Page 37 - Energize June 2021

TECHNICAL

A non-maintained emergency light will only activate in the event Self-contained emergency lighting
of a mains power failure and will also stay on for the minimum A self-contained emergency lighting luminaire is one which provides
emergency duration required. Non-maintained emergency lights are maintained or non-maintained emergency lighting and in which all
likely to be found in offices, shops and factories. the elements, such as the battery, the lamp, the control unit and the
test and monitoring facilities, where provided, are contained within
Luminaires the luminaire itself or within 1 m to it. The battery is kept in a stage
Emergency lighting can use standard lights and fittings, such as of charge by a charging circuit. Power supply to the emergency
tungsten halogen incandescent, compact fluorescent, fluorescent lighting depends on the type of lamp used.
and LED lamps, as well as purpose designed luminaires using LEDs.
All standard lamps require an AC supply to operate. Purpose built, In an AC powered self-contained unit the power supply would comprise:
non-standard LEDs operate from either an AC or DC supply. • AC/DC converter and battery charger
The flexibility and wide range of LED components available has • Battery
allowed the development of purpose-built LED emergency lighting • Inverter to supply AC from the battery if standard lamps are used
designs, which optimise the lumen output and the operating voltage. • Mains fail detection and changeover control unit.
LED lighting requires much simpler mains-interface electronics and
can be supplied directly from a centralised DC source. Development Typical circuits are shown in Figure 2.
of LED lighting systems has led to the use of DC power for lighting, The system operates as an offline UPS where the inverter is in
and this simplifies the emergency lighting system. The system may standby mode. For non-maintained units, the inverter is only used
use a centralised DC system for the whole building, or separate DC when the main power fails. For a maintained unit, the main supply is
system for each floor or work area. used when available.

Power sources for emergency lighting A DC powered self-contained unit. If the main supply is DC, self-
Power for emergency lighting is provided by batteries, which are contained units may not be required. A DC self-contained unit
kept in a state of charge by the main supply. The battery could be would comprise:
inside the luminaire housing (self-contained) or at a centrally located • Battery
battery system unit (CBS). • DC/DC converter if required
Battery capacity will decrease with time, depending on • Main supply failure detection unit
a number of factors. This means that a unit which meets the
operating time requirements at an installation will not do so at a later A separate battery charger is not required as the battery is charged
stage. Batteries are considered to have reached end of life when directly from the DC feed. In maintained units the changeover will
their capacity has fallen to 80% of the initial value and capacity be automatic as the battery is permanently connected across the
decreases rapidly after this point. It is good practice to oversize supply. In non-maintained units some form of electronic switching is
batteries by 25% to ensure that the operating time requirement can required to activate the light in the case of the DC supply fail. Figure
still be met at the battery’s end of life. 3 shows a typical system.

Maintained Non Maintained
Figure 2: AC powered self-contained emergency lighting unit

Maintained Non Maintained
Figure 3: DC self-contained units

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