Lots of drivers use fog lamps regardless of the weather but they are designed for use only in fog or heavy rain. The fog lamp control in the M series and Q70 series is on the turn indicator stalk and if it is switched ON, it will illuminate each time the headlamps are ON. If the Q50 series has a manual 'button' instead of the stalk switch, they may not be designed to stay in the ON position. Perhaps your owner's manual will explain why your car can't do this. I find it odd, but anything is possible.