Three White Lights - Physics Demonstrations - Three White Lights | Physics Undergraduate Labs

The incandescent bulb becomes extremely hot during operation and remains hot for several minutes after being turned off. Ensure adequate clearance from flammable materials, position the stand where it cannot be accidentally touched, and allow sufficient cooling time before handling. Do not leave the incandescent source on for extended periods when not actively demonstrating.

Purpose

Compares the spectra of three "white" light sources through diffraction gratings. Students see that incandescent light produces a continuous blackbody spectrum, the CFL shows discrete mercury emission lines, and the LED shows a sharp blue/violet peak plus broad phosphor emission.

$Light tower (right) with three vertically-mounted white light sources and their diffraction grating spectra (left): LED strip spectrum with horizontal line structure from strip segments (top), incandescent smooth continuous rainbow (middle), CFL discrete emission lines (bottom)$

Figure 1: Light tower (right) with LED strip (top), incandescent bulb (middle), and CFL (bottom). Their spectra through a diffraction grating appear at left: LED continuous with visible strip structure, incandescent smooth rainbow, CFL discrete emission lines.

Medium Diffraction Grating

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White Light Stack

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Safety Warnings

Warning: Heat Hazard from Incandescent Bulb

Purpose