Led GU10

[LightPlanet]

Hi Ken,

I think that everyone is struggling slightly because it is a complex question without a clear answer. I'll have a crack at it though!

LED - best production products, light output at source, initial illuminance 110 lumens / Watt. Some of the chip manufacturers have achieved greater than this in the lab - see the Cree web site for details of some of the most impressive figures. Thermal management and drive current are the key factors relating to maintained illuminance - but our best products sustain 90% of initial illuminance after 30,000 hours. There are lamp losses associated with LED which mean that efficiency with current products is around 75 lumens/watt. Further losses in drivers etc bring this down to 65 lumens/watt. This is for current, affordable systems. We have a version of our GU10, for example, which has an output of 720 lumens / 7 watts, but it is expensive and there is a compromise in lifespan.

CFL - initial illuminance in best production products is around 85 lumens/watt. This is non-directional, so in many cases there are considerable lamp losses. There are also ballast losses, which mean that, on average, across bulb formats, CFL and LED are fairly well matched for overall efficiency. However, CFL bulbs take some time to warm up and achieve maximum output. During this phase they are very inefficient. The efficiency also drops off rapidly over time, which means that, over the life of the bulb, the overall efficiency is considerably less than LED.

Halogen - again, there is considerable variation in efficiency, depending on the quality of the product. 15 lumens per watt appears to be the average efficiency of a typical GU10 - so a 50 watt bulb would have an output of 750 lumens. As with the other bulb systems, there are lamp losses. A GU10 uses reflection to direct the light - and this is very inefficient. Measured output varies considerably depending on quality of the reflective surfaces, filament and gas content of the bulb.

Next issue - measurement. This is a tricky one and I don't claim to fully understand it, but - light measurement devices have been designed to measure full spectrum light. This includes parts of the spectrum around UV and IR which are not relevant to human vision. LEDs only produce very narrow wavelengths, so all of the light is applicable to human vision. So, according to this assertion, measured light from an LED is more "valuable" than measured light from an incandescent light source. I recently read a very complex report on this - or at least I tried to!

Last thing - LEDs are more efficient in higher colour temperatures. Compare the efficiency of the warm white with the cool white in the chart above.

Hope this helps......

Simon

[wookey]

Excellent - someone selling LEDs who knows what they are talking about (I see nothing to disagree with in your summary). Commendable :-) And thanks for making the effort to post here.

So now I have a question for you: where is a good-value source of LED driver supplies? I have found very cheap, embarassingly inefficient drivers (GBP 8, 60%) and very expensive, very efficient drivers (GBP 90, 93%). I feel there really ought to be something in between, but almost no suppliers give efficiency numbers for their drivers/supplies.
My examples above are for 240V-> 12V voltage-regulated, 15W nominal supplies.

I currently have several 6W 65Lm/W LED strips which can be driven by either 12V voltage-regulated or 0-2A current-regulated supplies. If only I could find some supplies for them that are at least 85% efficient without paying a fortune, I'd buy a pile more and do the whole house (strips now available up to 80Lm/W - not seen 100 yet).

This question also brings up an interesting question about how power architecture for LED lights should work. LEDs are current-controlled devices so we really ought to be getting free diming with current-controlled supplies, but in practice veryone seems to be selling LEDs by supply voltage (e.g '12V', '24V', and either putting regulators in the bulb/strip (making them non-dimmable) or assuming a well-enough regulated voltage-controlled supply.

A whole-house supply might be more efficient than lots of tiddly ones (one well-engineered 12 or 24V supply rather than 15 crapy ones), but then you can't do current-control (dimming) in the supply (because the whole house would be affected) - you'd have to waste power in a dimmer. So maybe this architecture only makes sense if you don't want dimming (and I don't particularly, but I know others do and it's so easy with LEDs it seems a pity to not enable it). So if we go back to individual lamp current drivers then a) where do we get good ones, and b) how is the dimming control done? Simple POTs in the light switches, or something much fancier? Perhaps the driver should go in the light switch pattress? And finally is there any mileage in a hybrid setup with say a 48V low-voltage 'main' with a lot of smaller drivers, one for each LED unit? This keeps the high currents reasonably localised and the end-drivers to safe low voltages.

I'm really not sure where the efficiency, value and versatility optimums are. It's going to take a while for people to understand the potential of infinite forms of LED lighting.

[Kombi]

I have taken the plunge recently and bought a load of 5w LED bulbs to replace my 17x 50w halogen as I couldn't bear the reading from my Current Cost display and it would have meant a bigger Multiplus to cope with the demand.
I tried many different models but I ended up choosing the Decor Triple LED (although it has 4 actually) in warm white, a good replacement for my 50w halogen. True the "cool white" version was a little bit brighter but too cold a light for my liking. I tried some CFL but was very disappointed with these, same with some 7w LED which were not any brighter than the 5w. The only down side is that they remain very expensive.

[wyleu]

Wookey raises a very good point. It's very easy to focus (ahem) on the lamp end of this but it really needs to be regarded as an overall system? I like the extra efficiency of combining the control elements locally, with local motion detection. with power provided at 40~ Volts with a control line of some sort interconnecting lighting fittings. Install it first as Emergency supplementary and then transit away from the 240 Volt infrastructure.

If we're providing local control, can we add an efficient rectifier and smoothing mechanism?  because there might be advantages in distributing power as low voltage AC rather DC. It doesn't match quite as well to Batteries/ PV etc but it doesn't need to be synchronous with house mains so the head end electronics don't need to be clever, only efficient? Bit off topic but just some thoughts.