Hi everybody,
I am trying to control the intensity of a lamp.
I have already done the blink of a lamp by using MOC3021 (optocoupler) and BTA41-600B (triac).
And I have already tried to control intensity by using above elements and 4N25 (optocoupler) by zero-crossing detector. But till now I am trying.
So I am requesting to help all of you.
Thank you.
Kali..
If your power is 50 Hz you have half a wave every 10,000 microseconds. You want to turn on the Triac early in each half cycle for bright and late in the half cycle for dim.
I would use one of the timers to turn on an output when he timer reaches the value in one of the Output Compare Registers. Turn off the output and re-start the timer when you detect a zero crossing. Chage the value in the OCR to change the brightness.
In the search box in the upper right handside of this forum page type AC Lamp Dimmer.
There are a number of projects that have done what you want to do. 
Tom