Among the examples of threejs I viewed that are related to refraction, all need a environment map, and the refraction effect is observed through camera directly. I wonder if there are tools available that can focus a spot light, or rectangular area light on a screen, such that the focused area on the screen is brighter than elsewhere. I need to visualize light ray beams before and after the focusing(refraction). I want to use Tyndall effect that purpose, but the effect itself may not be realized with existing tools in threejs.
This one does not require an env map: three.js refraction
Well, three.js is just a thin layer above WebGL. As long as you can implement an approach with WebGL, it should be possible with three.js, too.
Thanks for this advice. I thought that example is not real physical refraction. I will study this example in depth.