Re: TV remote control LEDs wavelength?

[Don Klipstein]

Does anyone know the approximate wavelength over which IR LEDs that
are used on TV remote controls operate?

These sure appear to me (in my experience) to be GaAs LEDs - usually
completely invisible in a dark room to most human eyes even when dark
adapted. I have seen some GaAs LEDs glowing barely in conditions
favorable for me to see them, but I usually find their output to be
completely invisible.

The peak wavelength of those is usually 940 nm.

There are GaAlAs infrared LEDs with peak wavelength usually 880 nm, at
least usually the nominal peak wavelength is. I usually find these to
slightly visibly glow when I look into them when they are operating.

I avoid staring into operating IR LEDs for more than a few seconds
unless I know that I am not going to exceed or get close to any limits of
21 CFR 1040.10, which actually does not have regulatory force over LEDs
anyway but on lasers. However, it does appear to me that TV remotes are
reasonably safe products.

- Don Klipstein ([email protected])

 

[JohnR66]

Does anyone know the approximate wavelength over which IR LEDs that
are used on TV remote controls operate?

[snip]

The peak wavelength of those is usually 940 nm.

Thanks Don. Now if you happen to have a digital camera, turn it on and
point the tv remote to the camera's lens. Push a button and then look
at the camera's digital screen. They are visible through the digital,
which means the digital responds to 940nm!

[snip]

- Don Klipstein ([email protected])

I tried two cameras and they both respond. Oddly, one is purpleish and one
makes it appear like a blue LED. Overall not very strong due to the camera's
IR filter. With a B&W video camera, response was quite strong that I can
point the remote at a wall several feet away and see the circle of light
produced. Most digital cameras have an IR filter built in. A few older
models had a weak or no filter and using an IR pass/visible light blocking
filter would produce some cool effects like white grass and trees.
John

 

[Don Klipstein]

Does anyone know the approximate wavelength over which IR LEDs that
are used on TV remote controls operate?

[snip]

The peak wavelength of those is usually 940 nm.

Thanks Don. Now if you happen to have a digital camera, turn it on and
point the tv remote to the camera's lens. Push a button and then look
at the camera's digital screen. They are visible through the digital,
which means the digital responds to 940nm!

Another LED nut, Craig Johnson (LED Museum), has a web page on infrared
LEDs, including some photos taken with digital cameras. He shows several
diferent wavelengths of IR LEDs, and the funny colors they appear to the
digital cameras that he used.

http://ledmuseum.home.att.net/ledir.htm

It turns out, my digital camera has enough sensitivity to IR to render
off-color (magenta-ish) glowing coals in a fireplace!

- Don Klipstein ([email protected])

 

[Travis Evans]

Another LED nut, Craig Johnson (LED Museum), has a web page on
infrared
LEDs, including some photos taken with digital cameras. He shows
several diferent wavelengths of IR LEDs, and the funny colors they
appear to the digital cameras that he used.

http://ledmuseum.home.att.net/ledir.htm

This is quite fascinating. I discovered several years ago that IR LEDs
in remote controls could be "seen" by our camcorders. Our current one
is especially sensitive when switched into "NightShot" mode, because
that's how it's designed--it uses IR LEDs which are mainly invisible
(except for the dim red glow I notice when they're on that I don't see
with ordinary remote LEDs) to allows shooting (black-and-white) images
even in complete darkness.

I've had interesting results looking at ordinary objects with NightShot
mode turned on. I assume that NightShot mode switches it into a
special mode where it effectively becomes an IR camera. The most
obvious is that red and white objects look nearly the same shade, so
red text on a white background (or vice-versa) become nearly invisible,
which makes sense because IR is close to red in the spectrum. I've
found some objects that appear dark in visible light but look very
bright with NightShot on. I've seen a dim gray background on the
vacuum-fluorescent display of a stereo system we had in the past that
didn't show up to my eyes (probably produced by the IR of the heating
filaments?). Before looking at the IR filter on a remote control, I
guessed that it would look clear in this mode since I knew the filter
was designed to block most visible light but pass IR, and I was
right--I turned on NightShot mode while looking through the viewfinder,
and I could instantly see right through all of these filters as if they
were crystal-clear.

It turns out, my digital camera has enough sensitivity to IR to
render
off-color (magenta-ish) glowing coals in a fireplace!

Last Independence Day I noticed something odd like this--a firework that
had just gone out seemed fuzzy and looked as if it was glowing a very
odd dim white color when I looked at it through the viewfinder (I was
not in NightShot mode, just ordinary visible-light color mode), and I
didn't see this color through my other eye which was not looking
through the viewfinder. It must have been the IR emitted by it.

 

[David Lee]

Travis Evans wrote...

I've had interesting results looking at ordinary objects with NightShot
mode turned on. I assume that NightShot mode switches it into a
special mode where it effectively becomes an IR camera.

Actually it's the opposite way around. All CCD cameras are sensitive to IR
and a conventional camera includes a filter to eliminate the effects of IR
radiation. A camera with "NightShot" mode simply has the facility to switch
out this filter - so it is an option with almost zero cost to the
manufacturer.

David