What's the difference? 35mm 200 speed, 400 speed, and 800 speed. what's best for what?

Question

What's the difference? 35mm 200 speed, 400 speed, and 800 speed. what's best for what?

Answer 1

For a sunny day, ISO 100

For a partly cloudy day, ISO 200

For windy/overcast days or action, ISO 400

For low-light, non-flash, ISO 800

Answer 2

The ISO (film speed) is the film's light sensitivity... for sunny days 100-200 is pretty good, for dim lit situations 400-800 is pretty good.