Editing Emergency light (section)

==History==
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 bulb]]s 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.  Modern emergency [[High-intensity discharge lamp|floodlights]] provide a high-[[lumen (unit)|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]].

Early battery backup systems were huge, dwarfing the size of the lights for which they provided power.  The systems normally used [[lead acid battery|lead acid batteries]] to store a full 120 VDC charge.  For comparison, an [[automobile]] uses a single lead acid battery as part of the ignition system. Simple [[transistor]] or [[relay]] technology was used to switch on the lights and battery supply in the event of a power failure.  The size of these units, as well as the weight and cost, made them relatively rare installations.  As technology developed further, the voltage requirements for lights dropped, and subsequently the size of the batteries was reduced as well.  Modern lights are only as large as the bulbs themselves - the battery fits quite well in the base of the fixture.