Hogarthian Divers - DIR diving - Doing It Right - Diver

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1/ Stabilize the convulsing diver. Control her position in the water column by making physical contact (either with her person or a piece of equipment.) Do not ascend while she is in shock and convulsing.
2/ Do your best to hold the regulator in her mouth (certainly the gas she is breathing MAY be causing the convulsions, and the ideal action would be to have the stricken diver breathe from YOUR gas supply; however, breathing any gas is better than breathing water).

The light below is designed as a back-up light and is made from a single, milled piece of a very tough plastic called Delrin. Note that there is no switch as this is a common failure point. The light is switched on by turning the bezel.
The backup light is neatly clipped to the shoulder D-ring and lies in line with the webbing.

For open water dives is using two of them. For cave diving and wreck penetration I would use two of them as the consequences of a light failure are much more serious and one more backup in the dry suit pocket.