I'm using 230V GU10 LEDs but I think on a new install I'd go for 12V LED that use 20-24 of the 5050 form factor die and deliver >350Lm

Installing 12V lighting is notifiable under the Building Regs unless the electrician does it. You should design the wiring to cope with the much higher current of 12V halogen just incase you sell the house and the new buyer fits these bulbs. Otherwise there is a real fire risk that could come back to you...The high current draw by 12V halogen is the reason installing 12V is notifiable where as 230V it isn't allways.

Oh yeah, if you're going for LEDs, not halogens, then a low-voltage constant-current driver might be the best idea, but I'm not up to date on LED fittings etc.

TimSmall: I just read something within the last couple of hours that for MR16-style halogens the lower voltage versions had the higher luminous efficacy due to the more compact filament.

Rgds

Damon

The best bet if using conventional halogen fittings, the most efficient option is probably to use a dimable constant-current driver (instead of the conventional 12v halogen "transformer") like this:

http://www.aurora.eu.com/ProductPages/PowerProductDetails.aspx?g=248&c=&b=5&oc=556

(available for £30 or so).

and use it to power a couple of strings of "uncontrolled" LED bulbs, if you can find them (probably not on reflection, the average bod would just plug them into a halogen transformer and blow them up).

Hmm, bloody halogen downlighters... Hopefully the LED market will get a bit more sensible in the next few years, but then I was saying that a few years ago.

I' m regretting downlighters, they let loads of drafts through the holes in the ceiling. Next time would choose dangling light fittings.

White LED forward voltage drop more like 3.3V if that's what you mean?

Rgds

Damon

Posted By: TimberSo, going back to my previous post, if most white LED chips take 3.3v, would a regulated high current 3.3v rig be a reasonable idea.

No, not really. The problem is that they need to be fed a specific current rather than a specific voltage. The actual current through them is very sensitive to the exact voltage and the voltage corresponding to the right current varies slightly between devices, with age and with temperature. E.g., you might have two LEDs next to each other, one needing 3.29 V and the other 3.31 V. If you feed 3.3 V the one needing 3.31 will be very dim, not just by an amount proportional to the reduced voltage as the current will be also be greatly reduced, whereas the one wanting 3.29 V will take too much current and will likely burn out quickly.

LED installations always have some sort of circuitry to control the current. Sometimes it's an active semiconductor circuit to form a constant current source. Other times it's just a resistor in series.

Often that circuit can be shared between multiple LEDs in a series chain hence it's often a good idea to use a voltage a little in excess of some number of times the forward voltage drop of a single LED with that many LEDs in each series chain.

My first time, and not seen them fitted yet but we're using http://www.aurora.eu.com/ProductPages/LampProductDetails.aspx?g=7822&c=&b=136&oc=84 LED swivelable downlighters (also avail fixed) £36 + £9 driver. Why do anything else now these have come of age?

Posted By: fostertomMy first time, and not seen them fitted yet but we're usinghttp://www.aurora.eu.com/ProductPages/LampProductDetails.aspx?g=7822&c=&b=136&oc=84" rel="nofollow" >http://www.aurora.eu.com/ProductPages/LampProductDetails.aspx?g=7822&c=&b=136&oc=84LED swivelable downlighters (also avail fixed) £36 + £9 driver. Why do anything else now these have come of age?

exactly what i was waiting for, exactly 9 months too late!

maybe once my MR16 12v LEDs start to blow I could consider replacing them with constant current devices, one string at a time...

Incandescent ~ 13lm/W
Latest commercial LEDs ~ 100lm/W

Looks like 230V 5W 400L GU10 are now down to around £3.50-£4 compared to £7-£11 this time last year..

http://www.ebay.co.uk/itm/Best-price-for-20pcs-GU10-4-5-5W-24-5050-SMD-LED-light-450Lm-180-Warm-White-UK-/180852631499?pt=UK_Light_Bulbs&hash=item2a1ba827cb

Great - thanks

...soooo....

for the cost conscious green builder I need to look for 12v, MR16 "5050" 450lm bulbs:

http://www.ebay.co.uk/itm/MR16-4-5-5W-24-5050-SMD-LED-light-450Lm-180-Warm-White-UK-/180852735585?pt=UK_Home_Garden_Night_Lights_Fairy_Lights&hash=item2a1ba9be61

in basic fittings with lots of space around:

http://www.screwfix.com/p/robus-adjustable-round-low-voltage-downlight-brushed-chrome-12v/71123

plus something like one of these for each 10 or so lamps:

http://www.screwfix.com/p/240v-to-12v-350ma-9w-led-const-current-controller/66599?cm_mmc=AffiliateWindow-_-DeepLink-_-Na-_-Na&source=aw

Now the plan was that my electrician would do the 240v wiring up to a 'transformer' position and I would wire in a 12v 'kit' with LED bulbs as part of the 2nd fix which I am doing, with him to check and test. Now we are talking constant current and lighting positions in series with cabling to suit drop, load, distance etc, I think that he may have to be involved in sort of 2nd 1st fix.

J

100lm/w is still relatively state of the art (130 available from Philips and Cree these days but not in WW)
You don't get it at those prices.
The lumen figures claimed by many cheap LED lamps are clearly rubbish.
If those ebay 5050 lamps are 100lm/W I will eat my box of cheap lamps that just didn't measure up.
I know they are pricey but the Aurora LEDs that FosterTom pointed to are _much_ brighter and nicer light quality than the 5050SMD bulbs IMHO. They also are ventilated/heatsinked and run fairly cool - they have been proerly designed.

I would be quite wary of anything where switchgear and LEDs are crammed into a normal halogen glass capsule just because that is what the factory happened to have lots of. It's just not a sensible LED design.

Take those ebay lamps for example
20 lamps for 72 quid is £3.60 per lamp.
At 24 per lamp that's < 15p per LED. And that's ignoring cost of glass capsule and PSU electronics. Something tells me those are not the 100lm/w LEDs that cost several quids each.
They are probably something like this:-
http://uk.rs-online.com/web/p/visible-led/6935167

Even so, 15p is still crazy cheap. It's likely these are the LEDs that failed to make spec when sorted. The ones that make >= 19.5 lm/w make spec and can be sold as such at a decent price. They don't throw the rest away though.

But lets give benefit of the doubt. Lets say these are real full spec LEDs.
The datasheet says typical is 24lm from 150ma at 3.5V.
That would be over 500lm but only at 3.5 x 0.15 x 24 = 13 Watts.
At 4.5W and 100% efficient PSU we only have 50ma per LED.
Datasheet says that at 50ma this LED outputs 10 lm.
So, even if they are full spec LEDS and 100% PSU we still cannot possibly get more than 240 lm.
That is way short of the claimed 450 lm (which is very suspicously the magic 100 lm/W).
And that 240 lm is also spread over 180 degrees because the SMD LEDs have no lens.

Compare that with a 50W halogen that typically outputs 900lm. And most of that projected forwards thanks to a reflector. The cheap LED doesn't come close in luminous flux.

It is a lot to ask of an LED but the relatively expensive 7W Aurora and Philips LED lamps with heatsinks, ventilation and lenses enclosing the LED do come fairly close to 50W halogen in performance and light quality. You get what you pay for. The ebay SMD specials surely are a bargain for the price but I would not want people to get the idea that this is what state of the art LED lighting looks like.