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Conversion efficiency of White LED backlights

P

PeteS

Jan 1, 1970
0
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
 
J

John Woodgate

Jan 1, 1970
0
dated said:
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 ;)

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'.(;-)
 
I

Iwo Mergler

Jan 1, 1970
0
PeteS said:
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 ;)
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
 
P

PeteS

Jan 1, 1970
0
John said:
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'.(;-)
--
OOO - Own Opinions Only. Try www.jmwa.demon.co.uk and www.isce.org.uk
2006 is YMMVI- Your mileage may vary immensely.

John Woodgate, J M Woodgate and Associates, Rayleigh, Essex UK

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
 
J

John Woodgate

Jan 1, 1970
0
dated Thu said:
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.

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

PeteS

Jan 1, 1970
0
John said:
The black screen and the enclosure allow some heat to escape, by
convection and radiation. The latter is not negligible at low
temperatures.
--
OOO - Own Opinions Only. Try www.jmwa.demon.co.uk and www.isce.org.uk
2006 is YMMVI- Your mileage may vary immensely.

John Woodgate, J M Woodgate and Associates, Rayleigh, Essex UK

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
 
B

BobG

Jan 1, 1970
0
PeteS said:
I simply wondered if anyone knew the conversion
efficiency so I could tweak the heat dissipation map for the device :)
=====================================
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.....
 
J

John Woodgate

Jan 1, 1970
0
dated said:
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 :)

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?
 
P

PeteS

Jan 1, 1970
0
John said:
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?
--
OOO - Own Opinions Only. Try www.jmwa.demon.co.uk and www.isce.org.uk
2006 is YMMVI- Your mileage may vary immensely.

John Woodgate, J M Woodgate and Associates, Rayleigh, Essex UK

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
 
P

PeteS

Jan 1, 1970
0
PeteS said:
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

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

Cheers

PeteS
 
K

Kevin White

Jan 1, 1970
0
BobG said:
=====================================
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....

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:http://en.wikipedia.org/wiki/Light_bulb#Luminous_efficacy_and_efficiency
http://www.otherpower.com/otherpower_lighting.html.

kevin
 
C

colin

Jan 1, 1970
0
Kevin White said:
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:http://en.wikipedia.org/wiki/Light_bulb#Luminous_efficacy_and_effici
ency
http://www.otherpower.com/otherpower_lighting.html.

kevin

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

Colin =^.^=
 
G

GregS

Jan 1, 1970
0
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:http://en.wikipedia.org/wiki/Light_bulb#Luminous_efficacy_and_efficienc
y
http://www.otherpower.com/otherpower_lighting.html.


Kevin WHITE !!

Thanks for the info.

greg
 
J

James Waldby

Jan 1, 1970
0
Kevin said:
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.
....

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 http://www.ledjournal.com/ .) 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
 
G

GregS

Jan 1, 1970
0
....

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 http://www.ledjournal.com/ .) 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...

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
 
G

GregS

Jan 1, 1970
0
....

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 http://www.ledjournal.com/ .) 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...

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

greg
 
D

Dirk Bruere at NeoPax

Jan 1, 1970
0
Kevin said:
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.

last time I looked Luxeons were about 40 lumens/watt
 
D

Don Klipstein

Jan 1, 1970
0
last time I looked Luxeons were about 40 lumens/watt

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 ([email protected])
 
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