Short distance Light beam control (10cm) - what is best to use in On/Off mode?

[flotulopex]

Sorry, I don't understand your comments...

What's a carrier?

Why working on the LED's power?

What are the bigs?

[mister_e]

Carrier = Porteuse (ou fréquence porteuse)

Roughly, it's the frequency you modulate your signal. like an FM/AM radio station.

Why playing with the Power of the LED... more power (current) = usually better range, lower power, lower range.

[skimask]

Sorry, I don't understand your comments...
What's a carrier?
Why working on the LED's power?
What are the bigs?

Carrier - the underlying information mode of transport. For instance...air is the carrier for sound waves, we modulate the air when we speak. Like AM radio, 900khz is the carrier, which we modulate the amplitude of to get the audio information from. Make any sense?
With an IR LED, the way it's most commonly done is to modulate the IR LED with a ~38Khz signal, then turn that whole signal on/off and a certain rate.
If you've got one IR LED working at 38khz and another one next to it working at say 50khz, the two probably won't interfere with each other as opposed to having two of them modulated at the same frequency next to each other.
A good example would be you and wife going out with another husband/wife couple. Both him and his wife are talking at the same time, both are transmitting different modulated carrier waves (sound), but you're only tuned into him, and that's easy (maybe 'cause it's easier for the guys to tune out the girls sometimes! ...oh that's gonna start something I can feel it now! ). If you were in that same situation talking to 3 other guys (with similar voices), it would be a lot harder to figure out who's talking to who.

Power - maybe because some of the light might spill over to other IR detectors...

Bigs - fixed it...should have read 'How big are the boxes themselves?'