Photometry Topic

Luminosity

Concept 1 demo

Cuda I-150 fiber optic light source on left, small square barrier on a clamp mounted on an optical rail, green gridded chalkboard in background — barrier at maximum distance, no visible shadow

Inverse Square Law

A point light source casts the shadow of a small square barrier onto a gridded board. Each time the barrier-to-source distance is halved, the shadow area quadruples — directly visualizing …

Blackbodies

Concept 2 demos

Two cardboard boxes of different sizes with dark paper roofs and white block "chimneys," each with a black paper panel on the front containing a circular aperture that appears identically black

Blackbody Boxes

Two boxes with different interior colors (white vs. black) show identical black apertures when closed, demonstrating that a cavity with a small opening approximates an ideal blackbody regardless of interior …

Red, green, and blue square glass filters mounted vertically in lens holders on a ring stand, all brightly illuminated by an incandescent bulb behind them at full power

Color and Temperature

Shows how a blackbody spectrum shifts with temperature by varying the voltage to an incandescent bulb viewed through red, green, and blue filters. As voltage decreases, blue disappears first, then …