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Bonkers Blog November 2017

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20 November (Part 1) - More light relief!

LEDsYou can never be sure where one’s web jottings go so making things up is not a good idea, someone will soon pick you up on it.

Andrew Bashford would never have dreamed that his abuse of a Transport Research Laboratory report would reach the team who wrote it.

Bexley Council has been making things up about their LED street lamps. Brighter, safer and people love them so much they stop the Leader in the street to tell her.

Those claims amused a qualified lighting engineer and he emailed with a few facts. His message wasn’t intended for publication but he subsequently gave his permission so long as his comments were knocked into shape a bit. So with just a few tweaks to the presentation, this is what he says.

I am a Lighting Industry Federation Certified Engineer. The LIF is part of the Chartered Institution of Building Engineers and lighting has been my life’s work.

LED lights are not especially efficient, certainly not as efficient as Sodium lighting. The ones Bexley Council has removed would have generated 101 lumens per watt, the more orange variants which fell out of favour produced 177 lumens per watt.

An LED might provide 80 lumens per watt with the best of them getting nearer to 100 lumens so with current technology, if they are using half the power the very best LEDs will fall a little short of half the output of Sodium lights - the sort Bexley Council were using.

LEDs become a little more efficient at low temperatures.

The LEDs themselves are pretty bomb proof, they fail because the control gear dies.

The technology is improving all the time but it takes a while to reach the marketplace. If Bexley has not used the very latest technology I fear it might not be as reliable as they would hope with less than optimal light output.

Light spread is a big issue with LEDs. I designed the lighting for several oil rigs where Health & Safety is a major consideration and they have since been converted to LEDs. Because the light does not spread the number of lamps had to be increased. Bexley Council would need to increase the number of lamp posts by at least 50% for the street lighting to maintain the safety levels achieved by the Sodium lamps.

As it is now coverage is a lot less even if the LEDs had the same or even a higher lumen rating than their predecessors.

At home I try to balance output, outlay and efficiency. As such the only place you will find LEDs is in the fish tank as they highlight the colours on the fish and in the porch light and just one table lamp which are both there for their decorative effect. For where we actually need light I would not currently consider LEDs.

They look modern, but they’re not. Bexley Council does not know what they are doing or there would not be so many complaints, when I look out my window I find myself wondering if there’s been a power cut.

I have an email from Bexley Council dated 14th June 2017 which provides comparative data on the lamps, it was referring specifically to Townley Road so the bigger ones found on busier roads, not the tiddly thing that is at the end of my drive.

This is what it has to say about light output.

The light output values are as follows:-

LED Lumen output = 8,800 Lumens (SON/T Lumen Output = 18,000 Lumens)
LED Drive Current = 690mA (SON/T Drive Current = N/A)
LED Circuit Watts = 69W (SON/T Circuit Watts = 180W)

Without going into a Physics and Electronics lesson the LED is white light and is more efficient than any other light source.

Those figures confirm near enough the 101 lumens per watt stated by the lighting engineer but they claim 127 for the LED, well above what the engineer says the best will give. Maybe he will have something to say about that.

However nothing masks the fact that Bexley Council says the LEDs are providing only 48% of the light from a Sodium and you don’t have to be LIF Certified to see that they produce only a puddle of light on the road beneath.


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