# Total internal reflection zero

## Main Question or Discussion Point

How is that in refraction of light energy is lost but not in case of total internal reflection?
Is the loss in total internal reflection exactly zero?

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Energy is never lost.

In refraction some of the light is reflected and some transmitted. If you only measure the transmitted light, you would measure an energy loss.

In total internal reflection you are measuring the reflected light, which is equal to the total incident energy.

why is that in refraction both refraction and reflection takes place but in case of total internal reflaction only reflection takes place but not refraction?

sophiecentaur
Gold Member
On a possibly superficial level, it's because Snells Law applies and the Sine of an angle can't be bigger than 1. That means there can't be a refracted wave and all the energy has to be reflected.

Andy Resnick
How is that in refraction of light energy is lost [...]
Why do you claim this?

On a possibly superficial level, it's because Snells Law applies and the Sine of an angle can't be bigger than 1. That means there can't be a refracted wave and all the energy has to be reflected.
In other words, light changes direction when it changes between different mediums. If in this change of direction it happens to point back away from the medium (because of a very acute angle) then it never travels on a line that goes through the medium.

This is what makes water appear to twinkle, flashes of total reflection as the water positions itself at this acute angle with incoming light.

sophiecentaur