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Re: LED replacements for Halogen downlights - ISSUES

PostPosted: Sun May 01, 2011 11:34 am
by Sandivee
I'd be careful of those, we tested them out, and whilst they are quite bright, the colour is a bit off, beam angle is a little narrow, and the 4 I've tried are all dead after 300 hours testing at 8 hour intervals.

Once I pulled them out I found the plastic base was damaged by the heat of the lamp and has actually warped the pins and discoloured the plastic base AND the board which the chips are mounted to.

Impressed for $15, not impressed for the lack of lifespan. I guess that's why eBay is great!

Re: LED replacements for Halogen downlights - ISSUES

PostPosted: Sun May 01, 2011 7:01 pm
by zzsstt
And we're back to the same old story. Cheap LED's either don't last, don't produce much light, have dodgy colour or all three, whilst expensive LED's also often don't produce much light and need to last for many years to repay their capital cost and are therefore just as much of a gamble, as failure within a year or three creates an economic loss. $80 capital to save 10W (that's 0.23cents an hour, or about $20 for a full years use at 24/7) with far less light than a 20W Osram? Get real!

A while ago I would have said that I would be willing to trust an expensive Philips light over a cheap eBay unbranded one, but then I had a bunch of Philips CFL's that were complete rubbish, taking minutes to warm up enough to produce any significant light and then going dim and yellow very quickly (less than a year). So now I have little faith in any of these products, and tend to stick with "proper" fluoro's (linear or circular) that produce a reasonable light, have a reasonable life and a reasonable cost. Either those or the Osram "energy saving" MR16's that convert 20W into more light than any LED I've yet seen, and at less money, using a normal transformer rather than an "LED Driver" that varies in price (for the same thing) between $50 and $150 depending whether it's bought from eBay or an "eco lighting specialist".

Having said that I'm still looking at alternatives, but the results so far have not been great.

Re: LED replacements for Halogen downlights - ISSUES

PostPosted: Sun May 01, 2011 7:19 pm
by Gordon-Loomberah
Yep, LEDS aren't really up to the task cf. a 20W Decostar, I've done HDR photographic tests on them as headlights for my mountain bike headlights a few years ago, and the Decostar puts out more light than 12W (4X3W Crees)of LEDs and even a 10W HID, although the halogen's light is comparatively very yellow. The only advantage of the LEDS for the bike light is that a smaller battery is needed (less weight to cart up the climbs).
However, LEDs are improving, so I hope that before too long they will be comparable or even ahead, value and light output wise.

Re: LED replacements for Halogen downlights - ISSUES

PostPosted: Sun May 01, 2011 7:41 pm
by karlajensen
Gordon I did similar "tests" and found that when it comes to sources of intense light, like the HID
the location in the fixture was critical to having a "fair" comparison.

I'd put my 35W HID downlight against 150W of halogens and still kick their butt but I cant make them cheap enough to be viable -they need a massive kick to get going which no "cheap" power supply can deliver.

Re: LED replacements for Halogen downlights - ISSUES

PostPosted: Sun May 01, 2011 9:00 pm
by zzsstt
karlajensen wrote:I'd put my 35W HID downlight against 150W of halogens and still kick their butt but I cant make them cheap enough to be viable -they need a massive kick to get going which no "cheap" power supply can deliver.


$69 on eBay buys a 2 x 35W HID conversion kit for a car, comprising 2x35W bulbs and power supplies etc. Obviously that's a 12V DC system, but why should it be that much more for a 240V system? The specs suggest an 8amp startup current and a running current of 3.2amp, at between 9 and 16VDC. Using only those specs, and that exact system, if you added a pair of 100W 240VAC to 12VDC PSU's you'd have a 35W light that produced 80%(?) more light than a 50W halogen.

And it's half the price of the Philips MR16 LEDs that produces half as much light as the halogen!

I have HID spots on my ute, and apart from the slow initial warm-up (and the overly "white" colour, next time I'll get the 3000K version!) they are great. I also have a couple of 240V HID floodlights, which when warmed up are very impressive.

Sometimes I wonder if, once again, the lighting salesmen have pushed the cheap, easy, "trendy" and no doubt profitable LED's when other and possibly better solutions exist!

Re: LED replacements for Halogen downlights - ISSUES

PostPosted: Wed Jun 01, 2011 8:01 am
by Photon
I am in the process of designing dc lighting to run off a 22-30Vdc supply. With the halogen replacement type leds, do they have some sort of inbuilt current regulator? My plan is to either use these with halogen style mounting hardware with a dc-dc regulator to achieve ~12v or to simply pair lights in series.

The other way forward is to build a lighting system from discrete LEDs and run them off a current regulated power supply. More work but it might end up costing less (and looking uglier....)

ANy words of wisdom?

Re: LED replacements for Halogen downlights - ISSUES

PostPosted: Wed Jun 01, 2011 8:09 am
by Gordon-Loomberah
Not sure of the wisdom bit :lol: I almost went with DC / LED lights in my house, but when it came to the crunch, decided it wasn't worth the hassle/poor performance/cost and went with 240V, mostly CFL and T5 fluoros instead.

Re: LED replacements for Halogen downlights - ISSUES

PostPosted: Wed Jun 01, 2011 8:17 am
by Photon
CFLs is what we have right now and are fine. Its this big dc cable that i laid for the fridge, specifically its spare 10-15 amperes........ some of this will be for the internet modem and mac mini ps but there should be enough there for lighting too, about 8 amps at 25v. Enough for a LED lighting a small house???

Re: LED replacements for Halogen downlights - ISSUES

PostPosted: Wed Jun 01, 2011 9:56 am
by zzsstt
A 6W LED of the type supplied on eBay will provide task lighting only IMHO (and I've tried them!).

A typical 24VDC to 12VDC converter probably runs at about 80% efficiency (just a guess, but I'd be surprised if it was much better and not surprised if it was less!). If a room needs 10 6W LEDs to light it effectively, keeping in mind the beam angles and so forth that impact the number of lights required in addition to simple "amount of light", then that's 60W at 12V. Given 80% efficiency of the DC:DC converter, thats perhaps 75W at 24V, which is just over 3 amps.

If you assume 3 amps per room, then the "spare" 10 -15 amps will light between 3 and 5 rooms. However, the LEDs will cost a small fortune to purchase, as will the DC:DC converters. The theoretical high efficiency of LED's will be crippled by the inefficient DC:DC conversion process, and the higher the current the greater the loss in the cables. Remember also that you need to account for "worst case scenario" of all the lights being on at once.

Then, if you share most people's experience of the lower cost LEDs, they will start to fail within a year or so.

It is of course possible to do it, but there are easier and more cost effective ways to achieve the same thing. As Gordon suggested, T5 flouros are a good choice, though I personally haven't had much success with CFL's.

However it must be said that lighting is a very personal thing. The intensity and colour of light required s dependent on the person, and the function of the space. A flickering yellow candle is fine for a romantic evening, but will give you a headache (or a fire!) if you to to read the newspaper by it, and you'll risk losing fingers if you attempt to finely slice food. On the other hand the high intensity lighting levels required for fine work are not required in the lounge room when watching the TV!

I would suggest that you try and match the colour of all the general lights, it can be quite strange to move from a "warm white" area to a "cool white" one, and even more strange when looking from the outside at night and seeing different rooms (or even external lights) with utterly different colours!

Re: LED replacements for Halogen downlights - ISSUES

PostPosted: Wed Jun 01, 2011 10:17 am
by Photon
Thanks for your replies guys!

What I think I'll do is a trial room - the kitchen. This room is currently illuminated with a single cfl which is central to the workspace which is roughly square. That means of course that wherever I'm working I'm casting a shadow across what I'm working on (unless i sit on the floor against a cupboard!)

This is also where the 24vdc supply enters the house and the room where the lights are switched on for the longest period each day.