replacing halogen downlights with LEDs

Our house, like many others, is plagued by horrible 12V halogen downlights. We have about 30 of them scattered through the house. I’ve been experimenting with various ways of replacing them for a while now. Apart from the amount of power they draw, they are also a fire hazard. I’ve noticed far too many of the bulbs are close to pieces of wood, and I hate to think that would happen if a rat nested on a little used bulb that was then switched on.

First attempt – GU10 compact fluorescents

My first attempt at fixing this was a couple of years ago, when I replaced 3 of the 12V transformers with 240V GU10 fittings and put in some compact fluoro bulbs. I was never very happy with them, they are slow to come on, and don’t give as much light as I’d hoped. I’ve left those in, but decided on a different approach for the rest.

LED MR16 bulbs

More recently I’ve been trying various LED MR16 12V downlights bulbs, which can go into the existing fittings with the existing transformers. I’ve tried 3 different LED bulbs so far:

Subjectively, the best_led bulbs are the brightest, and they are the first ones we’ve bought that pass the WAF for my wife. The dealextreme bulbs are very cheap, but are also quite dull. They are fine for the less important parts of the house, but no good for the kitchen and marginal for the lounge room. The ledcentral ones are better, but not as good as the best_led ones.

The other lesson is that LED bulb marketing is crazy. They all claim to be equivalent to a 50W halogen, but none of them are. The wattage and lumen claims are also very suspect.

Measuring the power usage

I used a Arlec power meter and a multimeter to measure the actual power for these 3 bulbs and a “50W” halogen. The results are shown below (all the numbers are quite approximate, as the arlec meter only shows 2 digits for power).

Bulb AC power (W) AC current (A) power factor DC current (A) DC power (W)
“50W” halogen 58 0.24 96 3.65 44
“3x3W” bulb 12 0.12 40 0.34 4
“6W” bulb 13 0.12 43 0.37 4.5
“360 lumen” bulb 10 0.12 33 0.26 3

All of the LED bulbs consume much less power than their rating. With LED bulbs, we have the strange marketing situation that a ‘green’ device is being advertised as consuming much more power than it actually does. If that “3x3W” bulb actually used 9W, then it perhaps it would actually be a good 50W halogen replacement, but as it only actually uses 4W it doesn’t have much of a chance. LEDs are not that efficient.

I recently saw some 10W GU10 bulbs from ledcentral at Andrew Bartletts house, and they are really bright! They are the first LEDs I’ve seen which really could replace 50W halogens reasonably. Unfortunately they are currently $59 each, so I’ll be waiting for the price to drop before buying any of those.

I will also need to look at replacing my old transformers at some stage. With the LED bulbs I’m now using most of my power just heating the transformer. Some specialist LED transformers are probably worthwhile.

In the meantime, the best_led bulbs seem to be the best choice so far. We’re pretty happy with 6 of them in the kitchen.

2 Responses to “replacing halogen downlights with LEDs”

  1. In a related topic, this problem with compact fluro bulbs was raised in a discussion about photographic enlarger bulbs.

    For the entire existence of analogue photography using enlargers, it’s been incandescent bulbs. Power usage really isn’t an issue… The amount of time you have these on is minuscule.

    But getting replacements will be getting to be an issue… and the warm-up time of compact fluro doesn’t lend itself to repeatable results.

    So it may be that LED may save the day here too

  2. Joey Hess says:

    If the PV system you recently had installed is not just grid tied, but has a battery bank (typically 12v), you could skip the transformer innefficiency & tie your lighting directly into that

    Thanks for the tip about LED lights — I had not realized that they were a) so cheap now and b) 12 volt native. I am looking forward to replacing a lot of tube lights in my solar powered cabin now.

Leave a Reply