Is Low Voltage Lighting the same as Low Energy?

by Steve on May 31, 2009

Is Low Voltage Lighting the same as Low Energy?

Of course it’s not, but this is an informative article and worth a look.

This article has been reproduced with the kind permission of MyGreenLighting.co.uk

Find them at http://www.mygreenlighting.co.uk/info/low_voltage.html

Is low voltage the same as low energy?

No! It’s the watts that count, not the volts.

There is a common misconception that low voltage lighting systems are the same thing in terms of energy efficiency as low energy lighting systems. On this page we will try to explain why this is.

Measuring energy

Energy is measured in watts – your electricity bill probably shows how many kilowatts you have used. A kilowatt is 1000 watts.

Therefore, if you can produce a lot of light while using a small amount of watts you have a low energy light, and a cheaper electricity bill.

You probably know that low energy light bulbs have a small wattage rating and are often compared to an equivalent wattage. You might see that an 11w low energy bulb is the equivalent of a 60w normal bulb. This is only comparing the amount of light that is produced, it has nothing to do with the amount of energy consumed.

Volts, amps and watts

To show that a low voltage light is not a low energy light, we will compare these three lights:

  • 50w low voltage spot light
  • 50w mains voltage spot light
  • 9w low energy spot light.

All three examples will produce about the same amount of light, but only one will cost less to run.

You might remember from your school days that watts = volts x amps. Once we know this we can easily show that the maths confirms the number of watts used by each of the three example light:

  Volts
(The electric supply
connected to the light)
Amps
(watts divided
by volts)
Watts
(as described by
the product)
50w low voltage spot light 12 4.17 50
50w mains voltage spot light 240 0.21 50
9w low energy spot light 240 0.03 9

 

As you can see – the 240v 50w bulb uses exactly the same amount of watts (power) as the 12v 50w bulb.

But doesn’t it use less power because it’s running at 12 volts?

No – watts are watts. It doesn’t matter what the voltage is. We can show this more clearly by explaining about transformers:

Transformers

Low energy lighting such as the 9w bulb in our example will generally run at the full mains voltage, without requiring any change in the voltage.

Most low voltage lighting runs at 12 volts so unless you’re running it from a battery (e.g in your car) there has to be a transformer to reduce the mains electricity supply from 230 volts to 12 volts. Some light fittings have a transformer built into them, and sometimes a separate transformer is required.

Transforming volts and amps

When a transformer transforms a voltage it also transforms the available amount of amps – In the table above you can see that the 12v light uses a lot more amps then the mains voltage lights.

The available amps are transformed by the same ratio as volts but in the opposite direction, so if the voltage is reduced by 20 times (240v to 12v) the amps are increased by 20 times (0.21 to 4.2).

In our above example the voltage has been reduced by 20 times, so the amps have increased by 20 times, but the wattage is the same.

Additionally because the transformer efficiency will not be 100% (some energy is lost in the transformation) the 12v bulb might even more use more power than the 240v one, as the transformer will be ‘using’ some as well as the light.

Is low voltage the same as low energy?

No – it’s the watts that count, not the volts.

Make sure you have a low wattage lighting system to make sure you’re saving your wallet and the environment by using low energy lighting.

Thanks to www.MyGreenLighting.co.uk

Source:   http://www.mygreenlighting.co.uk/info/low_voltage.html

 

ElectriciansBlog.co.uk

 

 

 

{ 4 comments… read them below or add one }

admin June 29, 2009 at 21:23

Yes. Things are changing fast in the lighting world and it’s not easy to keep up with latest products. The EU Directive on Lamps will push things along and it’s our job to make our customers aware of the alternatives.

Andrew June 10, 2009 at 16:23

(Thanks for publishing our article!)

We’ve noticed quite a bit of variation in light output between different lamp manufacturers – despite whatever might be printed on the product packaging. It might be worth comparing a few different brands of lamp.

A narrow beam angle can also make the lamp appear brighter as the light is concentrated in a smaller area.

You could also consider a CFL solution – the new T2 type lamps are shockingly bright: http://www.mygreenlighting.co.uk/414.html

admin June 6, 2009 at 11:06

I was recently been told by a lighting designer that GU10 (230 v 50 watt) halogens have about half the light ouput of a 12v 50watt. Nothing will match the low voltage for punch but some of the new low energy GU10 13watt CFLs come close for light output. Try the non-dimmable Edison EDGU10/13/84 13watt CFLs. You could try to sell her the energy saving benefits.

NIgel June 6, 2009 at 08:04

Just installed some JCC Fire Rated GU10 50w 230v downlights for a customer. In the adjoining room she has some existing Low voltage 50w dowlights. Now she is not happy, because the new GU10 lights are noticably dimmer than the Low Volage in te next room.
Any ideas on how I can improve the light output to match the LV lights ?

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