Data sheet time.

http://www.mouser.com/ds/2/389/DM00095160-490569.pdf
Page 1 top right. Rds .165 ohms. This is the resistance of the FET when it is turned on hard and it's temperature is 25C. As a matter of note almost all the specs are at 25C.
Table 3 shows the temperature rise per watt in the FET. So with no heat sink it's temperature will rise 50C per watt.
You have 8 watts - 7^2 X .165 ohms. So it would go to 425C (if it could)
Then if you look at Fig. 11 it shows what happens to Rds on with temperature. Over 2 X higher at 150C. So suddenly the resistance is .33ohms. So now you drop 2.3 volts across the FET instead of 1.15. At 450C things are melting.

You could use one like this:
http://www.mouser.com/ds/2/200/irfp4110pbf-82436.pdfThen Rds on is only .0045 ohms - .22 watts.

 

I'm not sure why you want to using the reverse way to control the mosfet or IGBT, but here you haven't given the enough Vge for IGBT, the Vge should be >=15V.

The normal control method was shown on #16, input high then turn on the mosfet, that's a quite normal method and save the energy, could you tell me do you have any special reason to used that way to control?

What's difference between that using zener diode and the voltage divider to supply the power, when the input voltage varies then the output voltage will be follow the changing, that's your circuit did, but when you using zener diode then the output voltage only just has a very small changing.

I changed the vdivider to supply 15 when using the IGBT.
It is not that i want to use this method - the inverse relation to PWM and bulb power, it was a method i used before that was documented in a datasheet.
So i used it, and it worked.
The reason i have stuck with my V divider and inverse relation configuration is because i do not have a zener or suitable BJT as stated earlier.

 

Data sheet time.

http://www.mouser.com/ds/2/389/DM00095160-490569.pdf
Page 1 top right. Rds .165 ohms. This is the resistance of the FET when it is turned on hard and it's temperature is 25C. As a matter of note almost all the specs are at 25C.
Table 3 shows the temperature rise per watt in the FET. So with no heat sink it's temperature will rise 50C per watt.
You have 8 watts - 7^2 X .165 ohms. So it would go to 425C (if it could)
Then if you look at Fig. 11 it shows what happens to Rds on with temperature. Over 2 X higher at 150C. So suddenly the resistance is .33ohms. So now you drop 2.3 volts across the FET instead of 1.15. At 450C things are melting.

You could use one like this:
http://www.mouser.com/ds/2/200/irfp4110pbf-82436.pdfThen Rds on is only .0045 ohms - .22 watts.

Concise, thanks alot!
I couldn't spot the temp rise per watt when i looked last night.
Ill get reading on the specs to better understand the issues at hand here.
Thanks for that link - greatly appreciated! - i have ordered the mosfet you linked