There are many uses for resistive dividers (basically 2 resistors in series). Generating a (not so accurate) reference is one of them. Using a resistive sensor is another.
There are many types of light sensors, do you know which type you have? Do you have the datasheet for it?
Most common types are photo-resistors (resistance change based on light), photo-transistor (current change based on light), and photovoltaic cells (voltage change based on light). They require very different circuits, and behave differently.
It's unusual to use a digital input to read from a sensor. Using an ADC input would make more sense.