Making a short dive to the back of the big room at Diepolder III on Wednesday, when right at 249' my 10 Watt primary light went out. Plenty of other light from the team, and backup deployment was instantaneous with no issues on exit. Upon surfacing and inspecting the light, I found that the cause of the failure was - user. Upon locking down of the canister lid, the positive feed coming from the battery had been pinched by the negative screw on the back of the switch, causing a short to develop once it cut through the insulation of the wire.