Does the incidence angle and refraction angle have to add up to 90

[applestrudle]

does the incidence angle and refraction angle have to add up to 90

I'm trying to figure out the geometry of thin film refraction!

 

[nasu]

Not in general. They don't have to.
They do add up to 90 degrees when the angle of incidence is the Brewster angle and the reflected light is fully polarized.

 

[sophiecentaur]

does the incidence angle and refraction angle have to add up to 90

I'm trying to figure out the geometry of thin film refraction!

Where did you read anything to that effect? Snells law doesn't lead to that general conclusion, does it? Are you referring to a certain, special situation?