I am having an issue understanding the twins paradox and time dilation. If someone could point out where I have gone wrong it would be appreciated.

A light clock is often used to describe time dilation. It consists of a pulse of light bouncing between two mirrors, every time it does a round trip a second passes. Therefore a light clock that is in motion relative to an observer will tick slower than a stationary one, apparently due to the photons within the clock having a greater distance to travel through the clock.

So lets imagine the twins paradox occurring and each twin is given a light clock.

Before the Space Twin departs, both twins synchronise clocks.

The Space Twin then takes off, whizzes around at close to the speed of light and then returns to earth to compare the difference on their clocks.

Earth Twin says "100 ticks passed for me because I was looking at my clock the whole time and could see that the photons were travelling the optimum route through the clock at speed C"

Space Twin says "100 ticks passed for me because I was looking at my clock the whole time and could see that the photons were travelling the optimum route through the clock at speed C"

I don't see how this is consistent with the twins paradox, or the nature of light clocks slowing down due to time dilation.