mounted the single with focus lens  in an Oldham head shell using  epoxy putty and connected it to a Petzl helmet battery pack with 3 AA rechargeables (3.6V) and run it raw ? this gives a good light and it doesn?t seem to get hot (unlike the LEDs sold about 10 years ago) but probably will need a current limiting resistor to increase the life span  (but at 35p each that isn?t the end of the world )- I think there was an article in Descent a few years ago describing the calculation for the value of R but haven?t been able to find it so far ) .The other 2 I have expoxied and wired into the base of an old MES bulb so that it will screw into one of  the old style bulb mounting brackets and wired it via the voltage  circuit board from a ?1 LED garden light so that will run off a  2.5 v  9 amp hour NIMH helmet battery pack.  All this for ?2 ! and not relying on proprietary  chips or chargers  it is field repairable .