This is really just an illustration of how the Internet just works.
Houses have light switches. But can Second Life houses have light switches? I'm in the dark about this (ha ha), but let's try 'remote light switch second life' in Google.
Here's not only the code I need but also two YouTube clips with the author's Avatar demonstrating how to do it. So I can download the code, Cut&Paste it into a Script holder in Second Life, and there it is.
Oh. One alteration required - American light switches are upside down. Easily changed...