12V MR16 halogen bulb replacement with LED's

[Rob G]

I've been looking at replacing the halogen 20 W, 12v MR16 bulbs in a 4 bulb ceiling spotlight unit - the sort with two 600mm wires/rods from a central boss.

The number one query is that this a wound transformer (12v 100W) driven light - I picked up a comment that this might be unsuitable for LED bulbs ( lack of regulation ?). Correct ?

Secondly I see 4 types of light source - multiple smd LED's, multiple 'ordinary' LED's, 3 off 1W LED's and 1 off 3W LED. Now, forgetting for the moment about the possible transformer problem, am I right in thinking that the multiple LED bulbs produce a flatter light output, and the latter two types are more like spotlights.?

Thanks Rob

[Andrew Gabriel]

It will probably work fine - LEDs won't much care if voltage is a little higher.

There's no golden rule - it will depend on the optics of the units. IME, the multiple 'ordinary' LED's tend to produce a very narrow beam which seems intense when you look back up it at the lamp, but the total light output (lumens) is actually extremely low - about same lumens/watt as the 20 W MR16 you are replacing, but given it's probably less than

1.5W, it will have less than 10th of the light output. Actually (to a slightly lesser degree) that applies to all of them - no one makes an MR16 LED with same output as a 20W lamp, because it would get just as hot, and kill the LEDs. 4W is currently about as good as it gets. A 4W 100lumens/W LED would be same light output as 20W MR16, but you would probably have to pay the best part of £100 to get an LED that efficient.

[Mike Barnes]

Andrew Gabriel :

It sounds as if LED replacements for incandescent MR16s need a lot more development before they become worth buying. Yet there seem to be a lot on sale.

[Dave Plowman (News)]

Don't these LEDs have a driver built in? If so, it should be very tolerant of voltage.

I bought a few drivers off Ebay that looked like they were made for MR16 by the pins and am using them in the car. On the bench, they seemed to tolerate 9-15v DC with no change in output.

[Andy Dingley]

Not IMHE. It's the only sort they'll work with. The LED modules themselves generally have an on-board regulator.

If you connect a 12V LED to an electronic lighting PSU, they detect too little current drawn, interpret this as an open circuit and then switch off.

[Andrew Gabriel]

Retrofitting LEDs in place of most incandescent lamps isn't going to work. If they become established, it will be in completely different lighting forms, such as illuminated coving. Their efficiency is quoted at 25C junction temperature and drops rapidly as you get to 80-100C where they tend to operate in retrofit lamps.

LEDs do actually make good spotlights too, but spotlights make very poor general lighting, as demonstrated by most MR16 installations.