Conversion efficiency of White LED backlights

Well, my LCD supplier has decided they can put a white LED backlight onto the panel size I use. Now I'm trying to get a reasonable thermal budget, and something I am trying to find out is the typical conversion efficiency ( electrical energy -> light ) of the backlight.

Details: 3 x string of 8, Vf 27V typical at 25mA

I currently don't have a panel here (it seems to be taking a slow boat from Taiwan) and I'd like to get a head start so I can do some rough placement planning and I wondered if anyone here had any knowledge of said conversion efficiency.

Obviously, energy not converted to light gets converted to heat and I'd like to get a handle on what I need to deal with. This is a handheld XDA device, so thermal management is sorta important ;)

Cheers

PeteS

Reply to
PeteS
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In message , dated Thu, 17 Aug 2006, PeteS writes

Initially, while you are waiting for the slow boat, assume zero efficiency and calculate on that. If you don't find a problem, you don't need to know the efficiency. It's called 'engineering'.(;-)

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Reply to
John Woodgate

Energy not *escaping* as light gets converted into heat. If the display shows a black picture, almost nothing escapes. So, for the worst case, practically all energy gets transformed into heat.

Kind regards,

Iwo

Reply to
Iwo Mergler

Snort

I did that ;)

Total power consumption for a 5.7 inch panel at full brightness comes out at just over 2W, which isn't *that* bad - provided I am careful with everything it will maintain the distributed nature of the heat and keep the temperatures low enough so I can charge My Li+ batteries.

Cheers

PeteS

Reply to
PeteS

In message , dated Thu, 17 Aug 2006, Iwo Mergler writes

The black screen and the enclosure allow some heat to escape, by convection and radiation. The latter is not negligible at low temperatures.

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Reply to
John Woodgate

I might have noted in the first place that I can live with 2W of dissipation and there is, of course, some heat escape via convection and radiation. I simply wondered if anyone knew the conversion efficiency so I could tweak the heat dissipation map for the device :)

Cheers

PeteS

Reply to
PeteS

===================================== I heard a rumor they were 'almost as efficient as compact flourescents', but since I don't know how efficient THOSE are, I guess I can't help.....

Reply to
BobG

In message , dated Thu, 17 Aug 2006, PeteS writes

The information is out there; I thought you wanted a way to progress without waiting for it to appear. Won't the manufacturer tell you?

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Reply to
John Woodgate

The answer was 'we are still characterising the device' - which is of course a euphemism for 'we don't know'.

I have already designed assuming zero efficiency, and I'll find out when I measure the damn thing in about a week or so.

Cheers

PeteS

Reply to
PeteS

The bright side of this (no direct pun intended) is I will actually report my findings once I test the units ;)

Cheers

PeteS

Reply to
PeteS

White LEDs are only about 3% efficent, 15-20 Lumens/watt - about the same as incandescent lamps. CFL produce about 60 Lumens/Watt. A lamp with 100% efficiency would produce 600-700 Lumens/Watt.

For your application nearly all the electrical power would be converted to heat - a large proportion of even the small amount emitted as light would be converted to heat within the LCD display.

See for example:

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kevin

Reply to
Kevin White

example:

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ency

It is rather dissapointing how inneficient they are given the hype about their efficiency.

Colin =^.^=

Reply to
colin

Kevin WHITE !!

Thanks for the info.

greg

Reply to
GregS

...

Several DOE-funded research projects are aimed at 50-80 lumens/watt LED's. Eg, Color Kinetics Inc. aims at 80, Eastman Kodak aims at 50, Osram Sylvania aims at 80. (See page 4 of Summer 2006 LED Journal. Magazine's web page is

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.) Also, CAO Group Inc. claims to be getting 50-70 lumens/watt in Dynasty 640 white LED's on page 8 of same issue -- perhaps fueling the rumors...

-jiw

Reply to
James Waldby

Edmund Scientific made an anouncement some time ago about increasing the lamp market share with high intensity LED's using some kind of fiber optic conversion. I think mostly for projection type lamps.

greg

Reply to
GregS

Phillips 3 W K2, manufacurer says up to about 47 lumins from 1 watt. They are hard to get right now.

greg

Reply to
GregS

last time I looked Luxeons were about 40 lumens/watt

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Reply to
Dirk Bruere at NeoPax

100% efficiency of producing a yellow-green at a frequency of 540 THz (wavelength approx. 555 nm) is 683 lumens per watt by definition. Human photopic vision peaks there. 100% efficiency of producing white light varies, depending on the definition of white light. But for "white light" to be the 400-700 nm portion of the spectrum produced by most white artificial white light sources, 100% would usually be somewhere around 250-300 lumens/watt.

- Don Klipstein ( snipped-for-privacy@misty.com)

Reply to
Don Klipstein

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