I can see that you are keenly interested so just a bit of info I picked up. Obviously, if someone knows better feel free.
When Oldham developed the 'D' type LED headset they used an emitter (original Luxeon?) which was not very efficient but was capable of being focused into a very tight beam, as required in a working mine.
This LED outputs 90 lumens for a hit of 4 watts, same as a 4V X 1 amp bulb used in the GT headsets.
Therefore a battery capable of powering both for well over 12 hours was required, hence the L16. Lithium Ion, 16 ampere hours.
Obviously this kind of efficiency is a joke by modern standards but it was designed for a specific job.
I believe they have moved on from this and now produce something better which still meets the various standards.
Another point of interest is that to meet standards for working coal mines aluminium is right out of the equation, so you are stuck with plastic forever.
Again, I am told that the metal heatsink rim on the 'D2 type headset is cast nickel. Poor thermal conductivity but probably up to the job.
So come on, what can someone add to this?
My avatar is a poor likeness.