Some cities hang their traffic lights from left to right, rather
than from top to bottom.
Explain why this might cause a
problem for a driver with red-green perception deficiency.

The angle and location

Explanation:

There are some who can't perceive the order of red and green together. Having it angled up and down is safer because you know out of common sense that red is on top and green is on the bottom. Having it sideways makes the light elevated on the same level, deceiving the eye better.

i would say it is

the electromagnetic energy from the sun arrives in the form of visible and invisible light.