how do you take light photography on a nikon D3100, HELP!?!
All photography is light photography.
Good enough? Let me put it this way: it might be too good for a beginner, unless the beginner is eager and willing to learn to use it properly. As for sample shots from this camera, they range from the truly admirable that have a professional look to flawed snapshots. It all depends on the skills of the person pressing the shutter release.
Set your camera to manual. Use an esposure of ISO 200, F 5.6 and a Shutter speed of about 8 seconds. Make sure it isn't set at 1/8 of a sec. Also use a tripod or stable surface. Push shutter, do the light graffiti, and check it out. If it is too bright, change the f stop to f 8 or f 11. If it is too dark, change your ISO to 400 or 800.
Light painting is done by putting your camera in bulb mode and holding the shutter opened while you write with your light or the light moves by you. You'll need a remote or you will see the shake from holding the shutter down. Start out with ISO 100, f/5.6 and bulb for your shutter. Test it out to see what your exposure on the light looks like. If it's too bright raise the aperture up accordingly. If it's too dark you may need to raise your ISO up some. You can lower aperture if possible/depending upon your lens
