Illuminated lights below apps

I have recently noticed that many of the "lights" below the various apps in the dock are illuminated when I am not even using these apps. I normally only keep 3 active - mail, calendar and notes, but 12 others are illuminated.None of these are set to open at login. Any ideas please?

You are not properly quitting your apps, you are just closing the active window using the "red dot." Stop doing that and get in the habit of using "command-q" or "file-quit" when you are done with a program.

If having all those apps isn't causing you any issues, i.e., slow downs or anything its nice to have them "running" but not visible since if you click on the icon the window will appear instantly as opposed to going through the application loading time..

Otherwise, as chas_m suggested, properly quit the application and those lights will go out..

Thanks Chas_m & RazOrEdge, that has corrected the problem immediately and I note RazOrEdge's comments about keeping apps open if it does not slow my Mac down.
Interestingly the Apple store where I purchased my machine could not tell me how to overcome this issue!

Glad we could help and I'm a little surprised that the Apple Store folks couldn't help you with this trivial piece of functionality that has been there forever..