1. A sensor device, comprising:
a light sensor that acquires a first light quantity measurement value that is proportional to a light quantity of a backlight
and a first measurement time;

a light quantity target value calculating unit that calculates a light quantity target value based on a user setting for the
backlight;

a measurement time calculating unit that calculates a second measurement time for when the light sensor acquires a second
light quantity measurement value a next time, based on the acquired first light quantity measurement value and the light quantity
target value;

a normalizing unit that divides the acquired first light quantity measurement value by the first measurement time, to obtain
a normalized light quantity measurement value; and

a light quantity reference value setting unit that calculates an absolute value of a difference between the normalized light
quantity measurement value and the light quantity target value.