Really bright yellow LEDs?

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

 

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

 

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

 

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"?

 

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

 

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.

 

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

 

These 3W (found via mouser) claim (page 17) to have an Amber bin 1 as
low as 580-582.5, but it's not clear that you can easily order a single
bin (some hand-waving about 4 adjacent bins...)

http://www.everlight.com/datasheets/Shuen3W.pdf

Then there's 570/575 greens like this surface mount 75mW:

http://www.kingbrightusa.com/images/catalog/SPEC/AM2520CGCK09.pdf

 

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

 

If you don't know them already, Roithner have a wide range of leds (and
lasers).

 

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

 

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

 

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.

 

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

 

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

 

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.

?-)

 

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

 

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.

 

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

 

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.