LED advice

[Pford75]

We are considering replacing some halogen downlighters (not installed by us!) with LEDs...for two reasons. Firstly, changing the bulbs is a pain as the ceiling is 14'6" and carting ladders into the room in question is not easy, secondly, there are a fair number of them and I am sure they are expensive to run.

Wonder if our resident experts could help me answer the following:

1. How many LEDs would be required for a room 5.4m x 5.4m (only one north facing window and high ceilings)
2. Does anyone have experience of the 15w LEDs available? (they seem very expensive)

 

[MdB]

I've never used LED lighting as I can't afford it but I'm sort of in the trade so keep an eye on them.

For the number you need, work in lumens - a filament 100W bulb is something like 1000-1200 lumens so work out how many 100W bulbs would give you the light you want and then compare this with the lumen rating of the LEDs you are considering.

Watch out however for the lifetime rating of high power LEDs you will find that some aren't as long as you might expect. To get the power output from LEDs, they often are run hot and heat kills the lifespan of LEDs. To this end, make sure you light fitting is suitable for the LEDs and won't cause it to overheat.

 

[chuckey]

Try this link : -http://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=5180&page=1#Item_0
Frank

 

[MdB]

http://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=5180&page=1#Item_0

Good stuff in there.

(Frank, the "-" at the front of your URL stopped in being clickable)

 

[Penners]

they seem very expensive

I disagree - with the "seem" anyway. :wink:

They're a ferocious price, particularly when you factor in the driver, too.

 

[Pford75]

Thanks all - very helpful

There does seem to be quite wide ranging opinion on whether retrofitting LEDs into GU10's is a great idea or a waste of time :?

Will let you know how I get on

 

[Flyfisher]

Watch out however for the lifetime rating of high power LEDs you will find that some aren't as long as you might expect. To get the power output from LEDs, they often are run hot and heat kills the lifespan of LEDs. To this end, make sure you light fitting is suitable for the LEDs and won't cause it to overheat.

That's interesting MdB, I'd assumed that the key virtues of LEDs were their cool running and long life, thus the expense was somewhat offset by the savings on maintenance and replacements.

When you say 'some' LED lighting can you be a bit more specific? Is it just the very high-power ones or does it apply to all of the white LEDs? Also, do you know if the reduced lifetime brings them into filament lamp lifetimes or is it still substantially better, albeit low for an LED?

 

[MdB]

"some" is for some individual white LEDs that didn't have a heatsink and had a lifetime in the thousands of hours mark rather than 10's of thousands hours but this is just from (a poor) memory. Having a quick look now at some data sheets, lifetime isn't specified at all on the parts I looked at (£0.30 sort of price) which isn't useful. Failure I believe is defined as when the brightness drops below 50% so they don't generally fail as such, it is just the light output that gets lower and lower.

I believe lifetime isn't generally a problem it is just something to watch out for at the cheap end of the market.

 

[Ixia]

I've been trying various LED GU10s and haven't been happy with the light quality at all, despite paying £25 for one of the bulbs. In fact our only success was a colour change LED, my 5yr old daughter loved it 8)

 

[AMc]

One very important thing to consider is the colour temperature of the light.
So called Bright White LEDs can create a very blue sort of mortuary colouring which is positively revolting.
In the old kitchen the previous owners had installed >500W worth of GU10 halogens switched in 3 arrays.
As the switches were across the room I replaced one array of two bulbs for £5 LED units from B&Q using 5W instead of 100W so we could leave them on and nip in and out without a problem. The light was absolutely horrible and if we hadn't been ripping it all apart anyway I would have gone back to the halogens.

I remember reading that the single LED with aluminium heat sinks were substantially better than the GU10 bulbs with an array of small LEDs but I didn't have much luck finding positive reviews for any of them that made me want to spend >£10 a bulb.

In the new kitchen we were required to use low energy lighting in dedicated fittings. Compliant fittings are deeper (to prevent the use of standard GU10 halogens) and on the recommendation of the electrician he fitted MegaMan CLFs. These are fine once they're going and have a good warm white colour temperature - however the warm up time is terrible sometimes taking minutes to achieve full brightness and I would only recommend them if you have a room you intend to keep lit for several minutes at a time - for nipping into the downstairs loo or the larder they are a constant source of irritation but at £10 a bulb I'm in no great hurry to switch them all.

I would recommend you only buy "warm white" LED bulbs and if they don't indicate colour temperature on the packaging and a lumen value not an equivalent wattage then I wouldn't waste your time. Incandesent bulbs are around 2500K and fluorescent tubes are around 4200K so you're looking for the lower number (not sure what the actual units are).

When I was looking for dimmable CLFs I was able to buy one for £10 at Homebase and test it before making the decision to replace all 4 in the lounge. The cost benefit of the bulbs meant I needed 15 months for a saving - and the bulbs carried a 12 month garranty - which I had to use on one bulb. They are now saving me money about 36 months later.

 

[MdB]

ncandesent bulbs are around 2500K and fluorescent tubes are around 4200K so you're looking for the lower number (not sure what the actual units are).

The units are Kelvin, i.e. what you call a cold blue light actually have a higher colour temperature.

Sunlight is around 6000K so is very blue compared to filament bulbs and bluer than the CFLs that people don't like.

 

[AMc]

ncandesent bulbs are around 2500K and fluorescent tubes are around 4200K so you're looking for the lower number (not sure what the actual units are).

The units are Kelvin, i.e. what you call a cold blue light actually have a higher colour temperature.

Makes sense I'm so used to seeing "K" as a kilo-something

 

[MdB]

Makes sense I'm so used to seeing "K" as a kilo-something

"k" meaning kilo-something should always have a small k.

(note I said should...)

 

[Flyfisher]

ncandesent bulbs are around 2500K and fluorescent tubes are around 4200K so you're looking for the lower number (not sure what the actual units are).

The units are Kelvin, i.e. what you call a cold blue light actually have a higher colour temperature.

Sunlight is around 6000K so is very blue compared to filament bulbs and bluer than the CFLs that people don't like.

. . . but isn't sunlight a much wider-spectrum light source whereas LEDs and CFLs have much narrower bands of light - which accounts for the very different 'feel' of such lighting systems?

I've never actually tried it but I'd not expect to get a complete rainbow of colours by passing LED/CFL light through a prism, as I would with sunlight.

 

[MdB]

. . . but isn't sunlight a much wider-spectrum light source whereas LEDs and CFLs have much narrower bands of light - which accounts for the very different 'feel' of such lighting systems?

Correct. However, your eye is a very poor spectrometer so can't tell the difference.

The point is the people complain about CFLs as they used to be bluer than filament (they aren't any more). The fact that sunlight is even bluer never gets mentioned due to the way that the eye perceives colour.

 

[philpjuk100]

I purchased a screw fit led and adaptor for night time use over a staircase,it gives a very blue light even though it said "daylight" on the packaging.I bought it in september last year and it stays on from around midnight until about 6/7 am.It has now started to turn itself off for periods of five or ten mins which is a pain,even though it is meant to be a very low wattage it runs quite warm,I cannot think the heat is coming from the led`s but there must be a transformer or resistor to drop the volts.When it finally dies (the off periods are getting longer) I will open it up to see how it used to work! but I will be replacing it with a cfl! phil (still typing with one finger!)

 

[Penners]

but isn't sunlight a much wider-spectrum light source...?

In my ignorance, I have always assumed that sunlight includes every wavelength of visible light, ultra-light and infra-light in the known universe. Isn't that the case?

 

[MdB]

As above, daylight = blue.

If your bulb is switching itself off now, then there is something wrong with it and I would be looking to replace it now.

 

[philpjuk100]

As above, daylight = blue.

If your bulb is switching itself off now, then there is something wrong with it and I would be looking to replace it now.

Yep that is the sensible thing to do but then I am not known for being sensible!(but as the wife sometime visits this forum I will replace it now!) phil.

 

[AMc]

I'd be a bit concerned about a mains powered device that was designed to be used while I'm asleep and is malfunctioning - I hope your smoke alarms work! :shock: Me, I'd swap it for a "Warm white" one now.

Daylight is "blue" and sunlight contains all the visible and invisible spectra of emissions. Sunlight is also many, many times stronger than any domestic light source (ask a photographer). Tungsten filament bulbs are yellow. Not sure about halogens but they have a particular spectral spread that makes things look bright - hence their use in retail and kitchens.

Digital cameras and camcorders have auto and manual white balance settings for each that adjusts what the sensor records as pure white in each circumstance. If you set your white balance to "tungsten" and take a picture outside it will have a heavy blue cast - if you set the camera to outdoor and use it without flash under tungsten lights you get a very orange cast.
The eye automatically compensates but the response to wavelengths of digital sensors is much narrower. Just as digital sensors struggle to deal with the variation in light levels that the eye can do without us even considering it.