Nikon d5000 video seems grainy?

When I try to film using my d5000 I noticed that when i'm shooting video it sometimes looks a little grainy, and not as "HD" or clear as it should. How do i fix this? What settings do i need to change? And what.

Grainy = not enough light. Solution = Add light.

Remember, your D5000 is a dSLR. It is designed to capture still images - and does that well. Under low light conditions, use of a flash is strongly recommended. Video capture is a secondary "convenience feature". That is not to say it can't capture video well - it can, but this was not a primary design consideration. Under low light conditions, the flash will not provide a long enough "stream" of light to illuminate what you want. Adding light will remove the noise. If the scene needs to be dark then learn to use "day for night" tricks when editing the video.

Link to the camera's manual:
http://www.nikonusa.com/...000_en.pdf

Other items to consider when using the video secondary feature:
Page 3: built-in mic location. Item 3. This is a mono mic. Page 51.
Page 50: video file size limitation/segmentation.
Page 51: Overheating potential. Cool-down takes a LONG time.

There's no mic jack so external mics can't be used. As well, there's very limited manual audio control. Which is fine - an external audio recorder like a Zoom H2 or H4 should be used, anyway…

Clarification: The Nikon D5000 is a digital SLR. There's no film involved - it captures video or still images. Both still images and video are stored/captured on flash memory.