Film Speed
Film speed is a number that tells you how much light a roll of film needs to make a clear photo.
Think of it this way
A thin sponge in a bowl soaks up water fast with just a few drops. A thick sponge needs lots of water poured on it to get fully wet. Fast film works like the thin sponge — it only needs a little light. Slow film is like the thick sponge — it needs a lot of light.
Explaining film speed by grade level
Some film needs a lot of light to take a good photo. Other film works fine with less light. The number on the film box tells you which kind it is. A big number means the film can work in darker places.