The selection of the luminaire and its placement in the room are governed by:
- What is the room temperature?
- What IP-class is required?
- Where are the chilled beams or conditioning units placed? Is the luminaire exposed to air currents?
- Should the luminaires be on continuously or are they switched on/off at specific intervals/days?
Open reflector luminaires are designed so that the maximum luminous flux is obtained at a normal room temperature of 25 °C. When this kind of luminaire is placed in a cold space the luminous flux and the ignition ability are affected. The lower luminous flux must be taken into consideration during light planning.
On the other hand, luminaires with a degree of protection equal to IP 44 and upwards can operate, from a luminous flux standpoint, better when placed in a colder environment as the light source’s ambient temperature is usually a little too high when the luminaire is at normal room temperature. In this situation, the luminous flux increases, up to a certain point, as the ambient temperature drops.
It is important to use the right ballast to ensure the luminaire also ignites at low temperatures. The temperature specifications vary for different manufacturers and ballast.
The T5 light source emits its maximum luminous flux at an ambient temperature (around the lamp) of 35 °C. The temperature around the light source is controlled by the design of the luminaire. For luminaires with a degree of protection equal to IP 44 and upwards the light source can heat the space around itself even when the ambient temperature around the actual luminaire is low. This is why T5 luminaires can work very well even in cold surroundings.
The T8 light source is slightly different compared to the T5. It has its maximum luminous flux at a lower temperature, 25 °C. Consequently, the T8 light source emits a higher luminous flux than T5 at certain, lower, ambient temperatures.
In some locations the use of thermo-lamps maybe required. Thermo-lamps have an extra outer glass that insulates (thermal principle). The disadvantage of these lamps is that they have a larger diameter, which can cause problems in some luminaires. Thermo-lamps are available in both T5 and T8 designs, though not in all outputs. Please refer to the light sources chapter.
Luminaires should not, if possible, be placed too close to chilled beams or air conditioning units. The cold air currents can have a very negative effect on the luminous flux. This also applies to enclosed luminaires or when using thermo-lamps.
Actual luminous flux
The graphs below show how the luminous flux is affected by ambient temperature for a number of typical industrial luminaires. The red curve indicates the luminous flux with no air movement and the blue indicates the flux with an air flow of 0.5 m/s. As a reference value the luminous flux at +25 °C with no air movement is used.
Text and order numbers in italics denote the light source.
The stated values are intended as a guide only and not an absolute value. Please factor in a good margin when designing.
LED in cold spaces
LEDs are also temperature sensitive but not in the same way as discharge lamps (fluorescent lamps). As a general guide the light flow and life expectance improves at lower temperatures. As such, LED’s are well suited to cold areas but the gear is normally rated for a minimum temperature of -20 °C (variations exist). When planning the lighting design, the files use the normal lumin outputs. If you would like information on the “cold” value output increases, please contact us for guidance.