If i give 30% duty cycle then for 30% it will take full power that is same voltage and current.
but is off for 70%.So power delivered to LED is averagely 30% right???
Yes, the
average power over time is 30% of what it would be at 100% duty cycle. The
instantaneous power is either 100% or 0, depending on when you look.
Then is there any affect on current???
As i think i am delivering same current for LED for 30%.
Which current are you asking about? The input current to the driver will be on and off, just like the output current. During the on time, the input and LED currents should be the same as they would be at 100% DC. During the off time, the input current should be very small (essentially zero) and the LED current should be zero. For estimating forward voltage and tint shift, you should use the instantaneous current. For calculating heating and battery loading, you should use the average current.
This is how PWM differs from 'analog' dimming, where the current is on all the time but the current value is changed. When using analog dimming, you use the same current value for all estimates and calculations. This is why the tint doesn't change when using PWM dimming, but it does when using analog dimming.
And again i have doubt that will it change color temperature.
PWM dimming should not change the color spectral output of the LED. Analog dimming WILL change it, but the effect is pretty small until you get to significantly lower output. Depending on the LED and the application, you may get well below 10% before noticing much change.
You should be careful to select a driver built for PWM dimming, and select the proper frequency. Some drivers don't work well with PWM at all, and some don't like high frequencies.