Can I make a trigger activated by light?

Sorry, but your question is too broad, and this is not the place to ask for scripts. Unity Answers and its community is here to help you solve any Unity-related problems you have, not give away free code. If you don't know how to write code, I suggest learning Unity's Java Script (its really easy), but if you don't have time, or whatever, then you can try asking your question on the Unity Forums. I hope you can get an answer!

Also, use google. Do tutorials, and learn how to use Unity.

Here is a list of tutorials to get you going :

Start at the bottom and work up : http://www.unity3dstudent.com/category/modules/

this is the YouTube link for the above as one playlist : http://www.youtube.com/watch?v=-oXYHNSmTxg&list=PL27B696FB515608D2&feature=plcp

the Unity Wiki : http://wiki.unity3d.com/index.php/Tutorials

A list of resources : http://answers.unity3d.com/questions/12321/how-can-i-start-learning-unity-fast-list-of-tutori.html Helpful page with information on using Built-In Arrays and Lists :

http://www.unifycommunity.com/wiki/index.php?title=Which_Kind_Of_Array_Or_Collection_Should_I_Use?

The unity wiki link above is very handy with lots of scripts and shaders too (just check out all the links down the left, and the tabs along the top : http://wiki.unity3d.com/index.php/Scripts )

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Here is a video on using Unity Answers : http://video.unity3d.com/video/7720450/tutorials-using-unity-answers

the FAQ appears just to the right of this page also : http://answers.unity3d.com/page/faq.html

also : http://answers.unity3d.com/questions/133869/how-to-ask-a-good-question.html