Underwater, you can stow it out of the way in your BC pocket for when you go over the wall or peer deep under a ledge. As a back-up, the SL4 provides plenty of illumination to finish your dive. The eLED® circuitry provides relatively constant brightness throughout most of the life of the batteries. As the batteries are nearly depleted the brightness of the LED falls sharply, but does not go out as happens with classical filament lamps. This brightness will persist for several days. Valuable for emergency situations. The SL4 eLED® operates more efficiently and produces more light when when it is cool. Underwater, the SL4 eLED® burns brighter for almost half of the battery life, due to the unique way that heat is conducted away from the LED. Great for day diving or as a back up for night diving. Call 1-866-890-3483 to order.