Yes, You Need A Light At Night Along With Your Defensive Firearm

Positive Identification of a potential threat at night is vital, and for that you need illumination.

Otherwise tragedies like this happen:

10WBNS: Sources: Man fatally shoots 16-year-old daughter after mistaking her for home intruder

Mistakes like this continue to happen and there's absolutely no reason for them to happen.

"Know your target and what is beyond" is not just a suggestion. 

And before you get all "Hurr Durr a light will give away my tactical position."  You're likely in your house at handgun range.  You're unlikely going to be  acting like a silent ninja at 3am when you hear breaking glass or your home alarm goes off, more likely you're going to be stumbling around grabbing your stuff,  and making some noise dialing 911.   Walking around through a pitch dark house when you think there's an intruder somewhere there is dumb. There's nothing tactical about it.  

Pointing a gun at and pulling the trigger on an unidentified shadow is a recipe for disaster.

A good light will let you most importantly accurately identify and hit your target -- if such target even needs to be hit to defend yourself. As a potential bonus, a good quality light may even temporarily blind or disorient your opponent as well.

Have a light so you don't have a completely avoidable  tragedy.

 Take a low light shooting course, it's rather illuminating as to why you need a light and what a light can do for you.

Update:  Eaton Rapids Joe also offers some cogent thoughts on the matter.