Primary lights and backup lights
SEAC primary lights are used for diving in dark areas where the use of a flashlight is necessary. For example in the Netherlands, but also in caves or during night diving. They are mainly used in dark waters to create sufficient light. Often, in addition to a primary light, a backup light is included.
It may happen that during the dive something happens to the primary light and it stops functioning. It is therefore wise to always have a backup light with you to find your way back. Backup lights can also be used as primary lights in the tropics. Because of the clear water, you often have a lot of visibility and the moonlight penetrates the water, so you do not need such a strong light.