Interference filter

So, imagine you have a bunch of different colored toys, like red, blue, and green blocks. And you want to only see the green blocks, because those are your favorite.

An interference filter is like a special pair of glasses that can help you see only the green blocks. It does this by blocking out all the other colors of light, so only the green light comes through.

It does this by using something called interference, which is like when two waves (like ocean waves or sound waves) meet and either get bigger or cancel each other out depending on how they line up.

The filter has a special coating on it which makes it so that only green light waves line up in just the right way to get through. All the other colors of light waves are either too big or too small to line up just right, so they get canceled out and don't come through the filter.

So, when you put on the interference filter glasses, everything that's not green gets blocked out and you only see the green blocks. Yay!