Regret do not fully understand the new (to me) GU10 LED lights. They are rated as direct replacements for 240V GU10 halogens. But LED lights are inherently 2V very low current devices. What happens to the other 238V?
Please does anyone have a pointer to an informed dscussion of GU10 style light fittings?
White LEDs and the underlying blue ones that drive them are typically about 4v and DC. Drivers from mains typically rectify to DC and then use a high frequency DC to DC converter to supply the right current for the LED rating at an appropriate voltage. It is critical that the current is right. LEDs do not react well to a fixed voltage drive.
Some LED lamps actually have several LEDs in series. A typical high power LED is now something like 7W or ~2A at 3.5-4v. It will draw approx
2/60A = 33mA from the mains (or 35mA allowing for inefficiency).
The DC to DC converters used are typically 90-95% efficient.
The main reason to worry is that to protect the building from the intense heat of halogen lamps the fixtures tend to be extremely well insulated. This can lead to overheating of solid state LED devices when put into a confined well insulated space the control electronics gets cooked (same also can happen to CFLs in glass sphere lampshades).
The LED doesn't generate much waste heat but it needs to be conducted or convected away to prevent excessive temperature rise. A CFL/LED will suffer shortened lifetime at >95C whereas a filament lamp will happily work with the glass envelope at 200C and a halogen is even hotter.
In general LED work better in fixtures where there is some airflow.
On Thursday 17 October 2013 10:12 jim wrote in uk.d-i-y:
There's a little tiny PSU circuit inside every one.
Yes - I am experimenting.
GU10's are not optimal due to the LEDs/PSU needing to keep cool to prolong life.
However due to it being a fairly common format I went with it anyway[1]. I have a number of open chrome fittings where the lamp is largely in free air
- the few flush ceiling fittings I designed to take very low power LEDs as background night lighting so only 2-3W per lamp - so I doubt those will have a problem either.
[1] I don't want a whole "lamp plus tranformer" - I want replacable lamps in fittings that allow me to chose better products when they come to market.
For open fittings - any lamp fits. Soem may look ugly though if too long and bulky. This may or may not be a problem for you.
For enclosed fittings like your typical flush ceiling jobbie, you need to do one of two things:
1) Buy LED compatible fittings - these are the same as normal GU10 housings, but quite a bit longer. The base is on free flex as usual so they will take more or less any GU10 lamp.
2) Buy LED lamps that state they are for normal fittings. Possible - restricts the choices and I suspect if you stick a 15-20W lamp in a normal flush fitting, the life will be reduced.
Personally I would stick to Philips, Toshiba or at a stretch, Megaman. Avoid BY& random brands and dodgey chinese unbranded or lesser know stuff - LEDs are notorious for lasting 5 minutes if poor quality.
I follow all your reply except where this 2/60A comes from...the "7W or 2A @ 4v" looks plausible, but the 2/60A has hit my blind spot. Please can you spell it out..sorry it is probably obvious but.....
The boiling point of water or more accurately the electrolyte inside the capacitors puts a hard limit on how warm they can get and survive. Once it starts to boil they go over pressure and lose it. Limit is 85C for cheap caps, 105C for decent and 130C for best (and a premium price).
The thermal cycling with expansion and contraction eventually allows diffusion to dry them out even if everything performs perfectly.
Even high grade electrolytic capacitors are only guaranteed for a worryingly short period ~4000hrs operated at high temperatures. I've had motherboard capacitors fail on me in well under 5 years from new. (and they are not run very hot but are under high ripple current stress)
It may be possible to use solid state electrolytes for capacitors in LED lamps eventually but so far they haven't managed it. LEDs are best used in fixtures with plenty of airflow and then they are fine.
Philips and Samsung are amongst the best I have tried so far (but not the GU10 fitting ones mine are B22 and E27). Some are even a realistic "warm white" and can be mixed with incandescents seamlessly.
So LED replacements for halogens should last a lot longer in a non-recessed light fitting, especially if the lamps are spaced away from the celing a bit?
Also, LEDs themselves don't like high temperatures. Efficiency and life expectancy drop off much more rapidly than other semiconductor devices. The most difficult part of most LED lamp designs, and the limiting factor, is cooling of the LED chip itself. This is even more challenging when trying to design an LED lamp in the size/shape of something like a GU10, which was never designed with LEDs in mind in the first place.
They won't work. They all have a minimum, 20-60W is a typical rating. You can buy new low powered 12V supplies for LEDs, or you could use just one to feed many more lamps, but there seems to be a better choice of retrofit LED lamps in GU10 format.
These are for driving dedicated LED luminares where the connections go directly to the LED chip, not MR16's.
You are not making much sense here. I'm sure the rest of this thread gets very scientific about watts, amps and volts, but the main thing is, the voltage may well be low per individual led elements, but if you use a lot of them to create the light output then you draw a lot of current at the low voltage. Obviously its more efficient than the original, but as long as the circuit that runs the leds is quite efficient, then there is no problem at all. The side issues are often funny interference on radios and possibly not very good use with a dimmer.
That is the simple Simon version Dumbed down by the guide to BBC idiot proof science. grin.
It can be and of course it also can be designed so it does not dissipate such a lot of heat. Many of these things tend to saturate the cores of the inductors which can cause heating.
Although there are some LED based lamps that run a chain of LEDs and work at a higher voltage than 4v there are now single dies that can handle 7W and 10W directly. Series or parallel networks also occur.
Cheap ones tend to use many smaller LED dies in a corn bulb configuration to try and mimic small halogen bulbs on 12v. eg.
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Their big advantages are no UV and very little radiated heat.
One other point is that the emitting area on the latest generation of LEDs is close to the surface brightness of the solar photosphere - it is not a good idea to stare directly at it close up.
Series allows higher voltage and slightly better efficiency at the cost of losing a whole chain if a single one fails. Parallel increases the current draw which isn't ideal in a small space with thin wires.
You have to be very careful about whether or not the CFL or LED lamps are dimable and check the rules on the side of the packaging carefully. A non dimmable one can catch fire or cause the dimmer to overheat under some circumstances. Basically the two controllers fight each other - one is trying to limit the power and the other to keep it constant!
You can also have trouble if the low power of the lamps takes the dimmer below the minimum power where it is guaranteed to work correctly even with *dimmable* low energy bulbs. You may need one genuine filament bulb to keep the total load above about (eg 40-60W). RTFM
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