Light sensitivity and noise
1ISO is the control that allows you to set the sensitivity of the camera sensor to light. Lower settings make the sensor less sensitive to light, while increasing the ISO makes the sensor more sensitive to light. So as a rough guide, this means that lower settings can be used in bright conditions or when you have a tripod to support the camera. Higher settings are almost always used to achieve a shutter speed that’s fast enough to allow the photographer to handhold the camera in low light, or to freeze a moving subject with a fast shutter speed. However, the downside is that as you increase ISO, more noise is introduced to the image, which ultimately diminishes image quality.