a project with light sensors.
1) the room
You could make an application that measures at which light level and individual turns on the light during the day.
Then make such measurements in at least a dozen different homes and explain the differences.
Knowning the right light level helps to automate room lighting.
2) street lights
Determine the ration between the time lights are on and that there is actually a person or a car using the light.
Dimming lights when no cars are around could save a lot of energy.
3) The vegetable test
use an arduino to give the vegetables in a fridge more light and check if vegetables in a fridge look better with or without light and which amount (and color) of light is the optimum. The color of light might differ per veg!
Use different colors of light to differentiate between different liquids (has been done so don't copy!)
5) Investigate light on bikes.
Is pulsating light better visible or not? and in fog? what is the optimal frequency / intensity / color?
now it is time for you to think