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LED Light Life-time and Ambient Temperature

The life and light output of an LED light bulb is largely determined by two factors

  1. The temperature of the LED chip or case
  2. The temperature of the LED driver/power supply

Therefore, both LED chip and driver temperature will be affected by the outside ambient temperature (TA). This is typically not a problem for residential applications where LED light bulbs are only used for a limited number of hours. However, in commercial applications or applications where the LED light bulb is constantly switched on the ambient temperature becomes important as any loss in LED life span will become more noticeable. 

The ambient temperature of the LED light bulb can be affected by the type of fixture used. Whether or not it permits convection currents up past the LED bulb to permit cooling or whether the LED is completely sealed into the roof space which can be much hotter than the room temperature. In turn, fully enclosed fixtures such as garden lights can increase the ambient temperature surrounding the LED and proportionately the LED chip and driver temperature.

Many old halogen downlights contain use heat cans to reduce the fire hazard caused by the old halogen downlight technology where surface temperatures reach 250°C. Unfortunately, depending on the design of the heat can, they can raise the ambient temperature around the LED light bulb, thereby again reducing the life of the LED light bulb and marginally reducing the light output. For LED light bulbs with internal drivers the reduction in life span can be worse as described further below, although as noted this reduction in life span will generally not be noticeable in residential applications with operating hours averaging only 3 hours per day. Most metal cans also do have venting and in such cases can be left in situ depending on the harshness of the environment and the thermal (heat) efficiency of the LED light bulb.

When installing a LED light bulb in a downlight fixture one must also be careful not to cover the back of the downlight with insulation. Although most halogen downlights will have the regulatory 20 cm surrounding space to any thermal insulation to eliminate fire danger. For LED lighting this distance can be reduced to as little as a few cm around the LED downlight fixture, thereby further improving ceiling insulation, as long as the LED is not covered and heat is permitted to rise from the LED it will be fine.
 

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