Chapter 25, Problem 59RPP

Incandescent lightbulbs—soon to disappear Australia, Canada, New Zealand, and the European Union started phasing out incandescent lightbulbs in 2009. The United States phased them out in 2014. These bulbs have provided light for the world for more than 90. years What’s the problem?

Incandescent lightbulbs produce light when electrons (electric current) move through the filament and collide with tungsten atoms and ions in the filament, causing them to vibrate violently. Accelerating charged particles emit electromagnetic radiation. This is true for vibrating and accelerating particles in the filament, in your skin, and on the Sun. The $\text{35 °C}$ skin of a person emits most of its radiation in the low-frequency long-wavelength infrared— sometimes called thermal radiation. At $\text{2500 °C}$, the filament of an incandescent lightbulb emits most of its radiation as higher frequency infrared radiation and just $10\%$ as visible light (very inefficient if the goal is to produce light). At $\text{6000 °C}$, the Sun emits about $45\%$ in the infrared range and $40\%$ in the visible light range.

Banning incandescent bulbs will reduce energy usage. According to the Department of Energy, about ${\text{10}}^{\text{18}}\text{J}$ of electric energy is used each year in the United States for household lighting. Compact fluorescent lightbulbs (CFLs) and light-emitting diode (LED) bulbs use about one-fourth the energy of incandescent bulbs. Switching to CFLs and LEDs would also reduce greenhouse gas emissions by reducing the need for power produced by coal-burning electric power plants.

How much money will you save on your electric bill each year if you replace five 100-W incandescent bulbs with five CFL or LED 25-W bulbs that produce the same amount of light? Assume that the bulbs are on $\text{3}\text{.0 h/day}$ and that electric energy costs $\text{\$0}\text{.12/kW}\cdot \text{h}$.

a. $5

b. $10

c. $20

d. $50

e. $100