How do white LEDs work?

Yes, I've googled it, but there are many different approaches. Which one is used in domestic LED bulbs?
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload
On Tue, 25 Apr 2017 12:25:35 +0100, "James Wilkinson Sword"
Ultra-violet LED exciting a white phosphor, much the same principle used in florescents.
--

Graham.
%Profound_observation%
  Click to see the full signature.
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload

That's what I would have assumed, but when you look at a switched off white LED, it's not white. I would have expected it to have a white coating that can be seen like on a switched off fluorescent tube.
--
When you want a man to play with you, wear a full-length black nightgown with buttons all over it.
Sure it's uncomfortable, but it makes you look just like his remote control.
  Click to see the full signature.
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload
On Tue, 25 Apr 2017 13:38:40 +0100, "James Wilkinson Sword"

Perhaps the phosphor just surrounds the die, with a clear epoxy envelope surrounding it.
--

Graham.
%Profound_observation%
  Click to see the full signature.
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload
On 25/04/2017 13:58, Graham. wrote:

I thought a thousand people would leap on this, but it's a blue LED with a yellow phosphor. Maybe not always, but as near as makes no difference.
Cheers
--
Clive

Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload


All that means is that it isnt white when it doesn't have UV falling on it and that the protective outer isnt the phosphor itself.

The difference is that leds don't have glass as the protective outer.
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload

Those adjustable-by-remote ones you have, just how many colours can you make? Do they only have R G and B emitters, or could you make a spectrum similar to sunlight?
--
"One dies in Istanbul suicide attack"

Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload
On 25/04/2017 13:27, Graham. wrote:

It is usually a high efficiency blue LED pump exciting a yellow phosphor with that mix determining the nominal colour temperature. It is quite peaky in the blue and more of a wide hump around the yellow. The phosphor usually looks yellow and sits on top of the LED.
http://i.stack.imgur.com/lkyXG.png
The visible light flux out of an LED die on a high efficiency LED these days is about the same order of magnitude as the sun's photosphere.
It is a lot more obvious on the devices which use a remote phosphor.
http://www.cree.com/led-components/media/documents/Remote-Phosphor.pdf
--
Regards,
Martin Brown
  Click to see the full signature.
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload

That's not as even as I thought. I thought they'd made it similar to the sun, which looks like this:
https://i.publiclab.org/system/images/photos/000/002/273/original/SunlightSpectrumGraph.jpg
Maybe we should be using the controllable colour RGB ones.

--
You never really learn to swear until you learn to drive.

Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload
On 25/04/2017 14:54, James Wilkinson Sword wrote:

They would be even worse at approximating the solar spectrum.
https://s-media-cache-ak0.pinimg.com/originals/b4/e8/0f/b4e80f3c5baf7e5d4ad09e07cc796e89.jpg
RGB LED emissions have a fwhm of 50nm so would have a very peaky spectrum. It doesn't normally matter except for colour matching or where you have unusually narrow band pigments.
Materials that have very different colour depending on the white light source you use are called after the semiprecious stone Alexandrite.
https://en.wikipedia.org/wiki/Chrysoberyl#Alexandrite
The other common one is neodymium doped glass used by glassblowers to see into a gas flame against the yellow-orange glare of sodium emission.
--
Regards,
Martin Brown
  Click to see the full signature.
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload

Actually, they seem to be sold as RGBW, so they probably ave white LEDs too. But you can add a bit of R G B as necessary to make it closer to sunlight or whatever tone you prefer.
Clearly the best thing would be a phosphor mix that makes precisely the levels you get from sunlight, or many different wavelength LEDs which can be individually adjusted by the user to give the preferred output.

--
The opposite of courage in our society is not cowardice, it is conformity; and there you have the trouble today is conformity: People acting like everyone else without knowing why, without knowing where they're going. -- Earl Nightingale

Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload
wrote:

That's for brightness reasons.

Yep, that's what they do.

There is no such animal. Sunlight varys tremendously.
The sunlight you get on that soggy little frigid island is nothing like what we get here.

Yep, that's what the best of the led bulbs do, so you can have any color temp you like, and different color temps at different times too.
Considerably more expensive to do it that way tho.

Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload

So you can create a very even spectrum like with sunlight?
Give me a link to such a bulb, I want to try one.

When the sky is blue, I would think it's similar everywhere all over the globe. Just a different intensity.

--
Connecticut police are investigating a string of shootings where clues are reportedly contained in a rap CD.
They are also questioning Bob Marley about the shooting of a sheriff.
  Click to see the full signature.
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload
wrote:

Nope, that's very difficult to do with leds.

Fraid not. And you don't get the same blue sky everywhere either.

Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload

Surely you can at least make the R G and B frequencies that the LEDs produce be the right levels for sunlight?

Cite?
--
She was as easy as the Daily Star crossword.

Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload
James Wilkinson Sword wrote:

Long thread. How many wanks will you get out of this one, you little piece of benefit claiming shit?
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload
wrote:

Yes, but the SPECTRUM is nothing even remotely like real sunlight.

Don't need a cite, look at the photos.
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload

But it has to be an improvement over white LEDs.

Never seen a difference.
--
Say it with flowers - send her a triffid.

Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload
On Tue, 25 Apr 2017 14:27:29 +0100, Martin Brown wrote:

An interesting read (note the use of the expression "loosing efficiency" on page 8 regarding Fig 7a). Also of note is the copyright date of this document which is the year of their record breaking 303Lm/W led efficacy achievement in February/March of that year when the Cree Spokesperson let slip to the trade press that such laboratory achievements typically took a further 18 to 24 months of development before making their début on store shelves for public consumption.
A simple arithmetic calculation reveals that this scheduled development has slipped by a rather conservatively estimated 13 months. :-( The best Lm/W efficacy figures I've noted recently have been around the 125 to 145 Lm/W mark. The former being a 1500Lm 12W GLS B22 2700K Warm White lamp I sampled from a Home Bargains store for the princely sum of £2.99 which turned out to have an *actual* consumption figure of 14 watts.
Since its illumination power doesn't seem as impressively bright as I was expecting (even making allowances for the eye's logarithmic response to brightness), I rather doubt the additional 2 watts is hiking the claimed 1500Lm to 1750Lms as one might expect if the additional 2 watts was simply the result of overly wide tolerances in the 'electronic ballast circuit' causing the LEDs to be overdriven to a higher than designed Lumens output.
I have a sneaking suspicion that the claims of "1500 Lumens at 12W (100W eqv)" have been based on the best of a sampling of these lamps off the production line, possibly based on the maximum positive tolerance limit of the 'nominal' power consumption to boot for good measure (+10%? 13.2W) so might more typically be nearer the 110Lm/W mark than to the claimed 125Lm/W figure. Even the claimed efficacy is not a particularly massive improvement over the 81Lm/W efficacy figures typical of many LED GLS lamps of just over three years ago.
The 145Lm/W lamps I saw were the grossly overpriced 1600Lm LES 11W examples being offered by Asda. I might have considered buying one if they'd been more sanely priced but at something like 10 to 18 quid a pop (I didn't bother trying to pin the confusing shelf price labelling down any tighter than that - it was enough to know that it was at least 3 times pricier than I'd been prepared to pay in Home and Bargain), I wasn't in the least bit tempted.
It's not so much the electrical consumption cost savings that interest me so much as the service life endurance promise standing a much better chance of being fulfilled outside of a laboratory test environment in the more demanding conditions typical of a domestic pendant light fitting complete with fancy draught excluding shade dangling in the warmest layers of air to be found in a room basking in the warmth of a centrally heated radiator or two.
I'm happy enough with the current crop of "60W 806Lm 120v 750 Hour life rated" American tungsten GLS lamp equivalent 9W LEDs where an 806 Lm lamp can provide the required illumination level (effectively replacing a 73W 240v 1000 hour tungsten filament GLS lamp in UK housing). It's all these 15 and 18 watt 1500Lm LED GLS replacements for the 100W tungsten filament GLS lamps with their more marginal temperature tolerance that give me pause in their deployment as a GLS alternative.
The LED version of the "100W GLS tungsten filament lamps now starting to appear would seem to be a viable GLS candidate if their claimed efficacies of 145 and 150 Lm per watt are based in reality rather than best hoped for efficacy.
It's been a rather disappointing wait for Cree to begin fulfilling that (probably ill advised) promise made by their spokesperson just over three years ago when they announced their record breaking achievement in LED efficacy. Here we are, some 50 percent further along than their upper timescale to get 300Lm/W lamps to market, with lamps of only half that efficacy to show for their efforts thus far.
Still, at least *some* progress has finally materialised at long last, so I suppose we ought to be grateful to finally be free of the 2013 'Time Warp' we seem to have been living in for the past 3 or 4 years. :-) Better late than never.
At this rate of development, we'll be lucky to see the next efficacy milestone of 200Lm/W being achieved within the next three years or so. Who knows? We may see a sudden spurt from Cree whereby the 200Lm/W milestone in commercially available lamps is reached within the next 12 months. Either that or else an admission that the 303Lm/W lab results were faked just to pressurise Philips Lighting into quitting the LED lamp business. :-(
--
Johnny B Good

Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload

ch

hor

se

f

cy"

s

cy

let

ok

n

nt

st

145

I

ch

I thought the best LEDs were equivalent to 10W out per 1W in. Eg a 10W LED bulb should be equivalent to a 100W incandescent. A 100W incandescent is 1435 lumens. So your bulb is consuming 14W to give out about 105W. Not as good as I thought.

se

s

00W

t

y

ED

Companies lie, they always do. Cameras state x MP, and if you take a photo at full resolution, it's shit. Hard disks don't use gigabytes, but billions of bytes, shaving off a little.

op

n

I'm currently using this sort of thing: http://www.ebay.co.uk/itm/231644564446 Might not be the best price, I just linked to the first one I found, not where I bought them from. The LEDs are well spaced and they don't exceed body temperature, so they don't fail like most LED bulbs.

r

the

ly

fe

amp

3W

se

ent

to

at

ree

ime

2

amp

They really should put sensible ratings on each LED bulb they sell. It should clearly state the actual electrical consumption (it's been mentioned in this thread that they lie), and equivalent output (eg "=60W incandescent". The general public don't know what a bloody lumen is.
-- I took a vow of faith, I don't shoot any more. You don't shoot any less either. -- Machete, film, 2010.
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload

HomeOwnersHub.com is a website for homeowners and building and maintenance pros. It is not affiliated with any of the manufacturers or service providers discussed here. All logos and trade names are the property of their respective owners.