Reckoning / Light
Room · wave 5
Light
Light runs straight until it meets something. At every surface part of it bends into the new material and part of it bounces off, and in glass or water each colour bends by a slightly different amount. This room traces rays exactly: Snell’s law is applied at the real curved surface, never a small-angle shortcut, and each surface sends back its share of light by Fresnel’s formulas. So, for rays in the plane of the drawing, what you see is what a lens designer’s software shows.
Refraction and total reflection
Snell’s law at one surface, how much light a surface reflects, the critical angle and Brewster’s angle.
Lenses
Converging and diverging lenses traced surface by surface: focal points, spherical and chromatic aberration, images.
Prisms and colour
Deviation, minimum deviation, and white light opened into a spectrum by dispersion.
Mirrors
Plane, spherical, parabolic and convex mirrors, and why a telescope mirror is a parabola.
The rainbow
One drop of water, one reflection inside, and the 42° circle that every drop paints.
Free bench
Put lenses, prisms, blocks, drops and mirrors anywhere, aim the light, and see what happens.
How the bench works
Every ray starts at a source and is followed from surface to surface. At each one the program finds the exact point where the ray meets the surface and the surface’s normal there. It then applies Snell’s law to get the refracted ray and Fresnel’s equations to split off the reflected one. Past the critical angle nothing is transmitted and all the light is reflected. A ray’s brightness on screen follows the share of light it carries. White light is traced as twelve wavelengths from 405 to 680 nm. Indices come from published dispersion formulas: the glass maker’s data for crown and flint glass, Malitson for fused silica, Daimon and Masumura for water, and Peter for diamond. The code is checked at every build against published indices, closed-form results and an independent paraxial calculation.