A popular circuit for electronic hobbyists called a "Joule Thief" has been making the rounds on the Internet.
When your batteries go dead, there is still energy or "joules" still left in that battery. Instead of simply tossing it out to get recycled, why not squeeze out the remaning joules of life to do something useful.
With the Joule Thief circuit you can light a white led till the battery is down to .2 volts. Use it for a night light, it will run for days. Then, when it is good and dead, give it to the trash collector to get recycled.
Here is a good modification you can do. Change the 1k resistor to something around 2.2k to 10k and place a CDS light sensitive resistor between the transistor base and emitter (or use a trimmer). This mod will make the circuit light sensitive and cause the circuit to shut down during the day. When its dark , the white led will light. Now how about that for a proper night light!
So go ahead and google "joule thief" and see what you can find, then make your own artbot.