Will future LEDs have build in Peltier coolers?
It seems to me the heat will have to go somewhere... so the outside will be even hotter... Maybe it will help though. Efficiency? Probably not so good.
Will future LEDs have build in Peltier coolers?
It seems to me the heat will have to go somewhere... so the outside will be even hotter... Maybe it will help though. Efficiency? Probably not so good.
I don't know about that, but I read the theoretical efficiency of LEDs is
683 lumens per watt. The best efficiency at this point seems to be between 10% and 20%. I thought they were much better than that. What's the holdup in the technology and is there a practical limit the efficiency of LEDs? Mike
The coolers are mostly for laser diodes, which have to be run at a constant temperature if you want to avoid mode-hopping (if the temperature moves by more than a few degrees) or the output wavelength and beam direction changing with temperature - both tend to move in proportion to the temperature change between mode-hop points.
The Peltier junction-based thermostat I developed and published was used to stabilise the temperature of an optical stage to +/-0.001 degrees Celcius, which was a bit of an overkill - our noise floor was roughly equivalent to 0.01 degrees Celcius. My successor value- engineered the circuit and used it to control the associated diode laser to +/-0.01 degrees Celcius to avoid mode-hopping and to keep the beam direction constant.
Illumination LEDs have to be much cheaper and certainly couldn't carry the overhead of a Peltier cooler. They probably couldn't even carry the overhead of a heat pipe, which would probably do everything that the designers would end up asking of a Peltier cooler.
-- Bill Sloman, Nijmegen
On a sunny day (Fri, 11 Jan 2008 08:04:49 -0800 (PST)) it happened snipped-for-privacy@ieee.org wrote in :
That is fantastically accurate, .001 C, better not breath on it.
Well, the high power white LEDs are still very expensive atm, so if more light could be generated (but I am not sure about that) by keeping those cooler, maybe in that market segment? Of course I agree, a better heat sink, or heat pipe would do the same or more, as it uses no additional power.
It has to go somewhere. For most uses a Peltier is impractical.
I just saw a new laser that illuminates instantly. Another SS Laser i was working with took time to warm up the diode before it turned on. I'm sure that was a better system. After turn on there was not that much heat generated at the sink and it was a 100 mw unit. I was trying to get the tube laser working. Talk about heat !! I'm glad the SS one will work. The efficiency difference between the tube and SS is amazing.
greg
is
=A0 =A0 =A0 =A0 Mike
The theoretical maximum ouput per watt of *any* lightsource depends on the wavelength of the light produced - at 555nm it is 683lm per watt - and is less than this at all other frequencies. This is not a LED specific property in any way but is rather a property of visible e-m radiation. Depending on the particular colour 'white' in question it is around
298 lm per watt.
Hello Jan,
I hope the lm/W efficiency will increase in the future and or the total radiated power/W. This would reduce the heat to be removed and saves the power for heat removing. A while ago I was surprised that HP has some green LEDs that claim an efficiency of 484lm/W (as 683 is the theoretical maximum for 555nm light).
I know of thermal problems in LED light bulbs for domestic use. Probably white fluorescent sources still have higher lm/W rating than many LED lamps.
Best regards,
Wim PA3DJS
Ds is
=A0 =A0 =A0 =A0 Mike
Why would it be less at all other frequencies for "any lightsource"??
LEDs is
=A0 =A0 =A0 =A0 =A0 Mike
The lumen is defined in terms of our reaction to light - it measures perceived illumination, and is adjusted for the varying sensitivity of the human eye to different wavelengths of light - apparently the cone response at normal light levels.
The rods are reported to be more sensitive to the blue end of the spectrum, and someone does seem to be trying to sell light sources that take advantage of this
-- Bill Sloman, Nijmegen
We could have done a little better if we'd put some more effort into it. The best thermostat I've read about for room temperature specimens did a lot better - +/-3.5uC - but that was a well insulated and well stirred tank of water, with a thermal time constant of eight hours, and the performance was probably limited by the Johnson noise in the sensor. I think they could have done better with a sensor had that was in much better thermal contact with the water in the tank, but putting such a sensor together would be something of a performance.
-- Bill Sloman, Nijmegen
is
The lumen is defined in terms of our reaction to light - it measures perceived illumination, and is adjusted for the varying sensitivity of the human eye to different wavelengths of light - apparently the cone response at normal light levels.
The rods are reported to be more sensitive to the blue end of the spectrum, and someone does seem to be trying to sell light sources that take advantage of this
Well, yes, but I think you have confused "maximum output" with "maximum perceived output". Lumens are important for a display or indicator, but not for other applications, such as driving power into a fiber or a non-human detector. It seems to me that you have mixed up the energy-absorbing power of the human visual system with the electricity-to-light conversion effiiency of an LED.
683 lumens per watt is the theoretical efficiency for the green wavelength at which human photopic vision has highest sensitivity. This figure is less for all other visible wavelengths.
There are already white LEDs on the market that appear to me to be at least about 25% efficient, probably more like about 30%. This figure increases somewhat when they are moderately underpowered (100 mA for ones with 1 mm^2 dice).
As for losses:
The phosphor does not have 100% quantum efficiency - some blue photons are absorbed and fail to result in red/orange/yellow/green photons being emitted.
The red/orange/yellow/green emitted photons also have less energy than the blue photons that are "converted" into the longer wavelength ones. That energy loss per photon from the "conversion" is known as the "Stokes Loss" and is somewhere around 20% for the phosphor in the usual white LEDs. (This is in addition to the phosphor loss from blue photons failing to produce red/orange/yellow/green ones.)
- Don Klipstein ( snipped-for-privacy@misty.com)
That high lumen/watt figure is the conversion factor to translate between radiometric units and photometric units for the output of this LED. Many HP/Agilent/Avago LED datasheets have this figure. This figure is one for a property (luminous efficacy) of the emitted light, not overall luminous efficacy of the LED in lumens out per watt of electricity in.
If this is multiplied by the efficiency of the LED at converting electricity to light, then you get lumens out per watt in.
- Don Klipstein ( snipped-for-privacy@misty.com)
In , I, Don Klipstein wrote in part:
^^^
I meant to say "die" - which is the rectangular/square chunk of semiconductor material that is also often called a "chip".
- Don Klipstein ( snipped-for-privacy@misty.com)
Maybe use IR LEDs with negative current so it will cool itself (darn! not April 1st!)?
On a sunny day (Sat, 12 Jan 2008 06:11:30 +0000 (UTC)) it happened snipped-for-privacy@manx.misty.com (Don Klipstein) wrote in :
I had some fun here shining a blue LED on a white unpowered LED. Indeed then the unpowered one lights up white
On 12 ene, 07:16, snipped-for-privacy@manx.misty.com (Don Klipstein) wrote: [deleted]
Hello Don,
Thank you for the update. The value specified appeared to me exceptionally high. So because of (radiant power)/(electrical power) far below 1, overall efficiency will probably drop below 60lm/W (input power).
So I can better keep the high efficiency tubular fluorescent lamps with electronic ballast. . . .
Best regards,
Wim PA3DJS
The lumen is defined in terms of our reaction to light - it measures perceived illumination, and is adjusted for the varying sensitivity of the human eye to different wavelengths of light - apparently the cone response at normal light levels.
The rods are reported to be more sensitive to the blue end of the spectrum, and someone does seem to be trying to sell light sources that take advantage of this
-- Bill Sloman, Nijmegen
Thanks Bill, Very interesting article about the lighting temperature, now how do I apply the findings. On last visit with my mother she was ready to give up her internet connection because it caused to much eye strain. Well, I'm sure some of that was caused by her very slow dialup connection, cable connection is soon to be installed. First I'll give my limited understanding of what I read. With higher temperature light the rods react causing the pupil to close down, then, from the article; "smaller pupils provide better acuity, improve the depth of field, and allow less accommo-dative response of the eye " Because of the higher temperature the closeing effect of the pupil happens at lower light levels. with lower light level there is less glare caused both outside and inside the eye. This inside the eye glare might be some of my mothers problem, she has had one cateract removed and not ready to have the other one done yet. So, 1) I get a higher temperature light source 2) Where do I put the light source? Above and behind her sitting position? Behind the monitor lighting the wall? Thanks for your input, Mike
I have done that also. Some white LEDs also glow from blacklights. Usually, the glow looks yellowish to me.
- Don Klipstein ( snipped-for-privacy@misty.com)
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The first question about your mother's monitor is whether it is a self- luminous cathode ray tube monitor, or a liquid crystal display that depends on reflected light.
With the cathode ray tube, the best bet would be to reduce the ambient light levels - any ambient light reflected from the surface of the monitor is purely glare, and a bright lamp above and behind her sitting position could be dumping loads of uninformative and irrelevant photons onto her retina.
With a liquid crystal display, the situation can slightly more complicated. If the display has a back-light, the situation is much the same as for a cathode ray tube based monitor and you want to minimise the number of uniformative photons being reflected into her eyes by the top surface of the display.
If the display isn't back-lit, the reflected light provides the information about the status of each pixel in the display, and you want to maximise the number of photons coming over your mother's shoulders and hitting the screen square on. Liquid crystal displays are best viewed square on - the contrast ratios tend to drop as the light hits screen further away from normal.
It may be useful to turn your mother's monitor off and look at the blank screen to see if you can see reflections from any of the room lights.
-- Bill Sloman, Nijmegen
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