In the Advanced settings on my WiFi card I am able to set Transmit Power. The values are from 1 Lowest to 5 Highest.
What are the acutal values in miliWatt or dBm?
every device is different and you would have to look on the website or manal for that info mate.
the basic idea is a printer that sits 2 feet from your computer doesn't need to send it's wifi halfway up the street so save the power and don't have the next door using your printer.