Invisible Smartphone Light (IR)?

So I noticed something odd about my phone and I haven’t been able to find an explanation through Google.

When I point my Webcam at my phone, I notice a little blinking light just right of the front camera which seems invisible to the naked eye. It’s separate from the notification light which is further to the right.

What could it be? The phone is an LG G5.

could very well be IR for autofocus.


It’s an infrared lightsource. It’s for the autofocus and is also a rangefinder for detecting if the phone is in your pocket. If you use the in pocket detection for turning your screen off it uses the ambient light sensor and the infrared light source. If the sensor doesn’t get anything back and it’s also just generally dark the phone assumes it’s in a pocket or purse.


What @LDoBe said. Point a TV remote control at your phone or camera and press the button. You’ll see the IR light blinking.

Ah, but see, it’s basically blinking all the time. Right now, for instance, it’s just sitting on the desk, and if I point my webcam at it I can see the IR light blinking.

Wonder what that does to the battery life… my guess would be not too much, since lower frequency = lower power, right?

It’s probably using about the same amount of power as your notification light. So negligible.


Hmm, only a few phones have actual ‘IR blasters’ to enable universal remote functionality… I wonder if it’s possible to employ the autofocus LED in the same way.

The lack of an IR receiver wouldn’t prevent learning codes, since the camera can pick those up.


I think my phone has the ‘IR blaster’ too… although that’s on the top side of the phone; the IR proximity sensor, if that’s what it is, is on the front.


The LG G5 does have an IR blaster, and it’s mainly meant to be used as a TV remote, or possibly for communicating with other phones.

The Samsung Galaxy S5 had one on the rear of the phone. It could control TV and other IR-remote devices, as well as take your pulse, and was decently good for illuminating the field of view for my night vision monocular.

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Take your pulse? How’s that work?

It’s interesting to me that the dirt-cheap usb webcam picks up infrared… from what I understand that’s a sign of its cheapness though; lacking an IR filter.

I wonder if I pointed it at the coils on my electric stove, if I would see something neat. Unfortunately I don’t have a laptop or anything to bring it close enough to conduct that experiment.

You stick your finger over the blaster, and it gauges the periodic change in density of your skin as blood pumps in.

You won’t. The thermal IR band is roughly 9,000–14,000nm, the wavelengths your camera sees is generally starts around 800-900nm and gets shorter from there. So you can’t really “see heat” unless the thing is so hot it’s radiating in the visible spectrum already.


We do have options for pretty cheap thermography though.

The Seek Thermal camera is a ~$250 USD attachment for smartphones that can give you a thermal IR image at 12 frames per second with a resolution in the ballpark of 176x96 pixels.

FLIR also makes something like that, but it’s self-contained and a lot more expensive.

Thermal imaging is very expensive, and Seek Thermal is an order of magnitude cheaper than anything that existed previously.


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