How can spectra tell us what things are made of?

Stars and planets are too far away for a human to touch, yet we know what they are made of. Spectra make this possible! Let’s investigate how.

Atomic Emission Part 1: Incandescent vs. Metal Halide Bulbs

In Module 4, we explored thermal emission—light given off by all objects due to their temperature.

Now let’s consider a different kind of light emission by looking at the spectra of two types of light bulbs.

Spectrum Tool. Compare the spectra of the two light bulbs shown.

Spectrum Notebook. Answer these questions in your Notebook.

  1. Both these types of bulbs emit light in the visible part of the spectrum and can be used to light up a room. What are the key differences you observe in the bulbs’ spectra?
  2. Infrared radiation that is emitted by a lightbulb cannot be seen with our eyes, but still requires electricity to be produced. Based on the two spectra, which bulb is preferable for the environment? Explain why.
Source 1:
Lamps — Incandescent Bulb
Brightness
Full-intensity spectrum backgroundTransparency increases or decreases based on chart intensity, hiding or revealing the background
Left axis ticks
Spectrum intensity vs wavelength chart
Bottom axis ticks
Wavelength (microns)
Source 2:
Lamps — Metal Halide Bulb
Brightness
Full-intensity spectrum backgroundTransparency increases or decreases based on chart intensity, hiding or revealing the background
Left axis ticks
Spectrum intensity vs wavelength chart
Bottom axis ticks
Wavelength (microns)
part 2