All the electricity used by a lamp burning inside a cold room turns into heat, and the refrigeration system has to remove that heat again. In other words, lighting is paid for twice: once at the lamp and once at the compressor. LED luminaires give 120–160 lumens of light per watt; they provide the same illumination with about half the power of old fluorescent and metal halide lamps. What is more, LEDs work more efficiently in the cold and last longer; fluorescent lamps, by contrast, are slow to light at −20 °C and their light output falls noticeably.
The lighting level is chosen by the work: 100–200 lux at floor level in rooms used only for storage, 200–300 lux in aisles where orders are picked and labels read, 300–500 lux in packing and processing areas. With LED this means an installed power of roughly 2–5 W per square metre in storage rooms. The luminaire must have at least IP65 protection (dust-tight, resistant to water jets) and be suitable for the temperature of the room; for frozen rooms, models with a driver approved for −30/−40 °C are selected.
In the layout the luminaires are placed above the aisles between the racks, at a height where they will not interrupt the evaporator’s air stream and will not be hit by a forklift mast. Cable penetrations through the panel are made with sealed cable glands and do not enter sloping from outside to inside; otherwise moisture travels in along the cable and forms ice. In food businesses a luminaire with a polycarbonate body that does not scatter fragments if broken is required. Lighting switched by a motion sensor or door switch greatly reduces the burning time and the heat load in rooms that are entered infrequently.
The safety side must not be overlooked: the light not being able to be switched off from outside while someone is inside, an illuminated switch beside the door, emergency lighting that comes on when the power fails and an illuminated alarm button for anyone trapped inside are vital equipment, especially in frozen rooms. Ultraviolet lamps are not for lighting but for reducing microbes and are assessed separately. The cooling load calculator includes lighting among the internal loads together with its daily burning time; reducing the hours the light stays on lowers this item directly.