Lumens per Watt

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The efficacy of a light source is a ratio of the amount of light produced (in lumens, lm) to the electrical power consumed (in watts, W). This is the lm/W figure and it is useful for comparing efficacies of different light sources. For example your staple MR16 tungsten halogen from a few years back would have been around 15-20lm/W, a typical Xicato LED module we now use in the TTX2.70 for example can achieve up to 136lm/W. What this figure does not take into account is the effect of the power supply or driver on the efficacy of the light fitting as a whole, for that you need to consider the lumens per circuit watt.