Above are the Wigton lights on ISO 100.
Now it is ISO 200.
Finally ISO 400.
If you double the ISO, you double the sensitivity to light. Hence you need half the light to take the same picture. They say that means the exposure time is less. I am certain that the exposure time was longer on ISO 400. It may be that some of my other choices meant that it wasn't a fair test (I had it on a night setting which must surely give a longer exposure). One article I read said that increased light sensitivity on a digital camera just means amplifying the signal more. Hence the noise is amplified as well and the picture isn't as sharp. That's certainly true. They also say that noise affects smaller pixels more. My cheap camera is small so the pixels on my CCD won't be very big. I'm beginning to get the hang of it but still more work needed.
