Series and Parallel Light Bulbs

This demonstration uses 120V AC mains power, which presents a serious shock hazard. The voltage is sufficient to cause injury or death. All wiring must be completed with the power cable unplugged. Never rewire circuits while plugged in. Ensure all connections are properly insulated and secure before plugging in. Only qualified personnel should assemble or modify the circuits.

Accidentally creating a short circuit (direct connection between hot and neutral) will cause the circuit breaker to trip and may melt wire insulation, wire nuts, or socket terminals. Before plugging in each circuit, carefully trace all connections to verify proper topology. Use the continuity test function on a multimeter to verify correct wiring when unplugged.

Incandescent bulbs become extremely hot during operation (filament temperature ~2500°C, glass surface ~200°C). Allow bulbs to cool for several minutes before handling. Do not touch bulbs immediately after turning off power. When demonstrating, position bulbs away from flammable materials.

Purpose

Identical 60W bulbs wired in series vs. parallel show a dramatic brightness difference, making voltage division and power distribution immediately visible. Use handheld DVMs to measure voltage and current at various points in each circuit.

Four 60W globe-style incandescent bulbs in ceramic sockets on clear acrylic bases with binding posts. The two on the left glow bright white (parallel), the two on the right glow dim orange (series).

Figure 1: Two 60W bulbs in parallel (left, bright) vs. two in series (right, dim). Each bulb is mounted in a ceramic socket on an acrylic base with binding posts for flexible wiring.

Danger: High Voltage AC Hazard

Warning: Short Circuit Prevention

Warning: Hot Bulb Warning

Purpose

Safety Warnings

Danger: High Voltage AC Hazard

Warning: Short Circuit Prevention

Warning: Hot Bulb Warning

Purpose