Figure 5.9. Lamp efficacy and ambient temperature



Figure 5.10 shows how the frequency of supply voltage affects light output.

Frequencies of 30kHz improve light output by up to 10%. This is why the use of high frequency electronic ballasts is becoming popular. Additional benefits are the high frequency eliminates any irritating flicker, is better starting, and the ballasts are lighter. Different size and shape configurations are easy to arrange with the electronic components. These features are of particular benefit to aircraft, marine and emergency lighting applications.

Lumen Maintenance
Light output decreases as the fluorescent lamp ages.
Phosphors deteriorate and produce less light.
Blackening at the ends of the lamp blocks light.
Light output decreases even if the lamps do not burn out. See Figure 5.11.



Figure 5.11. Lumen maintenance over time.

Mean lumens is an American measure taken at 40% of rated lamp life. In UK lighting levels are based upon maintained illumination and it is necessary to determine the minimum lighting level in the installation when replacement of lamps is due, taking into account all possible reasons for deterioration. This is not a set figure and will vary according to the operating conditions at each location.