Here are the premises:
There are two pictures of the same location. Both are taken at night but one is dark and the other one shows all the light sources. There is also two images of a light switch. One is showing the switch in the OFF position and one is showing it in the ON position.
When the user comes to the webpage, it will show the dark picture and the light switch in the OFF position. If the user clicks on the light switch it will change to the ON position and the picture will gradually fade to the light picture, creating the illusion that the lights are turned on. If the user once again clicks on the light switch, it will shift back to the OFF position and the picture should fade to the dark picture.
This should be programmed as a module, since it will be used on more than one page on the web site. And the pictures will also change.
At the moment I have a module from jxtc that can be modified, to save time. For an example look at http://dev3.xtnd.se