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Teacher, techie, daddy, nerd. Often all at the same time. Teacher of Computer Science at @utcplymouth and #dev for various individuals.

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Can an LED Really Be Green

Can an LED Really Be Green?

Published on 19th February 2018 by Simon

This article was originally written by my father, Dr Colin Pykett, a retired former chief scientist at a Ministry of Defence research laboratory. It was published in Physics World in July 2007.

No doubt we all own many items of electrical equipment that often sit on standby with a little red or green LED (light-emitting diode) advertising their presence. Yet how many of us actually know how much energy these devices are still consuming? Does it matter? Should we think about switching them off completely more often?

Recently I decided to look into the matter in more depth after a “green” pundit appeared on TV declaring that just one of these items would constitute around 20% of our total energy consumption if it was left on all the time, even in standby mode. This sounded implausible; so like any good physicist, I put it to the test. Direct measurement seemed necessary since manufacturers’ figures are often wildly inaccurate, when quoted at all. Armed with an AC milliammeter, I began measuring the current consumed from the mains by each of the offending items in my house.

Before going any further, let me caution you against undertaking this yourself unless you are absolutely sure that you know what you are doing – it is potentially a very dangerous enterprise. But because I survived the ordeal, I can now reveal that the biggest culprits were a large TV and a desktop PC, each drawing about 90 mA RMS, while lesser currents were drawn by a wireless Internet hub (48 mA), a DVD player (28 mA), a base-station for a cordless phone (24 mA), a CD player (20 mA) and a video recorder (20 mA). Adding everything up, the total standby current drawn in my home was 384 mA.

There are two issues to consider: power and energy consumption. Taking power first, on a 240 V RMS mains supply (yes, I checked this too!), the total power consumed by these items while on standby was just over 92 W – in other words, a little less than a 100 W bulb. I guess you might now be at the stage of emitting the odd yawn – 100 W, so what? But multiply this figure by the number of households in the UK (say 20 million) and you get a figure of about 2 GW, compared with a power output of about 1 GW from a large coal-fired power plant. This made me sit up and take a bit more notice of the problem. And my calculation does not even begin to include all the business premises, factories and the like with huge quantities of similar equipment. I leave you to estimate how many power stations are, as you read this, hammering away just to keep all these pretty little LEDs alight day and night across the land. This represents a waste of energy on a massive scale, with significant implications for greenhouse-gas emissions.

Quantifying the second issue of energy consumption, my domestic standby power of 92 W means that about 2.2 kWh of energy are consumed every day by the items mentioned. This is a little more than the energy that would be gobbled up by a one-bar electric fire left on for two hours every day whether you needed the heat or not. So, as with power, the energy figure cannot just be ignored. It is also instructive to look at it as a fraction of my total electricity consumption, which I estimated fairly accurately by looking back at my utility bills over the last five years. This turned out to be 9.2kWh per day on average, meaning that the fraction of my total electricity use consumed by items in standby mode is about 24%. I found this figure surprisingly high. Interestingly, it more or less tallied with the 20% bandied about by the pundit referred to earlier, though my analysis confirms that he had got his wires crossed when he insisted that each item in the list would account for this sort of figure.

In reality my household is not quite as wasteful as I might be implying because some items, such as the computer, are not left in standby mode all the time. Also our house has long since been vacated by the teenagers who otherwise would have inflated the problem massively (and other problems as well, but let’s not get drawn into that). However, these mitigating factors will not apply to many other households, implying that they waste even more energy than we do and in doing so pay out a lot more in terms of hard-earned cash.

The morals that can be drawn from this exercise focus on the manufacturers of consumer equipment at least as much as on the consumers themselves. Some of the items on my list simply must remain switched on – such as video recorders, which otherwise more or less instantly lose their memory of what channels they were tuned to, the time of day and so on. This is sloppy design in this day and age. A more insidious problem is that some items continue to draw current even when their front-panel LEDs indicate they have been switched off – at least one well-known Japanese manufacturer puts the on-off switch in the lowvoltage side of the internal power supply circuit rather than in the mains input circuit.

This applies to both my radio and CD player, which only stop drawing power when the external mains supply is physically disconnected. That these problems can be solved is illustrated by my MiniDisc player, which consumes negligible current when on standby, even when its tiny LED is illuminated. There seems to be room for stricter legislation here. So, next time you contemplate buying a piece of equipment that must be left in standby mode, you might reflect on whether its LED is really all that green, whichever colour it might actually be.