Proper performance of emergency light fixtures during power outages
Customers always ask DMF Lighting about the additions to the 2014 and 2017 National Electrical Code®. The code details regulations regarding emergency lighting circuits, specifically Directly Controlled Luminaires. The 2014 edition added the following:
700.24 Directly Controlled Luminaires. Where emergency illumination is provided by one or more directly controlled luminaires that respond to an external control input to bypass normal control upon loss of normal power, such luminaires and external bypass controls shall be individually listed for use in emergency systems.
In the 2017 edition, ARTICLE 700.2 Definitions added the following:
Luminaire, Directly Controlled. An emergency luminaire that has a control input for an integral dimming or switching function that drives the luminaire to full illumination upon loss of normal power.
There are published magazine articles, if not read carefully, that suggest any lighting fixture that has a 0-10Vdc or digital control input and is used in an emergency lighting circuit, must be qualified to UL924, Underwriters Laboratories, Standard For Safety – Emergency Lighting and Power Equipment.
The key to understanding the NEC additions is the phrase direct control. Authorities want to ensure that a light fixture used in an emergency circuit will perform appropriately under emergency conditions. So with normal power lost, how does the light fixture respond to the external signal controlling the light level? One example of an unacceptable response would be a control signal from a dimmer set to zero during normal power operation and in emergency power mode the light fixture responds with no light output. Thus, the updates above ensure that this sort of emergency response does not happen. A light fixture that detects switching from normal to emergency power must provide sufficient light so people can respond.
DMF Lighting provides EM – Emergency Lighting options with most of its light fixture housing types. These emergency light fixtures dim with triac/ELV, 0-10Vdc or more sophisticated digital signals. However, during emergency conditions the dimmer does not control the light output. UL924 qualified emergency LED drivers detect the loss of power and switch control to battery power in emergency conditions.