# Contributions and brightness

### Exploring two paths

Set up waypoints to define a path for the photon to explore. Note the contributions of each path. See how the expected brightness changes.

As it's only the difference in trip time between the paths you can freeze

the spinning without changing the predictions.

### Exploring four paths

Now that you're familiar with the ideas, you can try again with four paths. Four paths is still a simplification because each photon explores all paths, not just a few.

### A photon explores a space

- create waypoints to define the paths
- a photon explores all paths
- each path contributes the detector, set by the spinning of the arrow and the trip time
- add the contributions to predict the chance a photon ends up at the detector
- if the chance is high, then many photons will arrive, and it'll be bright.