A while back I purchased few LEDs, but can't recall what they exactly are .... IR/UV/else?
The plastic housing is 'clear', and when I hooked them up and powered them, 'nothing' happens.
I guess I could wire them up and take a video with a camera (cameras Do see IR), but was thinking: Is there a smarter/better way to find out what they exactly are?
jb63:
I guess I could wire them up and take a video with a camera (cameras Do see IR)
Apparently that's not foolproof; I read somewhere that later cameras filter that ability away.
Is there a smarter/better way to find out what they exactly are?
Put them in a labelled bag when you get them.
If they are UV then you should be able to get the 'black light' effect in a dark room with something white. I guess if they are not UV then they are IR.
Spectrometers can read the light and tell you the frequency. Here's one https://www.uprtek.com/en/category/Handheld-Spectrometer/CAT-Handheld-Spectrometer.html
marco_c:
Put them in a labelled bag when you get them.
Waaaay too simple 
hannah_mackinlay:
Apparently that's not foolproof; I read somewhere that later cameras filter that ability away.
While all cameras have an IR filter in them, these filters are not good enough to remove all the IR from an LED viewed close up.
I hope when you wire them up to your power supply you include a series resistor or they could just blow or at least be damaged depending on the nature of your power supply.
If you suspect that it is a IR LED, power it up in a dark room and set the camera in bulb mode and take long exposure. If it is a IR LED, it assume you will see a very red light (I have not tested it myself).
Also note that there are some cameras on the market with no IR filter, like the Canon 60Da. Perhaps you know someone that has one?
Or you could get a reasonable idea by measuring the forward voltage. IR LED will typically be <1.5V but UV LEDs will typically be >3V.
Steve
Grumpy_Mike:
While all cameras have an IR filter in them, these filters are not good enough to remove all the IR from an LED viewed close up.I hope when you wire them up to your power supply you include a series resistor or they could just blow or at least be damaged depending on the nature of your power supply.
I tried a proper camera, and my old and current mobile phones - the old mobile phone showed up IR much more
strongly, but all 3 could detect an IR led at 10mA. It looks purple, presumably an accident of the spectral responses of the RGB CCD cells.
UV LED's are easy to detect by eye since your cornea fluoresces nicely to give a purple halo to the thing, and
the spectral spread is quite broad. Point one at a fluorescent object and it will be very obvious!
The forward voltage of an LED is a huge clue though, 1.1V is IR, 1.6V red, 3V blue/violet, 3.5V UV, very
roughly.
If it is a IR LED, it assume you will see a very red light (I have not tested it myself).
Clearly you have not tested it yourself. The result is it looks cream on all the cameras I have tried.
Also note that there are some cameras on the market with no IR filter,
And they show up on that as a brighter cream. The cheapest is the Raspberry Pi Nir camera.
spectral responses of the RGB CCD cells.
Could be all the cameras I have used have had a silicon array sensor not a CCD, which is rare these days.
The cream colour results from all silicon sensors being sensitive to IR, more or less.
IR from daylight is very different spectrally from an IR LED at 940nm. IR from daylight is principally just off
the end of visible red at 750nm or so, well away from 940nm. The spectral response of the RGB dyes on
the sensor array are going to vary depending on the manufacturer I'd have thought, leading to different
apparent colours for various IR wavelengths and cameras.
I have an IR-pass filter for my big camera, you get pink/magenta images through it from daylight scenes. If you
convert those to monochrome greenery is a ghostly white colour as chlorophyll reflects IR strongly
(it absorbs both red and blue light)
Grumpy_Mike:
Could be all the cameras I have used have had a silicon array sensor not a CCD, which is rare these days.The cream colour results from all silicon sensors being sensitive to IR, more or less.
As far as I know CCD is just as sensitive to IR, also requiring IR filters to actually work. Some 20 years ago we could also see the IR from a remote control on digital cameras just fine. Must have been a CCD array back then. A great way to figure out whether your RC is actually still working.
It's always been white/cream colour. Never seen it show up as red. I am used to see IR LEDs as used in security cameras show up faintly red to the eye in the dark.
wvmarle:
... we could also see the IR from a remote control on digital cameras just fine ...
Thank you all, very useful responses. In fact, the above is what I was thinking, hopefully I still have an old CCD-based camera that can be used. Though now I have more options based on all the answers.
wvmarle:
It's always been white/cream colour. Never seen it show up as red. I am used to see IR LEDs as used in security cameras show up faintly red to the eye in the dark.
Interesting.
I have used trail cameras for several years to see the night time wild life around my property. I have often seen pictures of animals looking right at the camera. Taking video of coyotes at night, they will first glance up at the camera and then continue what they are doing.
It was a mystery, until one night, I was out and triggered the camera. I could see the red light from the IR LEDs when they first began to light up for the picture. Seems to be a programmed delay in the camera to wait till the red turns to IR, and then take the picture.
So, it seems the be a common feature of IR LEDs.
Paul
Paul_KD7HB:
Taking video of coyotes at night, they will first glance up at the camera and then continue what they are doing.
Now you mention it... indeed that's what I often see in wildlife documentaries. I never really thought anything of it, really.
I don't remember the red part to completely disappear. Many of those animals have anyway much better night vision than we do.
Here is a thought: How about we proceed by elimination?
The colored LEDs are rather obvious to identify, the LED color is simply the color of the plastic housing ... right?
What about housings that are Totally Clear? ... or, better yet, ...
How many different LEDs types/colors out there have CLEAR housing?
It seems to me only IR is the option. Right?
What's wrong with my reasoning?
- How many different LEDs types/colors out there have CLEAR housing?
It seems to me only IR is the option. Right?
I have LEDs in all colours that have in both clear and tinted housings.
The colored epoxy covering is to filter out ALL but the wanted color(wavelength).
Paul
The problem you have with tinted epoxy is that you have to see it blink before you know if it is in or off. With clear epoxy it is easier to see if an LED is on or off. I much prefer the clear ones.
jb63:
3. How many different LEDs types/colors out there have CLEAR housing?
Just thinking of my red LEDs in glass clear housing... and red/green two-wire bicolour LEDs in white milky housing... (those are also available in glass clear)
