Prototype McLuxIII-PD with proto NexGen x2 constant current driver:

Note: The light got quite warm and was actually hot at around 20 minutes when the output took a drop. For preservation, the light was then switched to low output for some time to allow it to cool down to room temperature. When switched back to high level, it immediately jumped up to 1500+ lux but rapidly dropped down to 1200 lux where it continued to decline. It would appear that around 40 to 45 minutes of intermittant use would be available on high output from the single 123 cell. The lux output would also be higher with intermittant use due to thermal considerations. On the low level, there was no thermal issue to consider. The light was held in a clamp providing little thermal relief.