In an ordinary household lamp, what are the percentages of light and heat?

• A. 5 percent light, 95 percent heat
• B. 20 percent light, 80 percent heat
• C. 15 percent light, 85 percent heat
• D. 10 percent light, 90 percent heat

Answer: (D)

Energy conversion efficiency in a typical incandescent lamp is such that most electrical energy is turned into heat rather than visible light. The filament, acting like a resistor, heats up and radiates energy, and only a small portion emerges as light. For a standard household lamp, about 10 percent of the power becomes light and around 90 percent becomes heat. That’s why a regular lamp gets hot while lighting up, and this distribution aligns with the option stating 10 percent light and 90 percent heat.