Connect with us

Really bright yellow LEDs?

Discussion in 'Electronic Design' started by Phil Hobbs, Dec 14, 2013.

Scroll to continue with content
  1. Phil Hobbs

    Phil Hobbs Guest

    Hi, all,

    I'm building a multispectral sensor for food quality assurance for a
    large vendor. It has to work over a really large range of absorbance,
    at least 3 orders of magnitude. Red and green channels are not a huge
    problem, but the ones in between, like 570-580, are turning out to be
    much harder.

    The thing is, the primary-colour LEDs are roughly 50 to 200 times more
    efficient than the yellow ones I've found, so that I get at most 200
    microwatts of total output at 20 mA in the yellow, versus 8-10 mW from
    red, green, or blue ones.

    The best yellow-green one so far is the Avago HSME-A100, which still has
    a wall plug efficiency of less than 0.5%. I could really use 20 to 500
    mW from, say, 10 LEDs.

    Does anybody make high power LEDs in the 570 to 580 nm range?

    Thanks

    Phil Hobbs

    (To denizens of both SED and sci.optics: sorry for the mistyped cross-post!)
    --
    Dr Philip C D Hobbs
    Principal Consultant
    ElectroOptical Innovations LLC
    Optics, Electro-optics, Photonics, Analog Electronics

    160 North State Road #203
    Briarcliff Manor NY 10510

    hobbs at electrooptical dot net
    http://electrooptical.net
     
  2. Could you use an optical filter on a white LED? The yellow phosphor
    typically peaks around that range, though it's not a very sharp peak.

    http://www.cree.com/~/media/Files/C...dules/XLamp/Data and Binning/XLamp7090XRE.pdf


    Best regards,
    Spehro Pefhany
     
  3. Phil Hobbs

    Phil Hobbs Guest

    In the green (540 THz), 1 watt gets you 683 lumens. (Which is almost
    certainly the largest prime number ever used for unit conversion, and
    the absurd nomenclature of photometry is just getting going at that
    point. But I digress.)

    Assuming that the particular yellow hits the photopic curve at, say, 600
    lm/W, 750 millilumens would be 0.75/600 W, i.e. 1.25 mW. I'd really
    like 100 mW at 577 nm, but I could use as many as 10 LEDs to get there.

    Cheers

    Phil Hobbs


    --
    Dr Philip C D Hobbs
    Principal Consultant
    ElectroOptical Innovations LLC
    Optics, Electro-optics, Photonics, Analog Electronics

    160 North State Road #203
    Briarcliff Manor NY 10510

    hobbs at electrooptical dot net
    http://electrooptical.net
     
  4. Robert Baer

    Robert Baer Guest

    Probably not; what is surprising is that i understand that "white" is
    derived from "blue" and phosphor overlays, then "yellow" is another
    overlay on that.
    Maybe take the most efficient lower frequency blue and filter it for
    the yellow? Might be slightly better.
    Hell,one may even try red as some have strong blue bands.
    Use a DVD made by the pros for angle diffraction grating spectrum
    analyzer.
    Or...fuss with "orange"?
     
  5. Phil Hobbs

    Phil Hobbs Guest

    Interesting, thanks. I just need them to turn on and off at 20 kHz or
    so, so I'm not too worried about anything made out of direct bandgap
    semiconductors. It seems as though 575-580 is a lot harder to get than
    590-600, for reasons that I don't yet fully understand.

    Cheers

    Phil Hobbs


    --
    Dr Philip C D Hobbs
    Principal Consultant
    ElectroOptical Innovations LLC
    Optics, Electro-optics, Photonics, Analog Electronics

    160 North State Road #203
    Briarcliff Manor NY 10510

    hobbs at electrooptical dot net
    http://electrooptical.net
     
  6. High power LEDs only work for certain colors and that's not one of them.
    575nm LEDs, that I've seen, only exist as small decorative lamps. I
    have some in full color sample kit and they're the dimmest.


    Any chance you could create the right emissions from violet chips? The
    have WPE around 40% at intensities that are a fire hazard.
     
  7. Guest

    There are some part numbers dating from 2009 to 2012 listed at
    http://donklipstein.com/led.html#y . IIRC, Don used to post a lot on
    Usenet, and was amenable to "where do I get..." questions; it might be
    worthwhile to contact him directly.

    Matt Roberds
     
  8. Ecnerwal

    Ecnerwal Guest

  9. Phil Hobbs

    Phil Hobbs Guest

    Good suggestion, thanks.

    Cheers

    Phil Hobbs

    --
    Dr Philip C D Hobbs
    Principal Consultant
    ElectroOptical Innovations LLC
    Optics, Electro-optics, Photonics, Analog Electronics

    160 North State Road #203
    Briarcliff Manor NY 10510

    hobbs at electrooptical dot net
    http://electrooptical.net
     
  10. If you don't know them already, Roithner have a wide range of leds (and
    lasers).
     
  11. Phil Hobbs

    Phil Hobbs Guest

    Thanks. Those are actually the dimmish kind, like the Avago HLMP-Y802.

    At 578 nm, the photopic curve is still at about 90% of the peak, so we
    get about 600 lm/W optical.

    One candela is 1 lumen per steradian. The projected solid angle of a
    cone of half angle theta is

    Omega' = pi sin**2(theta).

    I need about 100 mW or more of optical power, which is about 60 lumens.
    I can use up to about 10 LEDs to get there.

    That means that I need the following minimum candela values (NOT
    millicandelas!):

    Projected
    Cone angle Solid angle Minimum
    (full) (sr) output

    10 deg 0.023 250 cd
    20 deg 0.095 63 cd
    30 deg 0.21 28 cd
    45 deg 0.46 13 cd
    60 deg 0.79 8 cd
    90 deg 1.57 4 cd
    120 deg 2.36 2.5 cd

    There's probably some specsmanship involved in the definition of the
    half-angle, but these will be reasonably close.

    Thanks

    Phil Hobbs
    --
    Dr Philip C D Hobbs
    Principal Consultant
    ElectroOptical Innovations LLC
    Optics, Electro-optics, Photonics, Analog Electronics

    160 North State Road #203
    Briarcliff Manor NY 10510

    hobbs at electrooptical dot net
    http://electrooptical.net
     
  12. Phil Hobbs

    Phil Hobbs Guest

    Thanks. I sent them an email earlier this week and haven't heard back
    yet. A 578-nm laser would be awesome, but it'd need to be at least 100 mW.

    Cheers

    Phil Hobbs

    --
    Dr Philip C D Hobbs
    Principal Consultant
    ElectroOptical Innovations LLC
    Optics, Electro-optics, Photonics, Analog Electronics

    160 North State Road #203
    Briarcliff Manor NY 10510

    hobbs at electrooptical dot net
    http://electrooptical.net
     
  13. High power LEDs only work for certain colors and that's not one of them.
    575nm LEDs, that I've seen, only exist as small decorative lamps. I
    have some in full color sample kit and they're the dimmest.


    Any chance you could create the right emissions from violet chips? They
    have WPE around 40% at intensities that are a fire hazard.
     
  14. Phil Hobbs

    Phil Hobbs Guest

    It looks as though the right answer is probably to use white LEDs and
    interference filters. With three or four detectors, the duty cycle goes
    up and the required bandwidth goes down, so I can get by with less
    light. The Luxeon LXS8-PW40 is pretty amazing: 1360 lumens from an 8-mm
    diameter device.

    With a 150-nm wide bandpass, I'll get something like 26 lumens in a 3-nm
    bandpass, but of course the efficiency will be lower, probably 50%. So
    two or three of those should be good enough.

    The main issue will probably be angle-tuning of the filters, which will
    limit the acceptance angle of the receiver. It would be nice to be able
    to use a single lens on the RX side, which means that the filters have
    to go on the photodiodes.

    An interesting question is what the optimal duty cycle should be for an
    on-off AC measurement--the "off" state should be stable for a long time,
    and with digital lock-in techniques, there's no particular reason to
    choose 50%. It seems as though the optimum should be near 100% if
    there's no systematic variation of the background, since one can average
    many "off" samples and get the noise in that state as low as one likes.

    Cheers

    Phil Hobbs

    --
    Dr Philip C D Hobbs
    Principal Consultant
    ElectroOptical Innovations LLC
    Optics, Electro-optics, Photonics, Analog Electronics

    160 North State Road #203
    Briarcliff Manor NY 10510

    hobbs at electrooptical dot net
    http://electrooptical.net
     
  15. Guest

    Kevin, where can I find these violet LEDs?
    Thanks.
     
  16. josephkk

    josephkk Guest

    Depends on how violet / ultraviolet you want. Both Cree and Nichia make
    them to less than 300 nm. Not terribly bright but at that wavelength they
    don't need to be, they get quite dangerous.

    ?-)
     
  17. There are ~watt up to ~1kW range output LED sources in the ~400nm
    wavelength range- one major application being UV polymerization.
    They're becoming practical in comparison to conventional mercury lamp
    sources. One supplier is Phoseon.

    Overall efficiency seems to be in the 20-25% range (measured from DC
    input). Water cooling is required for the high power sources.


    Best regards,
    Spehro Pefhany
     
  18. whit3rd

    whit3rd Guest

    If you modulate the LED light and use synchronous detection, you can just
    use more gain (without getting too badly clobbered by ambient light or noise).
    That's a cheaper way to go, when one considers (for instance) the unknowns
    like source aging/dimming.
    Just be glad you can GET the colors you want in LED form; I'd have been
    happy to pay kilobucks for a dim blue LED, thirty years ago. We used a
    mechanical chopper and HeNe-Cd blue laser instead.
     
  19. Phil Hobbs

    Phil Hobbs Guest

    I'm already doing that. The numbers I posted are what's required to get
    a SNR of about 60 dB in a 40-Hz bandwidth around a chopping frequency of
    a few of kilohertz. Some of the stuff I need to measure exhibits a path
    loss of 10**-8 (80 dB optical, 160 dB electrical). For a worst-case
    sample, half a watt of optical power will get me a signal photocurrent
    of 2 nanoamps, even with f/2 collection optics.
    I'm going to need an interference filter per channel anyway. He-cads
    weren't much fun to maintain, though their main output line at 442 nm is
    a beautiful colour. (I had one for awhile, many moons ago.)

    Cheers

    Phil Hobbs

    --
    Dr Philip C D Hobbs
    Principal Consultant
    ElectroOptical Innovations LLC
    Optics, Electro-optics, Photonics, Analog Electronics

    160 North State Road #203
    Briarcliff Manor NY 10510

    hobbs at electrooptical dot net
    http://electrooptical.net
     
  20. Kevin, where can I find these violet LEDs?
    Thanks.[/QUOTE]

    Ah, I didn't see this earlier because of my filter against Google spam
    flooding.


    Cree and Philips make some good ones.

    Philips LXML-PR02-1100
    1100 mW minimum @ 700 mA
    440 - 460 nm wavelength
    Vf 3.00 typical
    Case is 3.17 x 4.61 x 2.10 mm
    Lens is a silicone hemisphere on one side


    Philips LXZ1-PR01-0600
    600 mW typical @ 500mA
    440 - 460 nm wavelength
    Vf 2.90 typical
    Case is 1.30 x 1.70 x 0.66 mm
    Naked square emitter


    Cree has high power UV LEDs. I'd quote some Cree part numbers but their
    catalog is frustrating. Some of the Cree and Philips LEDs have similar
    enough dimensions that lenses are interchangeable.
     
Ask a Question
Want to reply to this thread or ask your own question?
You'll need to choose a username for the site, which only take a couple of moments (here). After that, you can post your question and our members will help you out.
Electronics Point Logo
Continue to site
Quote of the day

-