What is the purpose of true underwater lights?

The purpose of true underwater lights is to withstand pressure at depth. These lights are specially designed to function effectively in the underwater environment, which includes dealing with high pressures that accumulate as you go deeper in the water. Unlike regular surface lights, underwater lights must be built to endure the intense external pressures of the water column, ensuring they remain functional and safe to use while diving. This capacity allows divers to effectively illuminate their surroundings without risking equipment failure due to the harsh conditions present underwater.

The other options, while they may have some relevance to lighting needs, do not specifically address the critical engineering aspect that defines true underwater lights. Saving battery life, providing warmth, and illuminating large areas, although important considerations, are secondary features and do not encapsulate the fundamental purpose of these lights.