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    The Efficacy Argument - LED Vs. Traditional Lighting Sources


    There has been a bit of controversy about the true efficiency of LED vs conventional lighting.

    Some traditional lighting sources such as fluorescents, metal halide and high pressure sodium bulbs appear to have similar efficacy to certain LED modules or packages.

    However LEDs will typically outperform conventional lighting and one of the main areas of argument is troffer fixtures commonly seen in commercial office spaces.

    The fluorescent tube in troffers emits light in a much broader beam, and because it’s mounted in a fixture that doesn't direct all the light down to where it’s needed, there are losses which occur, reducing the amount of usable light.

    This is defined as the light output ratio, or LOR which describes the light that gets lost from the luminaire.

    A typical flourescent ceiling troffer may have a light output ratio of just 0.5 which means that 50% of the total output from the tubes is wasted or lost.

    On the other hand, a LED tube with a 120° beam, will have a light output ratio 40% better than a fluorescent.

    Fluorescent tube fixture manufacturers often incorporate complex reflectors into the fixture to reduce the light lost, but still there is no comparison to the performance of the LED tube.

    Similarly, metal halide and high pressure sodium bulbs can specify higher efficacy than some LEDs, but losses occur because these specialised bulbs emit light over a full 360°.

    Another factor in the efficacy argument is the losses with LEDs. Recently we produced an article about LED lighting leader Cree’s new XP-L LED that can emit 200 lumens per watt. This is quite high, but the additional factors that affect the output of LED luminaires are losses through heat, which will reduce output the hotter the LED gets, optical losses which are formed by the use of lenses and reflectors or covers that reduce the light emitting from a fixture, and the additional electrical consumption from the power supply. Once you add these up, a LED chip which emits 100 lumens per watt may be reduced to 70 or less.

    In the case of the Cree XP-L, 200lm/W may reduce down to 125, but this is a huge step ahead of the efficiency of traditional lighting sources.

    The future of LED lighting technology is unstoppable. As efficiencies increase over time, new designs will replace the old - completely.