How to change the video quality on my nikon d5000?

I'm using the d5000 for a while now and I just love the image quality it delivers.
But when i look up nikon d5000 video test, I see video's with awesome video quality too.
But whenever i record video it comes out rather low quality and grainy.
I've look through the settings and the quality settings are on 720p but it still records grainy video's.
How can i change this?

Not possible
just use good lighting