controlling a light fixture with a wireless switch
There are numerous solutions. 

One common approach is remote wireless switches coupled with matching receivers, such as the LevNet system. You hard wire a receiver near the load and mount a wireless (and in some cases batteryless) switch remotely. The distance the devices work is limited (usually 10 to 20 feet) and they tend to be expensive, in the $200+ range per circuit. These systems tend to be proprietary and usually only work with their own brand or a licensed affiliated brand.

A second approach is the wireless hub type system, such as the Wink system. These use an open protocol, such as Zigbee, that can link numerous devices, including single bulbs. The control may be dedicated or can work on a smartphone, a tablet, or a computer. The cost of the hub may run from $50 to several hundred dollars, but the remote devices are often fairly cheap. Introductory specials have featured two smart bulbs and a basic hub for $50. Unlike proprietary systems, you can often mix devices from various manufacturers.

If you search for wireless switches and wireless hubs you will find a number of choices.