ISO is a measure of the film’s sensitivity to light. The lower the ISO the less sensitive it is towards light. The higher the ISO the more sensitive it is towards light. This of course comes with a trade off, quality. Generally the higher the ISO you use the lower the quality of the photo. In digital photography you introduce a photographic element called noise or grain when raising the ISO sensitivity. When you want to achieve the highest quality possible, you want to the lowest ISO possible. Most cameras shoot at ISO 100 while some can even go as low as ISO 50.
Shooting low ISO is great when you have high quality light sources such as a flash, strobe, sun, or even a light painting tool like an LED to help you out. Low ISO can be considered anything from ISO 50 to ISO 400. For our purposes at LightPaintingArt.com, most of the photos use low ISO in dark areas so that shutter speed can be slowed down to several seconds or minutes at a time.
Why would you use low ISO when you’re shooting in almost pitch black you ask?
Well combine high aperture (f/8 – f/32) and long shutter speeds (13 sec, 30sec to BULB) and it’s the perfect combination to capture great light paintings.
Shooting high ISO is great when you are shooting in very low light conditions such as a club, a dimly lit restaurant, or even the sky at night. Sports photography is another use for high ISO because it allows you to use a faster shutter speed to capture motion without sacrificing exposure. In the digital age high can be thought of as ISO 1000 to ISO 3200 or above. The technology that sits in professional bodies have even proved to shoot “usable” images @ ISO 128,00+.