Testing IR LEDs

[DrG]

Maybe almost everyone already knows this, but maybe a few new enthusiasts do not.

I was testing some IR LEDs the other day and used my digital camera to "see" whether they were working. To the normal naked eye, of course, one can't tell the difference.

Not working:

Working:

 

[ronsimpson]

used my digital camera to "see"

Cameras come in many different types. Some have IR filters to block IR.
Some cameras have Red, Green, Blue & IR sensors. four types of sensors.
There will be different effects depending on what camera you use.
Good idea to use a camera!

 

[alec_t]

A 'converse' of the effect shown is that the camera would 'see' a white LED and an IR LED as similar, whereas the human eye wouldn't.

 

[DrG]

Cameras come in many different types. Some have IR filters to block IR.
Some cameras have Red, Green, Blue & IR sensors. four types of sensors.
There will be different effects depending on what camera you use.
Good idea to use a camera!

I don't doubt what you are saying. The digital cameras that I tested (Canon P&S, Old Digital Rebel, SL2, smartphone) all can be used - at least to discriminate on/off. I do have a couple more digital cameras that I could test. I would have to wonder about this one, which I bought for US$8 on sale back in 2008):

That does not mean, however, that all digital cameras will work. I wonder...does anyone have a digital camera that will not work this way?

The other thing I would be interested in testing using an IR LED is how well commercial IR filters work. I don't have one though. Edit to add - those filters are designed to block visible light, not IR. You should still "see" a nice difference with the IR LED pic in "normal" lighting.

 

[DrG]

A 'converse' of the effect shown is that the camera would 'see' a white LED and an IR LED as similar, whereas the human eye wouldn't.

With regard to the few different cameras that I tested, the hue of the IR was different - light blue to violet.

 

[ronsimpson]

I have some cameras with "day/night" options. In "day" mode it just sees the IR LED. In "night" mode the LED lights up the room.

 

[DrG]

I Lied!! My SL2 does not pick up the lit IR LED! Tried a couple of lenses. I wonder if I was thinking about the old digital rebel - hmm dunno.

The LG smartphone does:

The Point@shoot (powershot) picks it up very well.

Those are all the same IR LED with a 330 resistor @ 5V

Humph!

 

[DrG]

I have some cameras with "day/night" options. In "day" mode it just sees the IR LED. In "night" mode the LED lights up the room.

Well that sounds like an IR filter that blocks visible light...and it is on a switch or menu function? What camera is that may I ask? [and *dam* you, now I have to look at what the "night" scene setting does!

Edit: well don't dat just beat all!

In night scene it picks up the IR. Cool. Of course, I have never used any of those auto scenes. In fact, there is so much on this camera that even though I have had it for a good 4 months, I am not sure I have even touched the surface.

It's interesting, it doesn't want to auto-focus my EFS 60mm lens, which may make sense if it is blocking visible light...it has nothing to focus on...it also does multiple shots for HDR. Cool stuff, thanks for bringing it up (I un-dam you ).

 

[Pommie]

I had a video camera with night mode. It used IR LEDs to illuminate the scene. Many video cameras from the 90s had this function.

Mike.

 

[gophert]

Or, you can grab a second IR LED and connect the anode to 5V and the cathode to a 33k to 100k resistor. Connect the other resistor to ground. Then measure the voltage across the resistor. It should be zero volts. Then shine your test IR LED on it and the voltage should bounce 1 to 3 volts. A larger resistance will vice you more noise in the off state but also a higher voltage when IR is hitting it.

 

[ronsimpson]

Again, every camera is different.
In a camera all the sensors are the same but they have different filters. From this picture some sensors have a blue filter, or green filter, or a red filter. In this case there is a IR blocking filter because "hot objects" should not look different to the camera than to your eye. (yellow line is the visible light filter or IR block filter)

I have used CMOS & CCD cameras. As you can see they respond well to IR light.

I have some cameras with 4 not 3 sensors/pixel. In day mode they use the R, G, and B sensors. In night mode they use the 4th sensor with no filter. The 4th sensor pulls in much more visible light and responds very well if there is a IR source.

There are some cameras, to save money, that do not have a IR blocking filter. In night mode they just use the red sensors that extend out to 1000nM. (wave lenght)

 

[DrG]

BTW: Back in post #8, I said:

It's interesting, it doesn't want to auto-focus my EFS 60mm lens, which may make sense if it is blocking visible light...it has nothing to focus on...i

This is nonsense - it amazes me sometimes when I will come up with an explanation that makes no sense, if I just think about it for a minute. The reason that the auto-focus was not working was because the contacts needed cleaning and it had nothing to do with anything else.

This fixed the problem.