Christmas Lights: Series vs Parallel Circuits (3D)

Wiring

Click any bulb in the 3D scene to burn it out (or repair it). Drag to orbit, scroll to zoom.

Circuit Parameters

Number of bulbs N 8

Source voltage V_s 12.0 V

Bulb resistance R 20 Ω

Live Circuit Readouts

Total resistance

160.0 Ω

Total current

75.0 mA

V per bulb

1.50 V

Total power

0.90 W

The real physics

Each bulb is modeled as an ohmic resistor of resistance R. In series, every bulb shares the one and only current path, so the same current I flows through all of them: I = V_s / (N·R), and each bulb's share of the source voltage is V_s/N — Kirchhoff's voltage law divides the loop's total EMF across N equal drops. Break or burn out any single bulb and the loop opens: I = 0 everywhere, and every bulb goes dark, not just the burnt one.

In parallel, each bulb is its own branch directly across the source, so by Kirchhoff's voltage law every active bulb sees the full V_s, independent of how many other bulbs are present. Burning one out just removes its branch — Kirchhoff's current law still balances for the rest, whose currents (I = V_s/R each) and brightness are completely unaffected. Total current is the sum of the active branches' currents, so total resistance actually drops as more bulbs are added in parallel.

Series:   R_tot = N·R        I = Vs/R_tot        V_bulb = Vs/N        P_bulb = I²R
Parallel: R_tot = R/N_active  I_bulb = Vs/R        V_bulb = Vs          P_bulb = Vs²/R

Brightness of each bulb is rendered from its own computed power P (via emissive intensity and point-light output), so a dimmer bulb in series with a large N visibly glows weaker than a bright single parallel bulb at the same source voltage — the real, measurable trade-off between the two wiring schemes.

Lit bulb (brightness ∝ power) Burnt-out / dark bulb

Click a bulb to burn it out / repair it

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