Why Use Self-Powered Exit Signs?
Exit signs are intended to guide people to safety in an emergency.
What would happen if, during an emergency, the exit signs became invisible?
That could be disastrous.
Although electric exit signs exist, it is usually a better option for exit signs to be self-powered. This helps maintain illumination if the building loses power and can help buildings remain compliant with regulations.
Self-Powered Exit Sign Regulations
The National Fire Protection Association (NFPA) dictates the standards for the illumination of self-powered exit signs in the USA in the Life Safety Code. It sets out the following general standards:
- Every sign must be suitably illuminated by a reliable source of light. This permits photoluminescent, externally illuminated, or internally illuminated sources of lighting.
- Emergency lighting must be provided for at least 90 minutes if the building lighting fails.
- Provided emergency lighting must put out at least a 0.1 foot-candle, and on average should provide a 1 foot-candle.
To help you ensure compliance with these regulations, we have compiled a guide to the different types of self-powered exit signs.
Photoluminescent and Self-Luminous Exit Signs
Photoluminescent signs are exit signs that absorb light from the environment and then radiate that light. Usually, these signs are painted red or green. The paint absorbs the ambient light from the building’s normal lighting system. In the event of a power failure, the paint glows, illuminating the sign.
The NFPA dictates that if a photoluminescent sign is used, the sign must stay illuminated for at least 1.5 hours after the light source is removed. It also mandates that a specific light must be designated to charge that sign. LED, Fluorescent, sunlight
Photoluminescent signs include glow in the dark exit signs and are very similar to tritium self-luminous signs. A self-luminous sign contains internally sealed tritium gas as the illumination source. Tritium gas is safe and these signs usually stay illuminated for 10 to 20 years with little maintenance required.
The biggest advantage of photoluminescent and self-luminous exit signs is that there is no additional power source required. The biggest disadvantage of the photoluminescent option is that after an initial period of brightness, the sign slowly loses its illumination and is usually not illuminated after ninety minutes. The biggest disadvantage of the self-luminous option is that these signs require a much higher initial investment.
Internally Illuminated Exit Signs
Internally illuminated exit signs are signs that require no external light to shine on the sign for it to be visible. Internally illuminated exit signs usually consist of one or more LED light bulbs contained inside a plastic or aluminum housing. The light shines through a colored film to illuminate the word “EXIT”.
The self-powered version of these signs most often consists of a battery contained inside the casing. It is common for these signs to rely on the building’s power source during regular operation, which keeps the battery charged and the light shining. If the building’s power fails, the battery will power the light bulbs and keep the sign illuminated for at least 90 minutes.
These are also a very energy-efficient option, with the average self-powered LED signconsuming only 1.1W nominal power during regular operation.
Internally illuminated signs must be compliant with the “Standard for Emergency Lighting and Power Equipment” set out by the Underwriters Laboratory (UL) 924, which determines certain product safety standards in the USA.
Externally Illuminated Exit Signs
An externally illuminated exit sign refers to any exit sign that requires a source of illumination outside of the sign itself. The main difference between this sign type and the photoluminescent sign type is that a photoluminescent sign will not require a light source to shine on it during an emergency, and an externally illuminated sign will.
Externally illuminated signs can use LED, incandescent, or compact fluorescent light bulbs to illuminate the required exit signs. They operate by being connected to the building’s main source of power. While connected, the building’s power will charge the batteries so that in an emergency, the batteries will keep the lights on, should all other sources of power fail.
For all externally illuminated signs, the Life Safety Coderequires that light should be visible for at least five foot-candles from the surface of the exit sign, and there must be a contrast ratio of not less than five-tenths.
Therefore, the light source must be much stronger in externally illuminated sings than in internally illuminated signs in order to comply with these regulations. The light must be strong enough to travel a distance towards the sign and then travel at least another five foot-candles as it reflects off the sign. For this reason, externally illuminated signs are usually the least energy efficient option, however, all options should be compared for each individual case.
Interested in Using Self-Powered Exit Signs?
We can help you compare your options to keep your people safe.