LED manufacturers

[Graham Harrison]

Looking for GU10 LEDs I find several problems

1) I've never heard of many of the manufacturers so how do I choose? Price is not necessarily a good indication of life. 2) The bulb needs to go into a fitment which has a maximum 35w warning. I seem to be finding 5w LEDs which are the eqivalent of 50w according to the blurb on sites. As I understand it the 35w is based on heat generated as much as anything else so are 5w/50w the appropriate replacement given that (I believe) LEDs run colder? 3) Is there a definition of "cool white", "warm white" and other such terms or is there another term I should be looking for to determine the nature/amount of light I'll be getting?

Thank you.

[Tim Streater]

I went with whose offerings seem to be quite satisfactory.

Well, figure it out. A 5W LED produces most of the 5W as light. A 35W light produces most of the 35W as heat.

There won't be a precise definition because I expect it varies between manufacturers, but cool white means a bluer white and warm white a redder one. It's usually quoted as a colour temperature but I don't know whether that implies a specific colour profile (to match what a hot body like the Sun provides, f'rinstance).

[Harry Bloomfield]

Graham Harrison presented the following explanation :

The 35w is the maximum heat rating for the fitting and its shade. Where LED's are concerned, there is much less waste heat so for the fitting at least it would not be unhappy with a 35w rated LED, near equivalent to 300w in a normal bulb.

The problem with LED's and their rating in a fitting, is that heat buildup in the LED can damage the LED module itself. These LED's are much less tolerant of heat than normal incandescent lamps.

[alan_m]

Its usually the power supply in the base of the bulb that fails rather than the LED itself.

Unfortunately a lot of GU10 down light fitments are not particularly suited for LED bulbs because the lack of free air ventilation. The electronics get too hot and fail prematurely

You are correct - the 35W rating is based on the heat generated by a typical traditional GU10 bulb. A LED with the equivalent light output of a 35W traditional bulb will run a lot cooler. However a LED can still get too hot if fitted in something without sufficient ventilation

Cool White gives light towards the blue end of the spectrum. With better bulbs this equates more to a light output similar to daylight. Warm white gives light towards the red (orange) end of the spectrum more akin to what people expect from a traditional filament light bulb.

Which you choose is down to personal preference. Some people will trash cool white/daylight with a vengeance and warn of dire health consequences if used but if needed for working, reading or failing eyesight the better contrast these coll white bulbs seem to give may be the better option. Most of the LEDs in my home are cool white.

[John Rumm]

The commonly accepted figures seem to be around 2700K for "warm white" although some will go up to 3000K or so. Cool white is often around

4000K, and Daylight normally 6000K+

The cooler you go (where "cooler" in reality means higher colour temperatures), the more brightness you will need to make the light see properly colour balanced for the eye. Too little brightness for the clout temperature will tend to result in the light being perceived as "blue".

[Muddymike]

I'm looking into buying 15 MR16s for our new kitchen. Has anyone experience of the brands CPC sell? @ £1.85 each ther seem to be good value.

Mike

[Theo]

I've bought a load of LED lamps (but not MR16s) from CPC/Farnell - they seem fine, but I haven't run them for long enough to check longevity.

Theo

[Dave Plowman (News)]

My experience of buying such things is to go to a supplier who knows he'll have problems by supplying duff gear. Which rules out perhaps many retailers. Customers buying one of anything relatively cheap there - and it fails - are likely just to shrug their shoulders.

That certainly was my experience with tungsten GU10. Bought from a shed or supermarket got ones which failed in short order.

Got replacements from TLC. They had the expected life. Since they generally sell to the trade who don't just by one or two, returns for faults would be far more of a problem to them.

[The Natural Philosopher]

No. the 5W LED still produces most of its output as heat.

I think its like 300mW of light in each case....

[whisky-dave]

Light isn't measured in mW.

It gets confusing due to two types of efficiency there's also the efficiency of the amount of visable light compared to non visable (human eye).

[PeterC]

Then there's the power factor - around 0.5 - but in the worst case it'd need rather a lot of them to get anywhere near the rated power for the fitting.

[Fredxx]

It can be very easily. Just count photons and their energy and you have power.

That's sensitivity, and it you have 'white' light then the visible range will already be determined.

This also mentions 'output power' and a max of 250 lumens/watt, on a

100% conversion of energy to light.

[Fredxx]

suggests a lumen represents at least 1/683W assuming green light, the eye's most sensitive wavelength.

Suggests white light is a max 251lm/W If further truncated to remove wavelengths the eye is least sensitive to you can get up to 348lm/W

The article is confusing since some tables include 'Overall luminous efficiency' which by definition by green being 100%, white light is always going to be less than 50%.

Nevertheless the wiki article does suggest a "21.5 W LED retrofit for T8 fluorescent tube (230 V)" is going to have a efficiency of 50% wrt to theoretical limit for white light. That is pretty good.

[ARW]

Before you buy them you need to look at how the existing lights are powered.

It might not be a straight swap depending on the transformers that you already have.

[JoeJoe]

No idea, but I bought the cheapest GU10s that I could find at the time - off eBay, non brand ones. Warm white, just before Christmas 3 or 4 years ago, all used in the kitchen - around 15 in total.

Plenty of use - and plenty of on-off's. All are still going strong (I bought a couple of spare ones at the time. Just checked - they are still in the garage...).

Mine are 100% cold at all times. I bought 8W instead of 5W. I bought a couple of 5W to try first, but went for 8w instead since there is hardly an increase in terms of electricity usage, but a much better light output.

"Cold white" is very unpleasant in my opinion for domestic use. I think they also refer to it as Daylight.

These are the ones that I bought (well, by eBay item number):

The ones they now offer are definitely different from the one that I have - there were no dimmables and/or 9W ones available at the time.

[whisky-dave]

But isn't even if you claim it's easy to count photons. Perhaps this isn't why the SI unti of light isn;t the watt.

no it isn't.

wrong.

but only for that product.

[Fredxx]

Yes it is, I suggest you have a look at

No I'm not. For low light levels, the response of the human eye changes. However where colour is perceived the CIE standard curve is used to convert radiant energy into luminous (i.e., visible) energy.

This might assist:

No, it's the maximum for any product that produces a nominal white light:

Suggests white light is a max 251lm/W If further truncated to remove wavelengths the eye is least sensitive to you can get up to 348lm/W

[tabbypurr]

5w means 5w of heat, 35w means 35w of heat (very nearly). Cool white is cold looking, warm white is same light colour as filament lamps.

Led light is characterised by: lumens output (quantity) CCT (cool/warm/daylight) lumens per watt, efficacy And to a less significant extent beam width with spotlights.

NT

[whisky-dave]

sensitivity is how you react to ANY wavelengh of visable light.

So how can you equate that in wats of power from an LED you can't.

I've been loking this up for a student who couldn;t work out why he was only gettign 1ma from a solar panle he was holding up to our fl;oursecant light, he was expecting about 1/2 amp as that is what his panle was specced at bright light 1/2 amp at 12V he said he was getting the full voltage. Here in the lab at 4pm with the lab lights on he con sidered to be bright.

On measure I found it around 150 lumens, bright sunlight starts at around 30k lumens.

Yes because if we can't see it it;s not really light is it and pretty useless as a bulb of any type if the brightness is expressed in watts.

[Fredxx]

Hence the efficiency of lumens per watt is dependent on the spectra. For white light this is nominally fixed.

The articles I have given methods of working this out. Some even give examples of LED lamps.

Then I would say you are both probably getting confused with irradiance and radiance.

Quite

So at least we have established a theoretical conversion from LED output power in watts to lumens.