Replacing Halogen Spotlights with LED Bulbs

When we moved into our new house, the developers had decided to light almost the entire house with halogen spot lights.  Initially I didn’t pay too much attention to this, until after the first winter I was looking at the electricity bill.

Since I didn’t think we using more than our previous house, I did some quick back of an envelope calculation and results were quite eye-opening.

The house had 48 50W spot-lights and 3 20W down-lights. (When I came to replace them, I discovered that most lights were MR11s, each running off its own transformer also.) There were a few GU10 bulbs also.

My gut-feeling was that this was probably quite expensive to run, however I didn’t have the figures, so I did some rough calculations.

Now of course all the lights weren’t on all the time, but with us using some rooms longer and leaving other lights on to illuminate the stairs and landing, it still meant that we were using between 25-30 lights even if we were just using one room and leaving the stairs lit.

The most expensive time is over the winter months (October-April), so my calculation split the lights into two zones (high-use & low-use) and broke down the hours by month.

The winter months showed:

  • 30 lights for 5 hours
  • 10 lights used for 1 hour over this period
  • 8 lights were on intermittently – so I didn’t include these as I felt there would be minimal impact

This gave a usage of 1704 kwH (kilo watt hours) which on my tariff of 9.1pence per kWh meant about £155 in lighting over the winter months on a fairly conservative estimate.

Plugging in fewer hours over the summer months (3 and 1 respectively) brought the figure up to around £220 per year for the lighting.


The year one savings made the initial decision pretty easy, but rather than replace everything in one go, I did a few rooms at a time to get a feel for what the replacement bulbs would look like, and the type of light they gave.

Looking at suppliers, a replacement LED bulb rated from 4~5 watts was the equivalent of a 50W halogen. , This meant that each bulb would use about a tenth of the power of halogen it was replacing.

Bulbs cost from about £6 up for a 5 watt bulb, so the upfront costs of replacing all the bulbs would be £300 up.

However, having split the usages into high/low usage for the initial analysis, it was easy to target the expensive bulbs and leave the others until later.

UPDATE October 15, 2013 I’ve just fixed my electricity for another year & the unit price has gone up by 2p. This new price increased the savings from around £200/year to £250/year.

As noted, LED bulbs are more expensive (from £6 upwards depending on the brand and retailer), so replacing around 30 bulbs meant my lighting bills would be flat for year 1, (split between energy consumption and unit cost), with the costs being realised after the first year. If I replaced all the MR11 with individual replacement transformers, then the cost of each fitting would be about £10.  Replacing the existing fitting with a GU10 meant just replacing the transformer with a bulb fitting at about 40p per fitting, meaning each fitting would cost around £7 to replace.

Other factors to consider are the fact that LED lights have a MTBF > 50000 hours, whereas halogens seem to fall in the 2000 to 3000 hours MTBF range.

It’s possible to get very cheap halogen bulbs, but as I was paying around £1.50~£2 per bulb, I could expect to replace around 15 bulbs (which would work out at about £24~£30 ) for the lifetime of a LED bulb.

Some words on the calculations

Why are my calculations so “rough & ready”? For several reasons: estimating the hours used.  I discarded rooms we didn’t use as often. Having children/teenagers means lights will be left on in empty rooms. We’re not in the house the whole time (holidays etc).  In the summer months a lot less lighting is used, so I just cut these months out.

MTBF figures are hard to verify (I have no idea if I’m going to get the 50000+ hours of bright usable illumination from the bulbs). The fittings need to be factored in also. I kept the bathroom and kitchen bulbs as low voltage (12v) bulbs, so these cost a bit more individually.)

There are on-line calculators you can use to get an idea of the savings you could see. (I used calculators on and, but there are many others.)

I took the results from several of these as the upper limit of possible savings as the assumptions are based on number of bulbs & hours per day, assuming all bulbs are on for the number of hours given which isn’t the case (& for the yearly figures, they don’t reduce the lighting in summer)  Still they provide a good ready-reckoner estimate.

Other Factors to consider

The Temperature of the light.  There are currently three main light temperatures

  • Warm
  • Cold
  • Daylight

The warm colour is good for domestic settings. These are closest in colour to the halogen bulbs I was replacing.

Cold appears to be a much harsher light.  Probably more intended for industrial type applications. The light is more like a fluorescent bulb.  If you’re replacing lights in a work, shop or (home) office environment, these could be worth considering.

The daylight gives a brighter light with a result like natural light. I like this in the kitchen. I didn’t find as many suppliers offering these bulbs.

Beam angle

Halogen bulbs give quite a wide spread. When looking at LED bulbs, the bean angle goes from around 45° (or even less) to around 120°.  If you are replacing ceiling fitted bulbs and you have too narrow a beam, the room will have noticeably darker patches as the spread from the lights will not overlap sufficiently to give an even spread of light.

If you’re replacing single bulbs that are only highlighting a smaller area (maybe for reading), the choice of beams can let you tailor your light more precisely.

Dimmable bulbs

I wasn’t replacing lights on a dimmer, but there are now plenty of LED bulbs that can be dimmed. These will probably need a trailing edge dimmer rather than the leading edge dimmer that will be fitted if you’re replacing bulbs with a higher current flow. Most of the suppliers I looked at also sell the dimmer units.

Dimmable bulbs are more expensive.


When you look at bulbs, you’ll see a number of different designs, single LED, triple arrangements, surface mounted bulbs with 20~30 LEDs and bulbs that look like a bundle of LED PCB components mounted together on a bulb.

The triple and surface mounted models look neat enough for domestic purposes.  The single LED models look the most like halogen bulbs.    IMHO, the multi-LED bulbs would be more suited to workshops areas.

Coloured Bulbs

I didn’t consider using these, but there are a number of bulbs that are coloured or even can change colour by using a remote.

And So

I started looking a year ago, and the price has dropped continually over this time.  Unless you’re replacing 12v systems, and so need to replace transformers or you’re using dimmable lights, replacement is easy, so if you don’t want to replace everything at once, you can do it piece by piece (targeting the high-usage areas first).

I’ve had one bulb that didn’t work out of the box & the supplier replaced this immediately.

Our electricity bill has gone down noticeably over the period, and whilst I wouldn’t say I’m looking forward to the power bills over the coming winter, I can console myself with the knowledge that things would be a whole lot more painful without this change!

I’ve just found someone else who has written of their experiences of updating to LED lights also. See his blog at



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