The methods used for calculating economic lamp lives by Strange and Prais are examined. It is concluded that neither is completely sound and an alternative formula is developed. The results although differing in detail from those of Strange are broadly in accordance with his findings. The longer economic lives suggested by Prais cannot be justified. No support for any general change in the rated life of electric lamps comes from these figures, but it is suggested that it might be worth offering a long life lamp of relatively low wattage for domestic use. For commercial consumers no single lamp life is likely to cover the range of situations to be found in practice.
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