Shape of Things to Come

It's looking like the end of the sodium reign could be in sight. Light Emitting Diodes are now being developed for streetlighting applications and, whilst currently more expensive to purchase than discharge lamps, their extended lifespan and zero-maintenance design will soon make a powerful economic case for their adoption. Economies of scale in production should ensure the initial purchase prices come down, as well.

LED's will provide higher quality, gentler and yet more efficient public lighting. Halting the HPS proliferation and replacing sodium with these likely lads will save energy and reduce light-pollution, whilst giving a more welcoming feeling to public spaces. Remember; at optimal colour-temperature they won't need to be anything like as bright as sodium in order to do a better job. LED's suitable for streetlighting are now available in various colour-temperatures, from a visually-efficient blue-white to a "warm" yellow.

From the Philips website comes this example of an LED streetlight-pair, one of four now used to light a pedestrian area in the Dutch town of Ede. In this instance, each lumiere contains 6x 3 watt white diodes and 12x 1 watt amber diodes. The ratio of white to amber light then is 3/2. Philips make this fitting available in a range of colour-temperatures by varying the amber/white diode ratio. C.T.'s are available from 2700k to 4000k. The one shown is, I would assume, the "warmest" at 2700k. Despite my initial alarm at the presence of amber diodes, a C.T. of 2700k is actually pretty similar to that of a domestic tungsten lightbulb. Standard HPS typically has a colour temperature of 1800-2200k, which equates to dawn sunlight [or a peach melba] and Mercury Vapour has a C.T. of about 4000k, equating to silvery moonlight. Again, I must stress: cooler whites are more efficient than warm whites and may therefore be run at lower lumen levels with less glare.

For a more detailed look at the ongoing developments in LED technology, I refer you to patmullins.com