Darren_Dons
Member
Hi all,
I've been looking at installing some LED downlights in my place (replacing halogens) and am impressed with almost everything I hear and see, however I have heard that they can fade quite rapidly. I was told by one person that they begin to fade considerably after only months of use and then it's downhill towards dullness from there.
Does anyone have any info on this/can prove it wrong and convince me to buy?
Cheers.
I think it depends on the fitting. Some fittings that don't have enough heat sink on them will deteriorate quickly as the heat kills the led. Others that keep the led cooler should last longer though there are other factors also. The bigger brands like brightgreen or pierlite or osram should give reasonable staying power. Lucky dragon fittings from eBay are probably more susceptible to the fading problem though some are probably fine too.
Lance
Key Master
There's two things that make LEDs fade. The first is the use of low grade phosphors. White LEDs are just blue or UV LEDs with a phosphor over them, the phosphor works the same as it does in a fluoro tube, emitting white light when excited by the blue or UV.
The other problem is heat. Many downlights run way too hot, either from poor bulb design or from fittings that provide inadequate ventilation. This causes the phosphor to degrade faster. With LEDs, the cooler they run, the better.
However, the problem of heat degradation is much worse in many low cost LEDs and hence LED bulbs than it is in higher grade brand name LEDs like Cree, Osram etc. Indeed, some manufacturers, Cree being one of them, are rating their lighting grade LEDs at 85 degrees instead of the more common 25 degrees, and lifespan is often rated at 50 or 70 thousand hours at those temps.
So, if you want LED bulbs to last, buy ones with Cree or similar higher grade LEDs, or make sure you bulbs are running as cool as possible.
Unfortunately, LEDs, being more complex than other forms of lighting, are out of the knowledge range of most people and so you will hear a lot of "LEDs fade too quickly" or "LEDs don't last" or other similar incorrect statements where people will tar all devices with the same brush simply because they bought the wrong devices for their situation because they don't understand the technology...
canyoner
Member
Further to what Lance has said.
Many of the decent LED manufacturers qualify the life of the LED as so many hours (usually 30000-50000 hrs) to a percentage of their original output.
i.e. they warrant their LEDs to be at 70% of their original output at 40000 hrs of use.
Its not just LED lamps which have this degrading output over time. All types of lamps (fluoro, metal halide, halogen, etc) all do it.
Guys, I'm a little behind on the whole LED Lighting thing. Is it hard to go back once you have installed LED fittings?
I am currently building a house and trying to decide whether the future is LED for downlights - any opinions - I hop I'm not hijacking this thread... 
Darren_Dons
Member
SO heat is the main issue. It seems then that you get what you pay for and the bigger, more expensive brands are worth it.
WIth heat being the key, In my comparisons I saw that brightgreens have thermal monitoring on board that can dim the lights to cool them down if too hot to preserve lifetime and brightness. I couldn't see this offered by pierlite or the others. I have also read in other forums to steer clear of any that have a fan inside.
renewable said:
Guys, I'm a little behind on the whole LED Lighting thing. Is it hard to go back once you have installed LED fittings?I am currently building a house and trying to decide whether the future is LED for downlights - any opinions - I hop I'm not hijacking this thread...
From what I understand it would just depend on the cutout size in the ceiling, unless you go the retrofit option and stick them in place of halogens.
Im pretty set now on LEDs after reading this, quality pays off it seems. If they last as long they say I wont need to go back.
marie
Member
Well I have a whole renovation happening and I have today just ruled the downlights out. My electrician is not going to like me, because tomorrow I will fill all the huge gaps he wants and needs in my ceiling. By the way the guy does not care about insulation in general and I have refitted batts he had dropped on the floor because he did not like them in his way. But today I had the Ecomaster people advise me on the appalling job my insulaters had done. (I can only HIGHLY recommend Ecomaster as they have come to the rescue of my federation home, with tested, thorough and thoughtful advice throughout the years that we have been trying to improve our thermal comfort). Anyway today they were looking at those gaps with me, and pointing out that such gaps will destroy why I am trying to achieve in terms of insulating our house, when they dropped the surface mounted lighting bomb! Almost an heresy in our time of discreet recessed downlights!!! But this is it I am going to find nice light fittings that can be ceiling mounted and work with my fancy pendants. Any advice on ceiling mounted lights fittings is welcome! Sorry if I am highjacking that link!
Eugene
Member
Here is some info about the cause flickering light. It is not specific for LEDs, but only halogen bulbs, but the problem is still the same. Heat.
As Darren_Dons said, you get what you pay for.
Morbo
Member
got some 1 and 2 W LED lamps off ebay just to see what happens. Put it into hallway and bedrooms thus reducing the input from 500 to 10 Watts. They were amazingly bright for what they were. Did not take long for single LEDs to fail.
Now, donlights for a start don't utilise much of the light, just because they are recessed. Some goes nicely into your roof. And so does some of your heat just because you cut nice holes into the paper thin ceiling. (plasterboard is the worst material on the planet imo). Plus they attract insects that somehow crawl in and eventually the fitting is full of little bugs.
You would need at least 5W LED for 9W CFL. You can light a room on 20 W in a fitting, 40W CFL or 20W LED downlight. Plus the CFLs have softstart, so the wife switches all of them on just to see something, 5 min later when they are "on" you find yourself switching half of them off. So some rooms just got those round ones surface mount fittings, switch on, they are on.
The only reason for downlights is its hard to find some ok looking fittins. Half are Victorian style which is not really appropriate in a 50s timber shack or 2010s fibro townhouse?
tom
Member
Hi Marie,
I'm with you. Our new house will have no downlights. We were told to use BrightGreen LEDs by the Architect, but even though BrightGreen say you only need 20mm clearance around them, the same Architect says that Australian standard specify 200mm clearance. And regardless of what clearance you have, you can't cover them with insulation, even with a downlight cover. So we would have had 39 half metre holes in the roof with no insulation. I really can't understand why anyone on this site would even consider downlights, LED or otherwise. Go to all the trouble of insulating your walls, double glazing your windows, panels on your roof, efficient heating, orientation ... and then have all these holes in the insulation in your roof? Besides downlights are generally ugly, they only seem to be popular because no thought is required to choose them, and also because people have lower ceiling than they used to.
Morbo
Member
tom said:
Besides downlights are generally ugly, they only seem to be popular because no thought is required to choose them, and also because people have lower ceiling than they used to.
Suppose its 2.4m now, not too bad, little less trouble to heat. Up there may be 26 deg down here 22. Anyway, there is some round flouro lights that don't look too shabby and they are on 100% within a few seconds.
lecky22
Member
tom said:
the same Architect says that Australian standard specify 200mm clearance. And regardless of what clearance you have, you can't cover them with insulation, even with a downlight cover. So we would have had 39 half metre holes in the roof with no insulation.
The Aus standard of 200mm clearance applies to lights that operate at a high temperature, 100 deg or so and therefore get very hot. Brightgreen's (and other leds) do not get anywhere near as hot and therefore do not need the clearance and aren't covered by that regulation. They need much less clearance because of their low heat, they are fireproof.
This means you won't have large uninsulated areas in your roof, adding to the energy efficiency of the Brightgreens.
alfresco24
Member
Elvis... read thru http://apps1.eere.energy.gov/buildings/publications/pdfs/ssl/perkins_fairfax09.pdf for insight.
It's a little old but still reasonable. Costs have come down and yield/performance has gone up - maybe 30%-50% overall improvement since these 2009 numbers.
Use 150mm diameter wafer with 3mm sq die to calculate the total number and individual cost and extrapolate that using the distribution of cost shown in the pie chart to come up with a final cost. (A 3mm die will yield a 1W-5W LED depending on chemistry and die packaging)
It's all just math
wlb
Member
In addition to Cree, the other highly reputable LED chip manufacturer is Nichia.
The other thing that kills LEDs is high voltage. This is mainly a problem with off-grid systems running LEDs at battery voltage, when the batteries are being charged. Then the quality and specs of the power supply that is built into the LED lamp is very important.
They have certainly come a long way from when I first used red LEDs as engine warning lights on the dash of my FJ in 1969. I now have a small LED Lenser torch and a large LED Maglite torch which produce amazing focused light. The Maglite could almost knock a possum out of a tree at 400m with just three D-cells.
tom
Member
Even with a sealed box, you still can't put insulation over the top of the downlight. Even LEDs need to cool, and they need airflow to cool. (In fact any heat sink operates under the assumption of airflow, just open your PC up and look at the big fan on your CPU heat sink). Seal the LEDs up and stop the airflow, and they will run hotter and last a lot less.
