lightening the load?

The possibilities for ‘green technologies’ such as Light Emitting Diodes (LEDs) to deliver energy/carbon saving benefits are evident.

According to DEFRA[1] the average UK home contains approximately 25 light sources, which is not such a large number if you think about a modern kitchen having multiple down-lights. In the ‘good old days’ of the 60W incandescent bulb, the peak lighting load for this average property would have been 1500W. If we maintain a hypothetical like for like replacement with LEDs then this max load (if you are inclined to leave all the lights on) would fall to 300W (assuming a 12W LED equivalent). According to the DEFRA estimate this can be extrapolated to the 750 million lamps ‘actively in service’, meaning that by 2020 around 19.2 terawatt hours (1.92 × 10¹³ watt hours) will be allocated to domestic lighting in the UK (DEFRA 2009).  This is not an insignificant number of zeros given the carbon intensity of coal based electricity is 915 gCO₂/kWh, and a single coal fired power station such as at Aberthaw (near Cardiff) is capable of generating around 1.5 gigawatts.

Of course the fraction of this max load is dependent on many factors such as lighting controls, user behavior, natural light availability, luminous efficacy (lumens per watt) and luminaire service life, all of which influence whether the energy efficiency benefits are realized. For the integration of LEDs into general lighting applications, the most significant factor is the rebound effect. This cheaper to run more functionally flexible technology might make us more inclined to leave the lights on, or decide to illuminate things which ordinarily we would not (evident in most night time city skylines). Ultimately the positioning of LED lighting in the low carbon economy is dependent on not loosing sight of its evolutionary drivers, to deliver environmental benefits.