Low light is always going to be noisier. You need a certain number of photons on the pixel to get a good signal. In the Sensor World, we talk about Signal to Noise (SNR) and you need a minimum SNR to make a good measurement, which is what you are effect doing when you take a picture. Any detector has noise, and the signal that you want to see has to be above that by some level before you 'detect' it. You can increase the exposure time, but that increases the chance of causing blurring in the picture. Are you shooting in Manual or Auto? You didn't say how the pictures look in 'bright' light (i.e. full sunlight).