Uncle Mort said:
I suspect in a dim and distant past on a diffferent forum I saw you posting instructions or your home-brew lights - if so, would you mind terribly reposting them?
Cheers, Mort
I think that was a chap called "rooster" who used to sell his own home brew light heads for about £15-20 and very nice they were to. I used an MR16 unit from the USA designed for cars (actually probably chinese in origin). It was about $8 for a pair mail order or about £2 each in todays money! It doesn't really matter, as long as the lamp is metal to cope with the heat.
Basically all you need is 12*cells of around 4500mAh with solder tags or you can buy a pack from batteryspace, a switch, some mains flex and a you can add a fuse for safety. Best to split them into 2*7.2V packs which are common radio control sizes for which it's easy to get chargers or ready made packs.
The magic efficiency for halogen comes from three factors that combine together:
-The Philips bulb has a special IR reflecting coating that boosts efficiency by about 40% - they claim - I'd say that's optimistic, but they are definitely better. As a bonus the internal build of these lamps is different (there is a large metal support on the burner) and this makes then very tough.
-The MR16 format is larger than the typical MR11 format of bike lights, the reflector is MUCH more efficient this size. This is a problem in all of those oh so neat little lights - the bulb itself obscures the tiny optics!
-Overvolting is MAGIC - 20% more voltage buys you 87% more light - and the light is much whiter too instead of the typical yellowish halogen. Now this does come at the cost of bulb life BUT domestic lamps are designed to work in enclosed fittings, the additional cooling in a metal fitting on a moving bike means this is no problem - I still have all the original bulbs working from 3 years ago.
Basically you get around 70% HID levels of efficiency (bike HIDs are not that efficient anyway as this is compromised by the small form factor) without the cost and the fragile eletronics. The bulb you want is Philips Masterline MR16 ES and the narrowest 8 degree beam (it has a good "be seen" halo) - it's important you get the right one!
I don't of course count the charger as I already had a suitable one for charging radio control model battery packs.
I personally don't think HID has much of a future in small applications like bike lighting because LED is already much more effecient and it only takes 3 emitters to match the amount of total light output these days. also you get none of the drawbacks such as the high-voltage electronics, fragility and limited bulb life.
References:
http://nordicgroup.us/s78/wattslumens.html
http://nordicgroup.us/s78/headlights.html