How are you powering your LED?
Can you please post a copy of your circuit, in CAD or a picture of a hand drawn circuit in jpg, png?
Can yu post a picture of your project so we can see your component layout.
LED like that really needs a current controlled driver, 100W.
If you are using 12V supply you need it to be able to supply…
P = V * I
SO I = P / V
I= 100 / 12 = 8.33A
The sparkfun device does not have the current carrying capacity.
You can't properly drive an LED with a constant voltage and a MOSFET. LEDs are driven from a constant current source. You can buy a [u]constant current LED supply[/u] or you can build one, but they are not easy to build. (A regular little LED is current-controlled by a resistor. But, you probably don't want to use a ~100W resistor in series with your 100W LED.)
The industry standard for dimming control is 0-10VDC or 10V PWM, so if you by a dimmable power supply you'll still need a small transistor or MOSFET (and an ~10V power supply) to "boost" the Arduino's output voltage.
Could anyone tell me how to calibrate a led curve? or should I try everynumber 0-255, then try different arrays and work with that?
The "curve" probably isn't the issue. When step from 1 to 2, that's a 100% increase, and you might notice the change. A step from 254 to 255 is less than 1/2% and you probably won't see it.
I have tried, using a low pass filter circuit. that didn't work either. Should a DAC which converts pwm to analog voltage be better option?
Analog into your MOSFET won't work because if the MOSFET is "half-on" it will overheat. 16-bit analog or 16-bit PWM into a constant-current supply would give you more resolution. (With 16-bits you have 256 times as many steps... More than 60,000 steps.)
This 100watt COB LED (10101watt LED) needs ~33-35volt, with a constant current of 3Amp.
Not sure what you were thinking there (300mA).
"My power supply is rated 12V 120W, and I have added a booster to get 30V, less than 100W".
Needs to be 36volt minimum for the LED and the losses in the driver, and capable of 3Amp.
"Currently, I have arduino mega, connected Pwm pins to mosfet, which controls the led chip."
A "LED chip" (like the ones from Sparkfun) already have the switching circuitry onboard.
Adding a mosfet is wrong.
"The LED also needs a heatsink!"
Yep, a beefy CPU cooler with fan is needed for a 100watt LED.