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Investigation 3 – PreLab









Forensic scientists use black lights to analyze crime scenes. To pick out fingerprints, for example, they often dust with fluorescent dye under a black light. This makes it easier to pick the fingerprints out from surrounding dirt.


This Investigation is designed to help you to answer the following Focus Question:

  • How does wavelength affect the perception of light?

Note: This question is located in your SDR at the beginning and end of the Investigation.



As a class, read the Background(s) in the Investigation. When finished, discuss the following concepts as a class:

  • An absorbance spectrum shows how different wavelengths of light are absorbed by a substance.
  • Some transparent materials, such as clear window glass, are transparent to all wavelengths of visible light.
  • Other transparent materials are transparent to only certain wavelengths of visible light. For example, the red glass of a traffic light appears red because the pigments in the glass absorb all the wavelengths of visible light except those around 700 nm (red). This wavelength is transmitted and you see red light.
  • Wavelengths of light are absorbed and reflected by different colored opaque objects.
  • This concept can be easily demonstrated using filters. Each filter only allows a particular wavelength of light to pass through it. The color of the filter indicates the wavelength that passes through it. For example, the red filter only permits red wavelengths of light to pass through it, not green or blue wavelengths of light.

Note: These concepts are integrated into the Background(s) and are used to deepen students’ comprehension of the big ideas.


The following list includes Key Terms that are introduced in the Investigation Background(s). They should be used, as appropriate, by teachers and students during everyday classroom discourse.

  • transparent
  • opaque

Note: Definitions of these terms can be found on the Introduction page to the CELL.

Note: Additional words may be bolded within the Background(s). These words are not Key Terms and are strictly emphasized for exposure at this time.


  • Complete the Recall section in your SDR.
    • Can you tell when light wavelengths will be absorbed or transmitted by objects?
    • What kind of objects absorb light?
    • What kinds of objects transmit light?
  • During this Investigation, you will investigate the relationship between light and the color of transparent substances.
  • Play the video below. Remember to follow along with your SDR and make any notes that you think might be helpful in the lab.
  • After the video, divide into your lab groups to discuss strategy for the lab. For example, you may assign certain group members to perform specific functions during the lab.

Note: The purpose of the video is to allow you to anticipate the laboratory experience you will soon encounter. You should leave this PreLab session with a firm idea of what to expect and how to perform in the lab.

Note: Homework is posted below the video.


You should review the Investigation and video in preparation for the Lab.