Thursday, 02 October 2014
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LED is the answer

In answer to the observations by David Cutter, and the article ’Street-wise street light’ there is one element missing.

In answer to the observations by David Cutter (Letters, 7 May), and the article ’Street-wise street light’ (News, same issue) there is one element missing.

That is the government’s intention to encourage consumers to move to energy-efficient lighting, particularly fluorescent, in the home, while dispensing with filament light bulbs.

However, the major aspect ignored is power factor. With filament lamps, the power factor is notably closer to the ideal of 1, where the voltage and current are in phase. This means power stations have an easier task to supply electrical energy efficiently.

Introduce fluorescent lighting, and the phase shift between the supplied voltage and current becomes significant. Consequently, the power station has to run at a higher power output, as apparent power, due to the loss of a near perfect power factor when referring to filament light units.

In other words, the loss of electrical energy has been shifted rather than being solved. While the ideal power factor is 1, where the load appears to behave as a pure resistive load, some fluorescent lamps can have a power factor of only 0.3.

I am moving to LED lighting as this has significantly less power consumption for the same light output, while having a significantly longer life than both filament and fluorescent lamps, and produces a close match to daylight without any undesirable loss of a near perfect power factor.

It is, at the moment, the obvious method of reducing power consumption without causing a major power factor problem.

Andrew Porter

Principal circuit design engineer, Ultra Electronics


Readers' comments (5)

  • I just found your article and it verifies what I knew. However, I was testing some small 1.5 watt candlelabra base led lights and found them to have a power factor of .12 as measured on a KilaWatt meter. I was horrified to see this number, any ideas? Is it just some led bulbs like this? thanks

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  • My MEP department is working on testing several LED products to determine their actual performance. We have found mixed results regarding power factor and wattage from 2x the advertised wattage and 0.6 PF to advertised wattage and 0.86 PF. There is still a lot of development occurring. Testing is recommended prior to specifying.

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  • I am disapppointed to see power factor brought up again as if it negates all the claimed energy savings. It doesn't.

    Yes, if not corrected, it affects distribution losses adversely, and wires in buildings do have to be adequately sized, which might mean half their previous area and not a fifth of the previous area, even if the watttage is cut 5x. But no, it doesn't affect the direct energy use, which with CFLs is usually cut as claimed by the manufacturer; e.g., a 11 W lamp may replace a 60 W GLS lamp or occasionally 25 W T5 products could replace 150 W GLS lamps.

    If power factor is an issue, it is for electricity companies and manufacturers to resolve; we should never risk using it to dissuade consumers from taking action on CO2.

    AFAIK most commercial sector lighting already *is* power-factor corrected. With better regulation we could do the same with domestic sector lighting. If LEDs are being sold with incorrect claims on light output, well, that sounds like consumer fraud to me, so why doesn't the OFT act?

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  • Presumably the leds will only run on extra low voltage DC or possibly medium voltage DC depending on the number of chips and the series/parallel arrangement. So the PF is really influenced by the transformer / rectifier circuit to achieve the correct voltage DC.

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  • Medium voltage?? >1,000 DC. Dangerous in the home. I think someone has their wires crossed, so to speak. Yes, Power Factor must be corrected for efficiency but it is easily done by adding capacitance to the fluorescent units. Manufacturers generally use capacitors that are considerably too small to perform the correction due to cost considerations.

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