I want to control an external power circuit with Arduino Uno using PWM. The intention is to dim an external light bulb (which uses 220 ~ 240 V/AC ). I want to do this with my Arduino Uno. I've bought a relay (HL-52s v1.0) but discovered that I'm only able to turn the light bulb on and off. There is no way to use PWM and control the brightness of the bulb.
My question is: what kind of hardware is necessary to control the brightness of a light bulb which uses high voltages?