Abstract
Five different types of LED lamps were aged for 35 months at room temperature and for six months at the temperatures of 45℃ and 60℃. The lifetimes for the lamps were predicted from the luminous flux measurement results. The long-term tests show that early predictions of lifetime can be pessimistic. The results at higher temperatures show that ageing can be accelerated by modest heating. On the average, heating to 45℃ reduced the lifetime by a factor of 1.35 and heating to 60℃ by a factor of 2.36. An alternative accelerated method to test and analyse ageing is proposed. During the ageing of 35 months, the changes in correlated colour temperatures were smaller than 4.3%.
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