Why are Battery Powered Emergency Lights Not Possible?

The installation of emergency lighting in a facility can be expensive; for this reason, many look for ways to reduce the cost. One way that has been proposed by many, is to use battery powered emergency lights. Since emergency lights all contain batteries, this would seem like an obvious solution; but in reality, they won’t work.

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The batteries in emergency lights are there to power the light when the building power is lost. As such, they are selected to provide sufficient power for a minimum of 90 minutes, allowing sufficient opportunity for egress from the facility.

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Since that is the only time that the unit needs to provide lighting, it would seem that the batteries would be sufficient, without having to pay the cost of wring them into the building’s power grid.

How Emergency Lights Work

However, emergency lights aren’t wired into the building’s power to provide power when the building power is lost; instead, the wiring provides a signal to the emergency light, letting it know when building power is lost. Circuitry within the lighting unit then turns the light on, providing the necessary illumination. Without the connection to building power, the emergency light would have no way of knowing that power has been lost and that the light needs to turn on.

Emergency Lighting Technology

To base the operation of the light on a photoelectric sensor would be unrealistic as well, as the sensor would turn the emergency lights on every time the lights in the room would be turned off. This would be ineffective, as the light would go on at times when it wasn’t needed. Whatever batteries were used in such a case wouldn’t last more than a few days.

Having to turn the light on manually would also be ineffective as this would require the personnel in the area where the lighting is installed to be able to see, in order to turn on the light. If they could see well enough to turn on the light, they probably wouldn’t need the light in the first place.

Emergency Light Batteries

At the same time, being connected to the building power insures that there is a way to maintain the battery in the emergency light fully charged. Any type of battery is going to lose power over time. Not having a way of recharging the battery would mean that over time, the battery’s charge would reduce to the point where it wouldn’t be able to provide power to the light for the full 90 minutes required. The only practical safety net for this would be to constantly inspect the lights, checking the battery charge level and replacing them as needed.

Without the ability to automatically recharge the batteries in these units, any power loss, which would cause the illumination of these units, would require the replacement of the batteries in each and every emergency light. Ultimately, the labor and materials requirements for replacing the batteries would become much more than the cost of wiring and installation, to tie these units into the building’s power.