I need to prepare a simple circuit . For an exhibititon so I need some clues plz guys help me?

Added 3+ months ago:

The circuit must be simple and clear . As it would be made by my little sister. Other than that simple logic gates too must be addded to this circut tooo also I neeed a clear and simplest way to expressss It plz help me to deal with my problem

Added 3+ months ago:

Also I too need a clear explanation throughout my development of the prototype considering alll the above facts I too bought a set of bulbs and a single pair of Ldr soo alll my money must not be wasted therefore. Also I tooo have some doubts too in my project too as she has recived a little prototype to be developed I tooo need to exprees the advantages of the above prototype also I have a question with me old this prototype suit or fit in under the catogery of svientifi and technical researches can anyone sen linkk to me

Added 3+ months ago:

The total results must be gained by alll ma effforts