By the nature of the device, an emergency light is designed to come on when the power goes out.
Every model, therefore, requires some sort of a battery or generator system that could provide electricity to the lights during a blackout. The earliest models were incandescent light bulbs which could dimly light an area during a blackout and perhaps provide enough light to solve the power problem or evacuate the building. It was quickly realized, however, that a more focused, brighter, and longer-lasting light was needed. The modern emergency floodlight provides a high-lumen, wide-coverage light that can illuminate an area quite well. Some lights are halogen, and provide a light source and intensity similar to that of an automobile headlight.