Calibration and Ambient Light Sensor

I'm an graphic designer and i work on my laptop in controlled lightning, so i don't need the ambient light sensor. I calibrated my display to a fixed level of brightness and with the sensor off in display preferences. But after a while the leopard kicks on the sensor and screws my calibration. I'm forced to recalibrate the display because i can't be sure what was the reference level of brightness. It is a way to force os to keep the sensor off?