Why does a sodium vapor street light appear yellow instead of white?

• A. Because sodium vapor produces a continuous spectrum that is strongest in the yellow region.
• B. Because the lamp uses a yellow filter to block other colors of light.
• C. Because sodium atoms emit light primarily at specific wavelengths in the yellow region of the visible spectrum.
• D. Because the sodium vapor absorbs all colors except yellow from the surrounding environment.

Answer: (C)

Verified step by step guidance

1. Understand that the color emitted by a light source depends on the wavelengths of light it produces or emits.
2. Recognize that sodium vapor lamps work by exciting sodium atoms, which then emit light as their electrons return to lower energy levels.
3. Recall that sodium atoms emit light at very specific wavelengths, primarily the bright yellow lines known as the sodium D-lines, around 589 nm in the visible spectrum.
4. Note that this emission is not a continuous spectrum (which contains all visible wavelengths), but rather a line spectrum with strong intensity in the yellow region.
5. Therefore, the sodium vapor street light appears yellow because it emits light mainly at these specific yellow wavelengths, rather than producing white light that contains all colors.