5
3.12 Ambient and operating temperatures
In outdoor applications a natural air circulation around the luminaire is assumed, which gives a cooling effect of about 10 ºC.The same luminaire with an indoor ambient temperature limit of 25 ºC, will in practice have an outdoor ambient temperature limit of 35 ºC. If for outdoor luminaires an ambient temperature ta is given, it refers to the outdoor situation.
Special lamps, luminaires and electrical circuits have been developed for use in hot, cold, humid or potentially explosive environments. Amalgam lamps - and to a lesser extent also
However, where the decrease in light output and luminous efficacy can be tolerated, and provided proper measures are taken to prevent overheating of the circuitry, tube wall temperatures of up to about 90 ºC are acceptable.
The use of properly ventilated luminaires will, in most environments, obviate any heat problems.An air stream through the luminaire is an effective way of removing the heat generated by the lamp and ballast.
Fig. 129. Influence of temperature increase on lamp current (I), lamp voltage (V), lamp power (P) and luminous flux (Φ) for a 40 W fluorescent lamp on inductive and capacitive ballasts.
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120 |
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100 |
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80 |
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60 |
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40 |
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20 |
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0 |
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t (˚C)
3 
13
Effects of mains voltage fluctuations
The lamp voltage of a fluorescent lamp mainly depends on the lamp construction (length and diameter) and the gas filling. It hardly changes as a consequence of voltage variations in the mains, which means that fluctuations of the mains supply must be compensated for by the ballast.An increasing mains voltage results in a higher ballast current, as the impedance of the ballast is nearly constant (see section 5.1.2: Stabilisation).As the ballast current equals the lamp current, the power in the lamp and so the light output of the lamp increases at rising mains voltage.
Supplies with wide mains voltage deviations will lead to considerable deviations in luminous flux. Deviations of less than 5 per cent in conjunction with the normal ballast will keep the values within acceptable limits.The lumen level will not show fluctuations of more than 10 per cent.When the mains voltage constantly differs more than 5 per cent from the ballast rated voltage, the appropriate ballast should be applied.
136
