Attach a light sensor to a servo, and then mount both servos physically in some sort of housing. Put the two servos fairly close together, as you'll eventually use the second servo to point to the light source that the first servo found, and if they're too far apart the geometry becomes complicated.

When building your chassis, consider the sense of the structure as a whole, as a composition, and not just its basic functionality.

Write software to sweep the servo with the light sensor from one of it's range to the other, and print out via the Serial monitor the minimum value seen (that's the brightest point), and at what angle it was found.

Be prepared to show off your construction in class, and submit your software here.