Light filter around 592 nm
Light filter around 592 nm
(OP)
Hi, we currently have a wide range of LEDs (582 to 602 nm) we need to keep only the ones around 592 nm ±1 nm. This is very hard to see the difference by eye (selection will be made in china so worktime is not an issue). So what I tough was that we should order a light filter that will only let pass the right wavelenght.
Lens should be 10cm x 10cm.
Am I aiming in the right direction ? Or should I use another method?
Thanks
BeerBaron
Lens should be 10cm x 10cm.
Am I aiming in the right direction ? Or should I use another method?
Thanks
BeerBaron





RE: Light filter around 592 nm
Moreover, given the wide range you've specified, it would seem to be a very expensive cherry-pick.
TTFN
RE: Light filter around 592 nm
So what range would be a cheaper filter technique?
BeerBaron
RE: Light filter around 592 nm
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While is possibly reasonable, cost-wise for the filter, the overall concept still seems problematic. Your products have an overall range of 20 nm, for which you're screening for even 3nm, is 1/7 of the total product, assuming uniform distribution. What are you going to do with the 86% rejected parts?
Why do you need such a tight wavelength for LEDs?
TTFN
RE: Light filter around 592 nm
We woudln't lose 87% of our LEDs since it's probably more a gaussian distribution. We buy the LEDs from a manufacturer that claims 592 ±.5 nm but it's far from the truth since I can find 2-5% of completely different ones.
We are willing to throw away 5% of our LEDs without too much problems.
Regards
Frederic Boucher
RE: Light filter around 592 nm
Not sure what your operating temperature is, but a 20 degree downward shift would shift the wavelength well below your acceptance criterion.
TTFN
RE: Light filter around 592 nm
Moreover, unless you run a filter/no filter comparison, you can't be sure why an LED fails OR passes.
Overall, I'm unclear why you have an upper limit. Presumably, 602 nm should be a perfectly acceptable red.
I'm not even clear why 592 is necessarily bad. Aren't your LED potted in red plastic to begin with? Again, I would suggest that you get LEDs that have a distribution farther into the red, just to avoid this whole exercise.
TTFN
RE: Light filter around 592 nm
LEDs would be processed with a breadbord, 100 at a time (15 minuntes to load a breadboard). It's being done in a factory in China so it would be more like 0.001$ per LED from a workforce point of view.
Regards
Frederic Boucher
RE: Light filter around 592 nm
You should realize that the interference filter test may be difficult to pull off with untrained labor. The center wavelength of interference filters varies like cos(theta), where theta is the zenith angle of incidence. You get a 1-nm shift for 3.3 degree misalignment and 3-nm shift for 5.8 degree misalignment.
Because of this, the geometry and spatial extent of your proposed breadboard may be a critical factor.
Curtis
RE: Light filter around 592 nm
As another alternative, I would suggest a machine vision camera with some software to electronicaly look at ratio between the red and green channels. This could potentially make it fully automated and remove the subjective decision making required from the operator.
TTFN
RE: Light filter around 592 nm
Curtis, I never tought of that problem but it is a real one if I go with a filter. I would need to make some kind of strict breadboard.
TTFN, both idea are good. A machine vision would be better implemented at the LED manufacturer since it could represent big investments.
Is a lowpass frequency filter potentially easier to make ?
Best regards
BeerBaron
RE: Light filter around 592 nm
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probably OG590
TTFN
RE: Light filter around 592 nm
BeerBaron
RE: Light filter around 592 nm
TTFN
RE: Light filter around 592 nm
I'd try to set up the system so the LEDs are delivered to the inspection station on tape and reel, inspected while still in the tape, then rolled up and sent on to the assembly station, with the bad LEDs missing from the tape.
I.e., inspecting them one at a time, quicker test duration, no manual handling, better net throughput. I wonder if someone already makes and sells such equipment, or something adaptable to do this job?
Mike Halloran
Pembroke Pines, FL, USA
RE: Light filter around 592 nm
TTFN
RE: Light filter around 592 nm
BeerBaron
RE: Light filter around 592 nm
While the camera/vision software approach requires some development, the approach would be substantially more robust and repeatable.
TTFN
RE: Light filter around 592 nm
Mike Halloran
Pembroke Pines, FL, USA