All compact fluorescent lamps require a slight warm-up time for the electrical current to fully heat the cathodes and reach their full lumen output. When a bare spiral CFL is first switched on, it lights up with approximately 80% of its rated lumens, but it will heat up to its full brightness in about one minute. Premium CFLs, like Neolite CFLs, reach full brightness in only 30 seconds. Covered CFLs typically have longer warm-up times – up to three minutes – because they have amalgam.
Amalgam is a substance composed of mercury and other metals that increases the temperature at which mercury vaporizes inside the fluorescent tube and prevents the CFL from overheating. The precise combination of mercury and metals differs among manufacturers. Amalgam is used in CFLs that are enclosed in a cosmetic glass cover because the cover causes the temperature of the CFL to increase. As the temperature of the bulb increases, the gas pressure inside the fluorescent tube increases as well, which can decrease the CFL’s lumen output.
The amalgam prevents the lamp from overheating by increasing the temperature at which the mercury vaporizes from a solid state to a gaseous state. The amalgam allows mercury to vaporize at the higher operating temperature of the covered CFL instead of the lower operating temperature of the bare spiral CFL. This provides optimal performance with maximum light output.
However, the amalgam causes the lamp to have a slower warm-up time than bare spiral CFLs because it takes the covered CFL a longer period of time to reach the higher operating temperature that vaporizes all of the mercury to be able to create visible light. Typically, a CFL with amalgam will initially turn on at approximately 50% of its light output and take up to three minutes to fully heat up to its full rated lumen output.
Covered CFLs will also experience a slightly shorter life due to the extra heat. For example, many covered CFLs have an 8,000-hour life because the CFL is completely enclosed, whereas bare spiral CFLs, on average, have a rated life of 10,000 hours. As the CFL heats up due to its normal operation, the air around it heats up as well. Because it is inside the cover, there is nowhere for the hot air to escape. The extra heat puts some stress on the bulb, causing it to have a slightly shorter life than if it were a bare spiral CFL.
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