In the event of an emergency, a power outage can cause the building's regular lighting to fail. Lack of visibility during an emergency evacuation is extremely unsafe and increases the risk of occupants being unable to evacuate safely. However, emergency lighting is unaffected during a power outage. These systems can ensure continued visibility throughout the premises and therefore ensure a safer evacuation.

Emergency lighting is crucial for protecting schools, hospitals and care homes. They also provide visibility for construction sites that have employees working through the night.

Any area of a building where a loss of light can increase danger will require emergency lighting. Stairwells and corridors require illumination to protect people from panicking and causing themselves or others harm during an emergency. Escape routes also require emergency lighting to direct building occupants to safety quickly and efficiently. Additionally, public areas that constantly use lower lighting, such as cinemas or bars, will require emergency lighting to guide people to exits and bathrooms.

Building sites particularly require illumination to help the workers operate safely at night. Without sufficient lighting scaffolding and construction sites can become fall or trip hazards. Emergency lighting should be placed in these areas to provide illumination and prevent accidents.

The lux of emergency lighting will vary depending on the location that needs illumination.

• Escape routes must have a minimum illumination of 1 lux along their centerline at floor level.

• Open spaces should be lit to at least 0.5 lux at floor level.

• Fire assembly points require a minimum lighting level of 1 lux.

• Rooms with specialised medical equipment for treatments should be illuminated to at least 50 lux.

• Kitchens require a lighting level of no less than 15 lux.

• Fire control equipment must be lit to a minimum of 15 lux.

• First aid rooms should have a lighting level of at least 15 lux.

Once activated the emergency lights will stay illuminated for three hours. This allows building occupants enough time to calmly and safely evacuate the area. This also provides respondents enough time to be alerted, to arrive and to help people evacuate by using the visibility of the lights. However, emergency lighting only needs to stay on for three hours if there are still people in the building. If all building occupants have been safely evacuated the emergency lights may be turned off after an hour.

Typically, emergency lights must have 50% of full power to be available within 5 seconds. The power should then increase to 100% within 60 seconds. However, in high-risk environments where hazards are imminent, full emergency lighting must activate within 0.5 seconds.