Linear/exponential Curve for white Leds

[totoetlititi]

Hi, I'm trying to control a set of white dimmed LEDS with ESA2 and a stick gu2 interface.
Because the product is not listed in fixture library, I'm using a "generic par36" fixture.
The main difficulty is that the perception of LEDS white color is not linear. It means that using a fader from ESA2 interface works:
- at a value of 0, LEDS are black,
- at a value of 255, LEDS are full white.
But at a value of 127, (so half fader position), LEDS are are not between black and white, they are stil very dark.
Fader value has to be close to 200, to perceive LEDS half dimmed.
I did not find a way to deal with that, and the result is all effects and animation made with the Scene Builder application are wrong.
Maybe the fixture is wrong, what could you suggest to use instead ? There are simple white leds, without any fancy stuff...!
Is there a way to configure/change the linear curve of dimming for a fixture ?

All the best,
_TG