The performance of both fluorescent tubes and compact fluorescent light bulbs deteriorates in ambient temperatures that rise above certain design parameters. CFLs are particularly affected. At high fixture and room temperatures, light output and color characteristics deteriorate. The reason has to do with mercury vapor pressure within the lamp, which depends on temperature.
Some fluorescent bulbs, most commonly CFLs, use a mercury amalgam to extend the optimal bulb operating temperature to higher values. Mercury amalgams are alloys of mercury and other metals. The amalgam stabilizes the mercury vapor pressure when bulb temperatures rise.
Amalgam fluorescent lamps achieve over 90% of light output over a wider temperature range than standard fluorescent. However, these lamps also take longer to reach full light output on start-up than standard fluorescent.
Amalgam is important for applications such as recessed downlights where heat can easily accumulate, particularly if the lights are on for a long period of time and the ambient room temperature is relatively high.
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