Some details on the 10W Solarc lamps and ballasts, from the Welch-Allyn site
Welch-Allyn Lamps
Three lamp styles available: lamps in a 6-degree or a 13-degree parabolic reflector, and a bare bulb.
Four ballasts available, differing in input voltage:
10.2 V (8-cell NiCD/NiMH)
12.0 V (8-cell Alkaline)
12.8-13.2V (10-cell NiCD/NiMH)
14.1-14.5V (11-cell NiCD/NiMH)
The $500 developers kit includes:
5 lamp/ballasts of any ONE lamp/ballast configuration (your choice)
OR
2 6-degree lamps
2 13-degree lamps
1 bare bulb
2 12 V ballasts
1 each of the other three ballast types
This assortment is the vendor's choice - you cannot spec your own assortment.
The ballasts are unregulated: lamp power dissipation is a linear function of input voltage.
The "Zip file containing circuits that can be used to condition electrical input to B10N Series of ballasts" contains four simple circuits to set the input voltage for the ballast:
A schottky diode to drop the voltage
A linear regulator to drop the voltage
A linear regulator used to set two different voltage/power levels
A linear regulator implementing a soft-start.
It appears that the only critical parameter is the voltage supplied to the ballast: it needs to be in the range specified for the ballast in order for the lamp power to be within spec. Lamp power should always be in the 8 - 11 W range.
Efficiency is 85%, so for a 10.2 V (8-cell NiXX)current drain would be 1.15 A, about 90 minutes for 1600 MAH NiMH AA cells.
Not bad for a 450 lumen device.
I am pretty impressed by my Surefire G2Z/P61 at 120 lumens...