By Steve Bush (click on image to expand)
The city of Pittsburgh is replacing all of its streetlights, and a friend drew my attention to a report from the University of Pittsburgh on life cycle and energy costs of street lighting, including with LEDs.
The report is a year old now, but still valid as it assumes efficiencies of up to 90 lm/W for lighting LEDs – still a reasonable figure.
It concludes that LED lighting is the best, but induction lighting – where induction fields energise a gas mixture in a sealed glass cell – comes a close second.
In fact, LEDs only win because they are still becoming more efficient, while induction sources are mature.
Low pressure sodium lighting – the almost monochromatic yellow lighting used in the UK – which delivers 300 lm/W – is sadly omitted.
I suppose this is not surprising as it is not at all common in the US where energy has traditionally cheaper than in the UK and less efficient, but whiter, high-pressure sodium lighting has dominated.
Page 47 includes an excellent graph which compares the efficiency of light sources from the year 1850 until the era of lighting LEDs.
If I have understood the references, this graph comes from Azevedo and Morgan, F, The Transition to Solid-State Lighting, proceedings of the IEEE, 2009.
Click on the image, above right, to see the full scale graph.