IR couple? What should I take in account choosing ones?

[rikotech8]

Hello everyone!

My new project requires, remote controlling relays. I chose to use IR emitter-receiver couple. Since I have never had something to do with IR sensors, I am asking you for help.
Here is my question:
What characteristics (e.g light wavelength, power, type etc.) ought to match, in order to make them both to get along each other (send/receive data correctly, at max distance with minimum power - rude said )?
I know it is not a rocket science, but I don't want to buy these staffs several times. I have been there.
Thank you.

 

[D.A.(Tony)Stewart]

max distance with minimum power can be traded off with speed of data and modulation.

IR wavelength does not matter much as long as receiver bandwidth includes transmitter and you have a daylight blocking filter.

Path loss is inverse squared, so smallest beam angle in emitter is desirable

Power per bit can be computed as VI*t from transmitter but receiver sensitivity is highest with remote control type used in Kopters and TV's