Is there an LED Fallacy?

Everyone seems to believe that LED lighting is the answer to energy conservation in lighting. But do the facts match the publicity?


I’ve been hearing a lot about companies changing their lighting over to Light Emitting Diodes and how these electronic lights are going to save the world from climate change but I’m a sceptic and never trust what the salesman tells me, so I’ve done a little research.

I think the best way to measure the “efficiency” of lighting sources is to use the “luminous efficacy” which measures the visible light produced in relation to the energy used to produce it (measured in Lumens per Watt (lm/W)).

Manufacturers claim figures in the range 4.5-150 lm/W (I’ve heard reports of LEDs under laboratory conditions demonstrating figures of over 300 lm/W but I’ve also heard that the light was of such low intensity that it wasn’t visible to the human eye) and in comparison a candle (which we first used to light our caves and continued to be common even into the last century – and even now during power cuts or romantic evenings!) produces around 0.3 lm/W -so LEDs are massively better.


On the other hand candles aren’t common as routine lighting anymore so perhaps a better comparison might be the incandescent light bulb as invented by Thomas Edison early last century (yes I know about Joseph Swan and the fact that the “modern” light bulb using inert gas and tungsten filament is a much more sophisticated device than the carbon impregnated thread and vacuum original) which comes in at 5-18 lm/W a vast improvement on the candle but inferior to most LEDs.

Light bulb

On the other hand you can no longer buy a 100W bulb so how does the compact fluorescent compare? Well they are quoted as 46-75 lm/W so they are better than the worst of the LEDs (though half as efficient as the best) but at least twice as energy efficient as the old light bulb – hence the EU legislation outlawing the latter! 

So it is just possible that replacing a CFL with an LED might actually increase energy usage IF the LED is one of the lower performers (on the other hand the even longer life of the LED and quick start probably make it a good move anyway).

As you may know I’m much more comfortable in non-domestic settings so maybe comparison with fluorescent tubes is more applicable? Ignoring T12 and switchstart T8 tubes as obsolete (on the other hand Voltage reduction works well on them if they are in place) ; T8 ballasted come out at 80-100 lm/W and T5 70-104 lm/W -so it is possible to do a T8 replacement with T5 and lose efficiency!

But do remember the “dimming” ability of T5’s (as reported in an earlier blog) allows much better control regimes. So IF you are replacing T5/T8 tubes with LED your LED needs to produce over 104 lm/W if you are to be sure that it is to produce more light for less energy – do yours?

Moving to more Industrial lighting types I have heard of councils replacing SONs (Sodium Lights) for streetlighting with LED. Now as SONs have a range of 85-200 lm/W and LEDs are up to 150 lm/W is that a good idea? Well disregarding the benefits of the white light from the LED and its long life (cherrypickers are expensive) I think the advice is -CHECK THE ACTUAL FIGURES FOR THE LIGHTS in question!


(btb I’m sure any LED manufacturer reading this only sells LEDs that perform right at the top of the quoted range or even above it! I’ve also discounted the effects of heat generation on heating and airconditioning of the building and the effect of fitments/reflectors which can be significant if not exactly sexy) While researching this I came across an article reporting an LED that is 230% electrically efficient – now that is good !

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