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News and links! UPDATE 5/14/2010
General Notes and Disclaimers
Pure Red / Deep Red LEDs
- 14 to 15 lumens/watt
Orangish Red LEDs - 46-55
lumens/watt
Red-Orange LEDs - 53-75
lumens/watt
Truly Orange LEDs - 18-22
lumens/watt
Yellow and "amber" LEDs -
22-63 lumens/watt, with a way for 40-100 for less-amberish yellow.
Yellow-Green LEDs - 8
lumens/watt, but there is a way to get 80.
Green LEDs - 58-79
lumens/watt.
Better InGaN green LEDs get 90-120-140 lumens/watt at 1.7-3
milliamps
Blue-Green LEDs - 50-65
lumens/watt
Blue LEDs - 17-29 to
optimistically 30 lumens/watt
White LEDs - 48-100-120-150
lumens/watt.
Increased Efficiency of InGaN LEDs at lower currents
Important Notes on Gallium Nitride and InGaN LEDs!
LEDs with high candela "beam candlepower" figures
LEDs with high total lumen output
Notes on Where To Get Efficient LEDs
Converting / comparing lumens, candelas, millicandelas
UPDATE 5/14/2010 - Cree announced in this 5/10/2010
press release a 2 by 4 foot LED light fixture (LED luminaire) that
achieves 100-plus lumen/watt overall luminous efficacy from AC line voltage
electrical input to light exiting the luminaire. Cree's LR24HE achieves this
even with color temperature of 3500 K and color rendering index of 90.
Light output is said to be 3200 lumens, which I figure to be around 56-76%
of that of most 2-lamp 4-foot fluorescent fixtures.
Cree mentions this LED light fixture being shown at their booth at
Lightfair 2010.
UPDATE 4/30/2010 - Cree announced in this 4/12/2010
press release that they expect fall 2010 production availability of their
XLamp XM LEDs. These are expected to achieve 160 lumens/watt at 350 mA, and to
achieve 110 lumens/watt at 2 amps, producing 750 lumens from less than 7 watts.
I suspect that the die (chip) may be larger than the usual roughly 1 mm square.
However, I am expecting that more likely the overall luminous efficacy will be
near or over 125 lumens/watt both at current density of 350 mA/mm^2 and at
1 amp. This press release does not mention the size of the die.
UPDATE 2/14/2010 - Cree announced in this 2/3/2010 press release that they achieved a white laboratory prototype LED that achieved 208 lm/W at 350 mA. Output was 208 lumens, indicating a voltage drop of 2.86 volts. Correlated color temperature was reported to be 4579 K.
UPDATE 5/18/2009 - Cree has issued this 4/30/2009 press release announcing thay they were demonstrating at LIGHTFAIR on 5/5-7/2009 their XP-G LED, producing 139 lumens with overall luminous efficacy of 132 lumens/watt at 350 mA. Forward voltage at 350 mA works out to 3.05 volts.
UPDATE 11/28/2009 - 3M achieved a green LED achieving 181 lm/W at 350 mA by combining a green-emitting phosphor with an available blue LED chip. This is mentioned in this 11/23/2009 item in LEDs Magazine.
UPDATE 7/22/2008 - Osram was noted in this 7/21/2008 LEDsMagazine Article that they achieved a laboratory prototype LED delivering 136 lumens/watt and 155 lumens from a high power LED operating at 350 mA. This translates to 1.14 watts and voltage drop of about 3.26 volts.
Notably, the correlated color temperature is lower than usual for most white LEDs - 5000 Kelvin. Also notable is that the chromaticity coordinates (presumably on the 1931 CIE chromaticity diagram) are x,y of (.349, .393). This is a significantly greenish shade of white.
Further notably, this article shows this LED having a characteristic of overall luminous efficacy increasing as current is decreased for all currents greater than approx. 30 milliamps. Overall luminous efficacy peaks at approx. 170 lumens/watt when current is around 25-30 milliamps. I find that in general white LEDs have overall luminous efficacy varying a little inversely with current/power throughout the range of "moderate to moderately severe underpowering" to the maximum current/power possible.
UPDATE 11/2/2004 - WITH THANKS TO FANS OF THIS WEBSITE:
In August 2004, Osram announced a prototype of an orange-red LED that achieved 108 lumens/watt, producing over 2 lumens at 10 mA with a voltage drop presumably of about 2 volts.
Look in This Osram Press Release.
UPDATE 12/1/99 Agilent (now Avago) has improved models working in the lab. Odd
shaped LED dice such as a truncated inverted pyramid let more light out than
rectangular ones by reducing the amount of light trapped by "total internal
reflection". Such dice are now used in some Lumileds "Luxeon" red, orange and
yellow LEDs - namely those with the "Lambertian" radiation pattern, which are
their "High Dome" ones.
Look in
http://www.photonicsonline.com/read/nl19991130/39722
for details including claims of overall luminous efficacy as high as 102
lumens/watt for orange and 68 lumens/watt for orange-amber.
Compound Semiconductor magazine (the May/June 2000 issue) has mentioned surface texturing to increase efficiency. This seems to be another approach to reduce total internal reflection trapping of photons. Total internal reflection is a serious issue in many LEDs due to the extremely high refractive index of some LED materials.
IMPORTANT NOTE Many laboratory prototypes mentioned above are not yet in production even if years old! Barriers apparently include but may not be limited to patents held by competitors! Also, gallium nitride based LED chips just may not be cheap (substrate material is generally about 9 on the Moh's hardness scale where diamond is 10). Production of chips of size favoring a more optimum current density may price such things out of the market more than improve efficiency.
Some brands mentioned here as achieving efficiencies less than those of the best mentioned here but without recent updates mentioned may have since improved.
Luminous efficacies were largely determined by one or more of several methods,
mostly almost laughably crude. I give NO warranty as to accuracy. I have at
times slightly changed my estimates for some models. Your mileage may vary.
Unless otherwise noted, luminous efficacy is stated for a 25 degree Celsius
(77 degree F.) ambient with a current of 20 milliamps (350 mA for heatsinkable
models) in an environment that does not build up heat around the LED.
Heatsinkable models are generally stated to achieve their claimed performance
when cooling is sufficient to cool either the heatsinkable surface or the
junction temperature to 25 degrees C.
Red, orange, yellow, and yellow-green models (other than high power /
heatsinkable ones) mentioned here generally have maximum efficiency at
currents around 20-25 milliamps. Efficiency of these is typically less at low
currents of a few milliamps or less. The decrease is not as bad with GaAlAsP
and "T.S." AlGaAs and the most efficient InGaAsP red ones as it is with most
other InGaAsP (orangish red through yellow-green).
Indium gallium nitride types (most ultrabright blue, blue-green,
non-yellowish green, and white types) usually have efficiency that increases
with decreasing current, although the increase will reverse as current
decreases below something like 2 mA or a fraction of rated current.
Please beware that performance of many LED models at currents below a few tenths
of a milliamp or a percent or so of maximum rated current may be unreliable.
There may be significant tolerance in light output. Your mileage may vary.
Some of these LEDs radiate light of slightly different colors in different directions. This is most apparent with many white models and narrow-beam yellow models, as well as the most efficient yellow-green models.
PLEASE NOTE that the lumen per watt figures in this document are lumens of light produced per watt of electricity delivered to the LED. Some LED manufacturers state much higher figures indicating the lumens per watt of radiated light. The latter, high figure is typically in the ballpark of 60-100 for red, 130-180 for orange-red, 220-265 for red-orange, 440-500 for yellow, 400-plus to near 660 for green (656 for Avago HLMP-C115), and around 50-90 for blue. The main purpose of this "high" figure is for conversion between radiometric and photometric units for the emitted light. If the conversion efficiency and the "high" lumen/watt figures are both known, multiply them to get the lumens out per watt in.
Beam brightness and width figures below are mostly ones claimed by manufacturers/distributors and I have NOT confirmed most of these.
UPDATE 5/11/2009: LEDEngin makes some deep red high power LEDs, available at Mouser Electronics. These LEDs have rated peak wavelength of 655-670 nm, typically 660 nm. These appear to me to use GaAlAsP chemistry and to be unusually efficient for GaAlAsP.
The LEDEngin LZ4-00R210, LZ4-20R210 and LZ4-40R210, at 700 mA, are claimed to have typical voltage drop of 10.5 volts and typical radiant flux of 1.8 watts. This is typical efficiency of 24.5 percent.
One update of mine is that spectral analysis indicates dominant wavelength of 643-644 nm and luminous efficacy of the emitted light to be about 60 lumens/watt. If radiometric efficiency is indeed 24.5%, then overall luminous efficacy is 14-15 lumens per watt.
Other LEDEngin high power deep red LEDs achieve efficiency similar to or slightly lower than that of LZ4-00R210, LZ4-20R210 and LZ4-40R210.
Red LEDs with GaAlAsP and Avago's similar AlGaAs in my experience, when doing well, tend to achieve 7-8 lumens per watt. But unlike the more efficient orangish red ones below, they are truly fairly pure red in color, with dominant wavelength (color specification roughly meaning hue) of 637-648 nm, usually 640-645 nm, and peak wavelength of 645-665 nm, usually 660 nm.
Radio Shack red LEDs of this chemistry include 276-086, 276-087 and 276-307.
These "automotive" red LEDs are orange-red ones even slightly more orangish than the ones below in this "orange red" category. These have a typical dominant wavelength of 620 nm, roughly "taillight orange-red".
The following orangish-red LEDs have typical dominant wavelength stated to be 623 to 627 nm, which often appears to be an orangish red but sometimes appears "plain red", especially when background is white light with color temperature at least 4100 K. Avago (formerly Agilent, formerly to that HP) LEDs in this category have been stated to have typical dominant wavelength of 630 nm, but my experience is that a few years ago the dominant wavelength appeared to me to have shifted from about 631 nm to somewhere in the mid-620's when their efficiency increased from near/below 20 to mid-upper 20's lumens/watt.
UPDATE 10/12/2009: Osram LS E65F-BBDA-1-Z, in stock at Digi-Key, at 50 mA typically achieves 41.7 lumens/watt. According to its datasheet, typical performance at 50 mA is 4.48 lumens with forward voltage drop of 2.15 volts.
UPDATE 1/1/2008: The most efficient "low power" red LEDs I tested so far are a batch of Nichia NSPR510CS ones I just got. Most units in this batch achieve about 46 lumens/watt at 20 mA according to my tests. Forward voltage drop averages 1.95 volts and light output averages 1.8 lumens according to my testing.
UPDATE 10/30-2005 - I recently purchased some Avago HLMP-ED33-SVOOO LEDs from Digi-Key. These achieved a good 28 lumens per watt, possibly 30. With this efficiency advancing so slowly in recent years and tight competition between at least some brands in achieving this efficiency in recent years, I do expect some LEDs of some other brands to achieve similar efficiency.
Avago HLMP-E*** types mostly come in 2-3 brightness-sorted subtypes.
UPDATE 10/9/2003 - I just received some samples of ETG's ETG-5TS630-30. Results: Around 28 lumens/watt.
UPDATE 7/4/2003 - Now for high power red LEDs: *Test Results* Lumileds LXHL-MD1D Luxeon Stars (5 pieces tested) test as averaging 35 and give or take a few lumens/watt at 325 mA. The figure I am using for lumens per radiated watt may be low for these. The average for this product may indeed be higher - the datasheet indicates typically 44 lumens at 350 mA with a typical voltage drop of 2.95 volts, or 42.6 lumens/watt - though when the junction temperature is 25 degrees C. The datasheet also indicates, according to my interpretation, that output and efficiency are about 22% less when the heatsinkable surface of the LED is at 25 degrees C than when the junction is at 25 degrees C.
UPDATE 1/26/2009 - Lumileds LXK2-PD12-R00 typically produces 45 lumens at 350 mA with a typical voltage drop of 2.95 volts. This works out to 43.6 lumens/watt, at a junction temperature of 25 degrees C. I would expect 11% less when the heatsinkable surface is at 25 degrees C, due to the thermal resistance figure and the output-vs.-temperature curve in the datasheet.
UPDATE 7/5/2001 - Lumileds datasheets for their "lambertian"/"high dome" red Luxeons indicate that they produce 30.6 lumens minimum, 44 lumens typical at 350 mA with a 2.95 volt typical voltage drop. This is 29.6 lumens/watt minimum (assuming the typical voltage drop), 42.6 lumens/watt typical. I expect overall luminous efficacy to be even a little higher at somewhat lower currents around 200 mA. This model uses those truncated inverted pyramid dice mentioned above.
The "Low Dome"/"Batwing" is not as efficient and produces less light. The high dome but not the low dome ones use truncated inverted pyramid dice.
UPDATE 1/26/2009 - TT Electronics / Optek Technology now makes similarly efficient red LEDs typically producing 45 lumens from 350 mA with a typical voltage drop of 2.3 volts, when junction temperature is 25 degrees C, according to their datasheets. This works out to 55.9 lumens/watt. My interpretation of the datasheet is to expect usually at least 10% less with realistic heatsinking. Part numbers include OVTL01LGAR and OVTL01LGARS, both of which are available at Digi-Key.
UPDATE 1/26/2009 - Cree has their XRCRED-L1-R250-00M01, available at Digi-Key. According to the datasheet, these typically produce 39.8 lumens at 350 mA with a typical voltage drop of 2.2 volts. This works out to 51.7 lumens/watt. This is when junction temperature iis 25 degrees C. I would expect 10-15% less with realistic heatsinking.
UPDATE 7/5/2001 - The Lumileds datasheets for their "lambertian"/"high dome" red-orange Luxeons indicate that they produce 39.8 lumens minimum, 55 lumens typical at 350 mA with a 2.95 volt typical voltage drop. This is 38.5 lumens/watt minimum (assuming the typical voltage drop), 53 (corrected 5/25/2003) lumens/watt typical. I expect overall luminous efficacy to be even a little higher at somewhat lower currents around 200 mA. These use those truncated inverted pyramid dice mentioned above.
As for low power ones:
UPDATE 10/31/2009: Nichia NSPRR70AS, version with nominally 615 nm dominant wavelength (NSPRR70AS is nominally red): Dominant wavelength of 615 nm has a color that sometimes appears orangish red and usually appears reddish orange. At 50 mA, typical voltage drop is supposed to be 2.4 volts and typical light output is supposed to be 9 lumens. This works out to 75 lumens/watt.
UPDATE 10/12/2009: Osram LA E65F-CBEA-24-1-Z, in stock at Digi-Key, typically achieves 66.7 lumens/watt according to its datasheet. The datasheet states that typical performance at 50 mA is 7.17 lumens and a typical forward voltage drop of 2.15 volts.
Avago has the HLMP-DJ** LEDs, which are truly orange. The dominant wavelength is supposedly 605 nm, which is about that of an NE-2H neon lamp, and less red than the color of most other orange LEDs. The HLMP-DJ08 supposedly has a 9.5 candela 6 degree main beam.
UPDATE 5/27/2000 - HLMP-DJ24, 18-21 lumens/watt! The color was extremely slightly more red than that of an NE-2H neon lamp and much less red than that of other orange LEDs. The HLMP-DJ24 is a 23 degree model with a typical beam intensity of 2 candela.
Also note that these brightest HLMP-D*** part numbers are obsoleted and the current ones have HLMP-E*** part numbers.
UPDATE 7/13/2009 - Nichia NS6A083B is an amber-yellow LED whose datasheet shows a spectrum indicating that it is a phosphored LED. It typically produces 55 lumens at 300 mA with a typical voltage drop of 3.3 volts, working out to typically 55 lumens/watt.
UPDATE 1/2/2007 and 7/13/2009 - White LEDs can be filtered to yellow with yellow filters or "lenses". Typically 60-75% of the luminous/photometric output of a white LED gets through as reasonably yellow light. 40-70 lumens/watt (100 lumens/watt as of mid 2009) is possible by filtering the most efficient white LEDs. The downside is that white LEDs usually have worse aging characteristics than yellow LEDs.
The loss is greater if filtering to an orangish or "amber" shade of yellow suitable for traffic signals.
UPDATE 7/5/2001 - Lumileds datasheets for their "lambertian"/"high dome" amber Luxeons indicate that they produce 23.5 lumens minimum, 36 lumens typical at 350 mA with a 2.95 volt typical voltage drop. This is 22.7 lumens/watt minimum (assuming the typical voltage drop), 34.8 lumens/watt typical. I expect overall luminous efficacy to be even a little higher at somewhat lower currents around 200 mA. This model uses those truncated inverted pyramid dice mentioned above.
As for low power yellow LEDs:
UPDATE 10/12/2009 - Osram LY E65F-CADA-46-1-Z, in stock at Digi-Key, typically achieves 44.6 lumens/watt according to its datasheet. Typical performance at 50 mA is output of 4.8 lumens and forward voltage drop of 2.15 volts.
As for low power yellow LEDs in my testing: UPDATE 4/3/2010 Cree C503B-ABN-CW0Z0251, one sample tested so far, produces 1.36 lumens at 20 mA with a voltage drop of 1.99 volts, meaning 34 lumens per watt. Digikey has these LEDs. Their website says 2.5 lumens, but I suspect they botched an oversimplified formula and meant to say .63 lumen based on 5 candela and 23 degree beam angle, by using 23 degrees as half-angle.
I do expect that Osram, Toshiba, Avago and others have fair chance of achieving similar luminous efficacy with low power non-phosphor yellow / amber LEDs.
Some Toshiba LEDs and AND ones that look like Toshibas have an overall luminous efficacy around 3-4 lumens per watt. These are very yellowish green LEDs with a dominant wavelength around 570-573 nm:
Toshiba TLGA183P, Hosfelt Electronics catalog number of 25-341, US$ .99 according to their 99-B catalog, beam approx. 7-8 degrees, claimed brightness 3 candela.
AND's AND183HGP, Newark Electronics catalog number 92f2644.
Toshiba TLGE185EP, Hosfelt Electronics 25-366 has a better defined beam of supposedly 3.5 candela (I think 2-2.5) and maybe about 15 degrees but no higher efficiency. $.99 from Hosfelt according to their 2003 catalog.
LEDs of similar color but with overall luminous efficacy similar to, maybe slightly higher than that of white ones can be made by suitably adding a suitable fluorescent dye to white or blue ones. That means about 40-80 lumens/watt! If you put a white or blue LED into a piece of green-fluorescing yellow acrylic this will probably work! Go Here for LED Hacking for Fun and Danger.
UPDATE 11/2/2004 - Cree XL7090 green "XLamps" typically produce 34 lumens at 350 mA with a typical voltage drop (according to the XB900 chip datasheet) of 3.4 volts. This works out to 28.6 lumens/watt. Other green LEDs with Cree chips have already achieved 33 lumens/watt in my tests.
Now for "low power" green LEDs:
UPDATE 4/28/2009 Cree CP41B-GFS-CM0N0674 and CP41B-GFS-CM0N0784 are 4-lead "high flux" / "spider" / "piranha" LED lamps available from Digi-Key. The Digi-Key website says that at 30 mA, typical luminous flux is 8.05 lumens and typical voltage drop is 3.6 volts. This works out to 74.5 lumens/watt.
The datasheet for these says that the minimum luminous flux is 5.5 and 8.73 lumens respectively. Assuming 3.6 volt voltage drop, this works out to 50.9 - 80.8 lumens/watt. With 6.6 lumens as borderline between the two brightness ranks covered, lumens/watt is 61.1. Using 7.59 lumens as center of top rank on a log scale, lumens/watt is 70.3. These luminous efficacy figures will vary inversely with voltage drop.
The -674 unit has dominant wavelength 515 to 525 nm, and the -784 unit has dominant wavelength 520-530 nm.
UPDATE 1/1/2008 - I tested several units of Nichia NSPG510AS, NSPG520AS and NSPGF50AS. My tests indicate at 20 mA average forward voltage drop of 3.05 volts and light output ranging from 3.7 to 4.4 lumens. The datasheet says typical forward voltage drop is 3.2 volts. This indicates 58 to 72 lumens per watt overall luminous efficacy.
UPDATE 12/25/2007 - I just got a batch of NSPG510AS units that average 72 lumens/watt at 20 mA. At 3 mA, they had a forward voltage drop averaging 2.6 volts and produced on average .94 lumen according to my testing, for an overall luminous efficacy of 120 lumens/watt.
UPDATE 7/28/2009 - I tested a NSPG520AS at 1.69 milliamps, and found forward voltage drop of 2.45 volts and quantum efficiency of 29.5%. The color matched that of a Nichia green LED whose spectrum was analyzed with results indicating average photon energy of 2.339 eV and luminous efficacy of the emitted light being 512 lumens/watt. This indicates conversion efficiency of 28% and overall luminous efficacy being about 140 lumens/watt.
My experience is that other InGaN green and blue LEDs have a similar increase in luminous efficiency, and that white ones have a lesser but significant increase in luminous efficacy when underpowered. However, if current is reduced to less than 5% or so of typical current, then efficiency may decrease.
Now for "low power" LEDs:
UPDATE 7/30/2000 - TESTED BG MIcro LED-1052 narrowbeam bluish green Nichia NSPE590S - preliminary figure 24-26 lumens/watt on the single sample ordered. This model has an irregular beam with a small central bright pattern (roughly 7 by 4 degrees) with a claimed typical brightness of 20,800 mcd at 20 mA.
TESTED Hosfelt Electronics 25-376, apparently a Nichia model. Tentative figure for overall luminous efficacy 24-27 lumens/watt. Optical power output 7 mW at 20 ma with a 3.75 volt voltage drop - 9.3 percent conversion efficiency! Expect even better efficiency in the future since the voltage drop will usually be 3.3-3.6 volts.
Cree and Avago also make bluish green LEDs suitable for traffic signals.
UPDATE 7/17/2007 - Cree XRE blue LEDs in their flux rank of J0 produce minimum 23.5 maximum 42 lumens at 350 mA with a voltage drop of typically 3.3 maximum 3.9 volts. This works out to minimum 17.2, highside 30.7 lumens per watt at 25 C junction temperature.
Now for "low power" blue LEDs:
UPDATE 1/3/2008 - UNTESTED, SIGHT UNSEEN: Nichia has new blue LEDs recently becoming available. They mostly have a revision letter 1 beyond that of their long-standing blue ones. An example is NSPB500AS, which is the improvement of NSPB500S and is claimed to have a beam intensity of 11 candela at 20 mA.
According to published millicandela figures and my extrapolation from my testing of related white Nichia LEDs, it appears to me that output is roughly tripled. With a voltage drop of typically 3.2 volts instead of 3.5 volts, efficiency is increased by a factor of *very roughly* 3.3 (and this is an extrapolation of mine, not an actual test result). With NSPB500S achieving probably about 8 lumens per watt, I expect the new models to achieve about 25 lumens per watt. I expect optical output at 20 mA to be about 22 mW, for a conversion efficiency around 34 percent.
UPDATE 5/11/2009: Digi-Key has in stock Cree CP41B-BFS-CG0H0454, which is mentioned by Digi-Key to produce typically 3.13 lumens at 30 mA with a voltage drop of typically 3.6 volts. This works out to 29 lumens/watt.
Also consider that Cree, unlike Nichia, produces reliably available quantities of LEDs with the 460 nm deeper blue wavelength in addition to the usual 470 nm wavelength. 460 is better than 470 for use in LED video displays - 460 nm has greater "blue color impact" useful in an RGB device than 470 nm despite 460 nm having lower photometric performance than 470 nm. Photometric output of an RGB device is normally almost entirely from stimulating green and red receptors in the human eye rather than blue, so blue LEDs with greater "blue impact" and purer shade of blue and producing more radiometric output can easily have inferior photometric specifications despite their superiority. One thing to look for is photometric output after multiplying by the ratio of Z to Y CIE chromaticity figures.
This is with junction temperature of 25 degrees C, as opposed to heatsinkable surface being at 25 degrees C. However, with 6 degree C per watt thermal resistance, typical luminous efficacy at 350 mA should be close to the same, around 123 lumens/watt.
Digi-Key incorrectly mentions both 130 lumens and test current of 1.0 amp. This LED's maximum current is 1.0 amp, at which it produces about 2.48 times as much light as it does at 350 mA (or about 320 lumens, if cooled sufficiently to maintain junction temperature of 25 degrees C.)
(At 1 amp with heatsinkable surface temperature of 25 degrees C, I work out junction temperature of 45 degrees C and 4.4-5% less light, or about 305 lumens.)
The datasheet for Cree XP-G LEDs is here.
UPDATE 5/11/2008 - Philips-Lumileds "Luxeon Rebel ES" has rated minimum luminous efficacy of 100 lumens/watt at 350 mA with a test method that I like to see as reporting results with junction temperature of 25 degrees C and with measurement tolerance of +/- 8.5%, according to the Philips-Lumileds "DS61" datasheet on Luxeon Rebel ES.
The Philips-Lumileds part numbers are LXLW-PWC1-0100 ("cool white", with typical color temp. 5650 K) and LXLW-PWN1-0100 ("neutral white", with typical color temp. 4100 K).
Operated continuously rather than with brief pulse at thermal pad temperature of 25 degrees C, so that junction temperature at 350 mA is typically 35.5 degrees C (3.0 volts typical voltage drop, 10 degree C per watt thermal resistance), I see the curve on page 12 of the DS61 datasheet indicating decrease of about 1.5%. Combined with +/- 8.5% tolerance in their photometric measurements, I like to see minimum of 90 lumens/watt when temperature of the heatsinkable surface is 25 degrees C.
I would reduce that to minimum (including the 8.5% going downward) of 88 lumens/watt when the "thermal pad" (heatsinkable surface) temperature is cooled to a very-well-cooled-side-of-"real-world" 35-40 degrees C.
I would like to add that 88 lumens/watt minimum in "real-world-achievable" conditions is very significant. And that is for "neutral white" - the "DS61" datasheet makes it appear to me that this 90 lumens/watt for "cool white".
UPDATE 4/30/2010 - Nichia NCSW119 with 350 mA current typically produces 130 lumens with a typical voltage drop of 3.3 volts. This works out to typically 112.5 lumens/watt. This LED is a version with a less-bluish but still "cool" shade of white, with a claimed typical chromaticity that is close to that of 5,000 Kelvin.
UPDATE 8/10/2009 Luminus CST-90-W at 3.2 amps and SST-50-W at 1.75 amps have borderline between the top two brightness ranks being 1000 and 550 lumens respectively, with typical voltage drop of 3.2 volts. These both work out to 98 lumens/watt.
UPDATE 1/3/2008 - Seoul Semiconductor "P4" W42180U, W42182U, (top brightness rank of "U"), available from Mouser Electronics, using dice/"chips" by Cree: 91 lumens minimum, 100 lumens typical at 350 mA at heatsinkable surface temperature of 25 degrees C, and voltage drop of typically 3.25 volts, maximum 3.8 volts. This works out to 68.4 lumens/watt minimum, 87.9 lumens/watt typical.
These LEDs have absolute maximum current of 1 amp. Light output at 1 amp is typically 2.4 times that at 350 mA according to a graph in the datasheet. Typical forward voltage drop at 1 amp is about 3.6 volts according to a graph in the datasheet. This is at heatsinkable surface temperature of 25 degrees C according to the datasheet. This means supposedly 218 lumens low side 240 lumens typical at 1 amp, with luminous efficiency 60.5 lowish side to typically 66.6 lumens per watt at 1 amp and heatsinkable surface temperature of 25 degrees C.
NOTE - All high power white LED data above is from datasheets and datasheet interpretations and not personally experienced actual test results.
I have actually tested these Soul Semiconductor upper rank P4 LEDs and on a *preliminary basis* got about 90 lumens at 350 mA. Due to tolerances of my testing methods done so far, I cannot say with any confidence that they were as indicated actually close to barely minimum specified performance, and they could easily have done better.
UPDATE 5/11/2009Cecol / Citizen Electronics produces their CL-L233-C13N with nominal light output of 1335 lumens at 720 milliamps with a typical voltage drop of 18.6 volts, which works out to 100 lumens/watt.
UPDATE 1/26/2009 - Citizen Electronics AKA "Cecol" has an 8-chip white LED lamp (CL-654-C1N) rated to typically produce 96 lumens from 1.21 watts. That works out to 79.5 lumens/watt. My tests on samples that I have obtained indicate about 92-plus lumens from 1.21 watts (76-plus lumens/watt).
Nichia's most efficient high power white LEDs in their website as of 5/11/2009 are:
NS9W153M, typical performance 350 lumens at 350 mA with voltage drop of 10.5 volts, which works out to 95 lumens/watt.
NCSW136, typical performance 190 lumens at 550 mA with voltage drop of 3.5 volts, which works out to 99 lumens/watt.
Now for "low power" white LEDs:
UPDATE 4/10/2010 - Nichia has a 5 mm white LED lamp, NSPW500DS, that is similar to NSPW500S except with higher output and a nominally narrower beam - and a beam intensity of typically 27 cendela at 20 mA. Preliminary testing of related units with "D" revision letter (NSPW510DS) indicate 55-65 lumens/watt. I just tested a 2008-vintage NSPW510DS and found it to achieve 68 lumens/watt (conservatively), but which may be a little on the high side for that vintage to be determined "so conservatively".
Update 5/11/2009: Nichia has an extremely efficient 4-lead LED, NSPWR70CSS-K1, A.K.A. NSPWR70CS-K1. At 20 mA, it is said to typically produce 8.7 lumens at 20 mA with a typical voltage drop of 2.9 volts, which works out to 150 lumens per watt. At 50 mA, typical luminous flux is stated to be 20 lumens and typical voltage drop is stated to be 3.1 volts, which works out to 129 lumens/watt.
I have tested this LED. My testing indicates 140-145 lumens/watt at 20 mA for a few that I have tested.
UPDATE 4/10/2010: As for a 2-lead through-hole "5 mm" non-Nichia DigiKey- available LED, there is the Cree C535A-WJN-CU0V0231. My composite result from 2 different testing methods is 81 lumens/watt at 20 mA, 97 lumens/watt at 8 mA, and peaking at 102 lumens/watt at 2.2-3 mA.
This LED appears to me to be one where the light-emitting surface is a convex surface that most rays of outgoing light are largely close to perpendicular to both before and after exiting the forward surface of the LED. It appears to me that this reduces internal reflection losses, but also results wider beam angles. This LED has a nominal beam width of 110 degrees.
The above white LED lamps have blue chips plus a phosphor to convert some of the blue light to yellow light of broadband spectral content from mid-green to mid-red. The color is usually a cool white to "daylight" slightly bluish or sometimes violetish-bluish white, usually of about 5000-6500 K. Color rendering index of the most efficient ones as well as most other white LEDs is stated to be 65 or 70 when stated. There are white LEDs with improved color rendering index, but their overall luminous efficacy is compromised.
Efficiency continues to increase with decreasing current at least down to 4 mA and is close to peak around 2-3 mA and remains above the 20 mA efficiency usually at least down to .5-1 mA. Efficiency and light output become less predictable below .4-.5 mA.
White LEDs have most of their photometric output from a phosphor, and so the luminous efficacy of emitted light does not improve with decreasing current as much as with colored InGaN LEDs. In fact, spectral shifting of the LED chip's output away from wavelengths best-utilized by the phosphor can impair overall luminous efficacy at low currents. However, photometric output per milliamp seems to usually improve with decreasing current down to about 6 milliamps, sometimes as low as 3 milliamps. I have tested one low power white LED (Cree C535A-WJN-CU0V0231) at various currents, and found ratio of photometric output to current to be maximized at 4-5 mA, achieving about 1.135 times that achieved at 20 mA. This LED had efficiency maximized at 2.2-3 mA, with efficiency about 1.26 times that at 20 mA.
Important Note on Gallium-Nitride LEDs!
Gallium nitride and indium gallium nitride LEDs are fussy, and do not
like their ratings to be exceeded. Exceeding 5 volts reverse voltage even with
low current is supposedly damaging to them. I suspect that destructive
electrolysis is what goes wrong. Peak forward currents in excess of 100 mA
may also be bad. These LEDs are also supposed to be considered static sensitive.
These are the first well known keychain LED flashlights and may still be the brightest. Available in all colors.
Brightest white 5 mm LED lamp that I am aware of as of 5/11/2009: Nichia NSPW500DS (15 degree beamwidth, 27 candela) and Nichia NSPW500GS-K1 (same beam angle, 30 candela, but has compromised life expectancy).
UPDATE 8/8/2009: Luminus CSM-360-W is a very high power LED with 4 large dice (chips) in series and a maximum current of 6.3 amps. Luminous flux (output), depending on bin/rank, is in the ballpark of 3,000 lumens at 3.2 amps, with a typical voltage drop of 12.8 volts, working out to 41 watts and 73 lumens per watt. Output and efficiency are 20% greater at the borderline between the highest two binning ranks.
Opto Technology makes 40-chip TO-66 lamps that can take 8-10 watts.
Norlux makes 40-chip heatsinkable lamps.
Lumileds, a joint venture of Agilent and Philips Lighting, makes high power heatsinkable "Luxeon" LEDs, in wattages as high as 5 watts, some of which produce over 200 lumens.
Cree and Nichia are getting into this game with ~1-1.2-2-3 watt LED lamps.
Nichia has a link here.
Osram has their "Golden Dragon" and multichip "Ostar" high power LEDs.
Lamina Ceramics produces heatsinkable high power LED arrays. Some of their arrays take over 100 watts and are of size 1.06 by 1.25 inches (31.75 by 26.67 mm) - and this obviously needs major heat sinking. Please consider thermal resistance of the device and light output as a function of junction (LED "die" or "chip") temperature!
Cecol / Citizen Electronics produces an LED with nominal light output of 1335 lumens at 720 milliamps with a typical voltage drop 0f 18.6 volts (100 lumens/watt).
LEDEngin is a maker of 1-chip high power LEDs and 4-chip ones with nominal wattage as high as 15 watts.
Some Avago, Chicago Miniature, and most AND (apparently Toshiba) LEDs are available from Newark Electronics. Call 800-4NEWARK or visit http:/www.newark.com. They are in a position to collect sales tax if you live in or order from any U.S. state with a sales tax. Minimum order is US$ 25. In addition, the minimum order for most Chicago Miniature Lamp items is 10 pieces of each type. Shipping is extra and duplicate shipping charges apply if you order more than one type of item not all in stock in the same warehouse. Higher minimums may apply to non-stock merchandise - often 500-1000 pieces of any non-stocked Avago LED lamp and maybe even for some stocked ones, and this applies with some other Avago distributors as well.
Future Electronics is the main distributor of Lumileds products and is a distributor of other LEDs.
Hosfelt Electronics sells some bright Toshiba LEDs and some other interesting LEDs.
Phone: 800-524-6464, 888-264-6464, 614-264-6464
FAX: 800-524-5414, 614-264-5414
Web: http://www.hosfelt.com/index2.htm
or http://www.hosfelt.com
Orders shipped to Ohio addresses subject to 6.5 percent sales tax. No minimum
order for prepay or credit card orders, shipping is extra. Prepay orders must
include $6.50 for shipping, any excess will be refunded. Some items mentioned
on this web page may be out of stock or discontinued - check with Hosfelt,
not me for stocking status.
Hosfelt has some typo errors - some blue LEDs have lowish supposed voltage drop figures like 2.6-3 volts, but expect about 3.5 volts at 20 mA. Some strange beam angle figures have appeared in their web site and some of their catalogs - 29.5 and 28.5 degrees. Possibly someone saw the "two-theta-half" symbol which resembles 28 1/2 as the actual number of degrees. These look like typos, maybe on the part of a datasheet from a supplier, and are not attempts on Hosfelt's part to give falsely optimistic specifications.
Nichia LEDs are best obtained from their sales offices. In North America, check out Nichia America.
Toyoda Gosei makes bright green and blue LEDs.
Toyoda Gosei LED info is now on the web at http://www.toyoda-gosei.co.jp/led/e-index.html.
Michael W. Sforza's Custom Model Light Service (e-mail lightforce1@rcn.com) also sells bright LEDs. Stock is limited, selection is limited but growing, and prices seem reasonable. E-mail for prices and inquiries. This business specializes in sales of smaller to medium quantities of LEDs and customized addition of lights to building, railroad, vehicle and other models.
A lumen is defined as the "luminous flux" of 1/683 of a watt of monochromatic
light that has a frequency of 540 terahertz, or a wavelength of approx. 555.5
nm.
One thing worth noting is that a lumen is defined secondarily, in terms of
the candela (which is 1 lumen per steradian), and the candela is defined
primarily (it's the "beam candlepower" of 1/683 watt per steradian of 540 THz
monochromatic light.)
Light of wavelengths other than 555.5 nm have a different amount of lumens
per watt of radiation. The number of lumens in a watt of wavelength other
than 555.5 nm is 683 times the photopic function of
the wavelength in question, divided by the photopic function of 555.5 nm
(which I believe is very close to but not exactly 1).
A "USA-usual" 100 watt, 120 volt, 750 hour "regular" (A19) lightbulb usually produces 1710 lumens.
Lumens per watt is a measure of efficiency in converting electrical energy to light. Multiply this by the watts dissipated in the LED to get lumens. A typical red, orange, or yellow or yellow-green LED has a voltage drop around 2 volts and is getting around .04 watt at the typical "standard" current of 20 milliamps. A blue, white, or non-yellowish-green one typically has a voltage drop of 3.5 volts at 20 mA and gets .07 watt at 20 mA.
A candela is a lumen per steradian, or "beam candlepower". (Actualy, as
mentioned above, the candela is a primarily defined metric unit, while the
lumen is defined in terms of the candela.)
So lumens are candelas times the beam coverage in steradians. Candelas are
lumens divided by the beam coverage in steradians. Ideally, that is -
assuming that all light is within the beam and the "candlepower" is
constant within this beam.
So you may now be wondering what a steradian is. It is 1 / (4 * pi) of a whole sphere or 1 / (2 * pi) of a hemisphere or about 3283 "square degrees", to the extent there is such a thing as a "square degree". To get steradians from the beam angle:
Steradians = 2 * pi * (1 - cos (.5 * (beam angle)))
(NOTE: There are a few other expressions equal to this. Proving that is homework for 12th graders taking trig / "elementary functions".)
So if you determine the steradian beam coverage and multiply that by the candela figure (or 1/1000 of the millicandela figure), you get the lumen light output - very roughly! The beam is not uniform and it does not contain all of the light. Obtaining lumens from beam angle and candela can easily be in the +100 / - 50 percent range. Actual lumens are generally higher than predicted by this formula with smaller beam angles of 8 degrees or less since the nominal beam does not include a secondary "ring-shaped" "beam" that usually surrounds the main one. Also note that some beam angle figures are optimistic and could lead one to expect a lot more lumen light output than actually occurs.
Please read my disclaimer.