It'll also leave a lot of artifacts that you don't want if you try to up the ISO in low light - 1600 ISO would leave you with a very grainy image in low light - better, if possible, to reduce the shutter speed or aperture in bright light and reverse that in low light, leaving ISO as low as possible...

Each step in ISO, 100, 200, 400, 800… is equivalent to a stop of light, like your f-stops. E.g f-11 at ISO 400 is same exposure as f-16 at ISO 800 or f-10 at ISO 200.