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Inside the TV Remote we have a LED of infrared light which sends commands to the TV.

Isn't it influenced by the light of the room(if any?).I thought if an electron in the valence band absorbs a photon with energy greater than the band gap the electron goes to the conduction band and a phonon is emitted.

Photons of 'infrared light' have less energy than photons of 'visible light' so even if the LED doesn't emit anything the sensor in TV should still be 'activated'.What am I missing?

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    \$\begingroup\$ if you follow your line of thinking, then you should be asking why our eyes see our surroundings and not a complete whiteout \$\endgroup\$
    – jsotola
    Oct 10, 2020 at 23:40
  • \$\begingroup\$ @jsotola it is not the same thing with your example \$\endgroup\$ Oct 10, 2020 at 23:41
  • \$\begingroup\$ I have LED bulbs in one room that do interfere with an IR remote. The remote receiver is much less sensitive when they are on (even compared with daylight) I guess their PSUs switch somewhere close to the 38kHz modulation frequency used by the remote... \$\endgroup\$
    – user16324
    Oct 10, 2020 at 23:43
  • \$\begingroup\$ I once had a CFL that would change TV channels when switched on ! \$\endgroup\$ Oct 11, 2020 at 2:13

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Yes, the sensor responds to the room light and it may be brighter than the signal from the remote control.

The signal from the remote control however is modulated with a signal that is typically at 38kHz. The TV is tuned to only respond to light modulation at that frequency. The 38kHz modulation is pulsed to transmit the actual control function.

The signals from room light will typically be at DC for steady light such as sunlight or at 100/120Hz from lights powered by the wall socket (the ripple is at twice the frequency usually because the lights illuminated on both positive and negative half-cycles). Some LED lights may modulate with other frequencies as well because of the way they control their power.

TV Remote Control Formats

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  • \$\begingroup\$ Can't we use ultraviolet light for the communication between the remote control and the TV sensor to avoid confusion in the external signal? \$\endgroup\$ Oct 10, 2020 at 23:48
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    \$\begingroup\$ @ArtOfElectronics - UV is not so easy to create and receive (ie more expensive). Infrared works fine it is rare for there to be any interference and it is non-critical even when there is. Some remotes use radio. \$\endgroup\$ Oct 10, 2020 at 23:51
  • \$\begingroup\$ But there are LEDs which emit UV light and photoresistors which work with UV light correct? \$\endgroup\$ Oct 10, 2020 at 23:55
  • \$\begingroup\$ Infrared LEDs were invented before UV LEDs and in the 1960s started to replace acoustic communication in remotes. IR is also safer than UV. Most likely you could use UV, but what would be the reason? Especially knowing kids will try to look at the LED output so it would not be safe. \$\endgroup\$
    – Justme
    Oct 11, 2020 at 0:13
  • \$\begingroup\$ NUV light is not dangerous EUV is dangerous. \$\endgroup\$ Oct 11, 2020 at 0:22
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What you seem to be are missing is the information how IR receiver modules work. For more info I suggest reading datasheets and application notes of such modules, but here is a short version.

The infrared receiver module is typically molded in plastic that filters visible light and passes infrared light. So the amount of visible light outside the infrared wavelengths in the room does not have a significant effect.

Even if there is infrared light in the room, the receiver module filters ambient light away, most likely by AC coupling the preamplified PIN diode signal.

Then, there is a bandpass filter tuned to the infrared carrier frequency, so that for example a 38kHz IR receiver will ignore disturbances from for example fluorescent lights dimmed at 100kHz.

Then there is also an AGC circuit to monitor the 38 kHz light levels. Any steady state or slow disturbance at 38 kHz carrier frequency is filtered away and only actual 38 kHz short bursts from remote is enough to exceed the baseline and detected as a transmission.

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Your IR receiver only responds to changes in signal. Any 'normal' light is treated as 'quiescent', like a DC offset.

You need some meaningful pulse train to activate the receiver.

FWIW, a failing CFL lightbulb sometimes triggered my TV to change channels when switched on because of the rapidly varying light output.

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