In Microspeak, a feature lights up if it becomes available in an application when run on an operating system that supports it.

The idea is that you write your application to run on, say, Windows versions N and N + 1. There is a new feature in Windows version N + 1, and new functionality in the application when the code detects that the underlying Windows feature is availble.

Here are a few citations:

I have had some requests lately for details on the path to Windows 7 compatibility and how to light up key features.

Top 7 Ways to light Up Your Apps on Windows Server 2008.

The idea is that the program takes advantage of new Windows features when running on new versions of Windows. if run on older versions of Windows without those features, nothing happens.

Inside the product group, discussion about “lighting up” often takes the form of deciding how much new hotness will be automatically applied to old applications and how much needs to be explicitly opted in. Applying new features to old applications makes the old applications and the new feature more valuable because the user sees the feature everywhere, as opposed to working only in new applications designed to take advantage of it. On the other hand, applying them automatically to old applications creates a compatibility risk, because the application may observe a behavior that hadn’t occurred before, and it may begin behaving erratically as a result.