Seasons greetings one and all,

I have a low wattage MR16 dimmable halogen cable light with four bulbs that I would like to 'upgrade' to LED. When I last checked, it seems that it is necessary to exchange the transformer.

But all the numbers are confusing me and not sure what I should be looking for. Is it possible to just do a straight exchange, the same way if exchanged the 240v halogen downlights for LED bulb replacements? Or is it more complex then this?

Thanks

You need to be drawing 80 watts as a minimum. So even if you can find 20w mr16’s there’s no point in not using 20w. Halogens as they’ll both be using the same amount of power. I had the same problem in my rentals, to satisfy the epc assessor i ended up changing the whole fitting , by far the easiest route.

So I need 20W LED to get to the minimum transformer requirement?

Or just exchange the transformer for an LED 'driver' that will run 4 x 5w bulbs. Only problem with an exchange, will it fit within the current housing?

Posted By: RexSo I need 20W LED to get to the minimum transformer requirement?

No - You need 4 x 20w LEDs

Posted By: RexBut I assume that 4 x 20W LED will not save on my electricity costs when I current have 4 x 20W halogen?

Correct, no saving on electricity - but you will get much more light (about 200 Watts worth of halogen light if you believe the advert)

It is best to change the measurement used for light output. Watts was never a measurement of light, it is a measure of power used. Using it for light worked when all you had was incandescent bulbs and light output was in proportion to the Watts. Now there are several bulb technologies (LEDs, CFL, halogen and some legacy incandescent) you need a measure of light rather than power used.

The unit used is Lumen (shortened to lm) and you will see this on the bulb box along with the power used (W) the colour rendition of the bulb typically 2700k to 4000k) and the EU energy standard (A-G)

So you (and old farts like me) will have to stop thinking how many Watts I need to light a room but how many lumens I need.
Watts are just how much power you need to get the lumens you need and this varies with the bulb technology.

Just remove the transformer and fit 240V fittings/bulbs.

Refused to use any transformers in my second build.

Thanks; how come it is all so confusing, or am I just somewhat dense?

Given that the fitting is one of those twin wire lights and the individual lamps have a metal fitting that punches through the insulation, fitting 240v bulbs is probably not the best idea.

So 4 x 5w LED MR16 bulbs and an LED driver (transformer) of around 30W should be OK? My slight concern is that I don't know the lumen value of the current 20W halogen, but if 5W LED is the equivalent of 50W halogen, everything will be much too bright.

So yes a similar light level can be achieved.

Look at the lumen level produced by each respective bulb and ignore any marketing speak about being equivalent to any amount of Watts.

I had a look at a couple of halogen 20W bulbs and the lumens produced were 235 lm and 350 lm so say about 300 lm for a 20W halogen bulb, the LEDs you quote above are 210 lm and 345 lm with the 345 lm LEDs being dimmable. I would go for the 345 lm bulbs regardless of whether you use a dimmer or not. Generally bulb light output diminishes as they age so going for 210 lm might be a bit dim after some time.

As for the transformer - It is recommended that the transformer used is only run at 80% of its rated max. capacity. Less than 80% is OK but too much less if dimmer circuitry is involved may mean the dimmer won't work properly. So choose your bulbs and then choose a transformer to match the bulbs. If you go with the 4 x 3.4 W LEDs then I would get a 20W transformer but the 30W would also work but make sure that the Wattage of the bulbs is within the spec. of any dimmer circuitry.

BTW the halogen bulbs are producing about 15 lm / Watt whilst the LEDs are producing about 100 lm / Watt. About 6.6 times as much light / Watt which is why LEDs are so much better.