Can anyone tell me please.

I use a Samsung Cam recorder. I haven’t any problems using it in the daytime, but when it comes to videos at night I seem to end up with less than average footage. I often video an Artiste on stage and the reproduction is not as it should be. I have a couple of times recently noticed other people using a video with a small light producing, gadget on the side of the cam video. Has any one any experience of these? and is it a part/extra that can be purchased for an existing model. Plus if so is the reproduction worth the investment?