THE WORKING
NOTEBOOK.
A practical guide to using the images and the light model without confusing an observation with a measurement.
Describe before you explain.
Begin with a sentence that only names what is visible. “A bright line follows the edge of the gold” is an observation. It is different from a claim about the age, value or manufacture of an object.
Choose one of the seven studies and list three details: a boundary, a repeated shape and a change of brightness. Then enlarge the image. Does the order of your observations change?
Read a surface by its interruptions.
The ring study puts several visual textures close together: smooth curved metal, raised ornament and small recessed marks. Follow one highlight as it crosses those areas. The interruption often reveals the shape more clearly than the brightest point does.
The images were created as photorealistic digital artwork. Apparent scratches, inclusions and reflections are illustrative details. They should not be used to identify or assess a physical gemstone.
A boundary and two indices.
The light bench uses the relation n₁ sin θ₁ = n₂ sin θ₂. Both angles are measured from the normal: the line perpendicular to the boundary. Increasing the second index, with the first index and incoming angle fixed, reduces the refracted angle in this ideal model.
For example, an incoming angle of 40°, with indices 1.00 and 1.50, gives a refracted angle of approximately 25.37°. These are chosen model values, not readings from the jewellery images.
Assumptions
- One flat boundary and two uniform materials.
- Ray directions only; no intensity or energy calculation.
- No wavelength-dependent dispersion or absorption.
- No simulation of multiple gemstone facets or internal paths.
The diagram and controls are original. For the underlying physics, see OpenStax: The Law of Refraction.
Try the model ↗When the ray stays inside.
Total internal reflection can occur when light travels from the higher index to the lower one. The critical angle is calculated as arcsin(n₂ / n₁). Above that angle, the model hides the transmitted ray and draws the reflected direction.
With indices 1.50 and 1.00, the critical angle is approximately 41.81°. Choose the “Internal reflection” preset to see an incoming angle of 60° exceed that threshold.
Read more in OpenStax: Total Internal Reflection. The lab is a simplified educational tool, not an instrument for gemstone grading or optical design.
Keep an observation
The download button records the angle, both indices, the calculated result and the model state. It saves a JSON file locally. No account is needed, and no settings are sent to a server.