Revealing Hidden Light
Happy June and welcome to summer! It is the time of year when people start talking about blocking the sun’s UV waves and appreciating the vibrant colors of plants and flowers blooming everywhere. What do UV waves and colors have in common? They are both forms of light. Let’s dive in for a deeper look.
At its most basic level, light waves are part of the electromagnetic spectrum. The electromagnetic spectrum is a way of organizing light based on how long the waves are. Wavelengths are measured in either nanometers (one nanometer is only 0.000000001 meters long), meters, or kilometers depending on which type of light wave you are referring to. And there are many different types of light out there! On the shorter end of the spectrum are tiny gamma rays measuring only 0.01 nm, while radio waves on the opposite end can stretch up to 100 km long!. The sun’s UV waves range from 100 to 400 nm and right next to those UV waves is visible light, the only part we can see, with wavelengths ranging from 380 nm to 750 nm. The electromagnetic spectrum covers a huge range of distances and most of this light is invisible to us! Think about that for a moment. There is a ton of light that we cannot see, moving all around us all the time!
The range of visible light waves look white when you look at all of the wavelengths mixed together. You don’t see colors until you go deeper into the visible part of the spectrum. The colors appear when you further divide the 380 nm to 750 nm into smaller bands. True violet light is seen at 400 nm, blue is 475 nm, green is 555 nm, yellow is 580 nm, orange is 610 nm, and red is 650 nm.
Science With Depth Practice: One Phenomenon, Multiple Paths
The Science With Depth philosophy of using one phenomenon to create multiple learning paths will show you how to take a universal phenomenon like a rainbow and transform it into a multi-tiered learning experience for your students. Read on to learn how to break open the electromagnetic spectrum so every student can discover what is hidden inside.
Materials:
Diffraction gratings (500 lines/mm or 1000 lines/mm are both fine for this activity)
Light sources (fluorescent, LED, flashlight, indirect sunlight - remind students to never look directly at the sun!)
Color filters or colored cellophane
Steps:
Path 1 (DOK 1): The First Look (Identify & Document)
The Action: Hand students a diffraction grating. Instruct them to hold it up and look toward an indoor light source or indirect sunlight.
The Access Point: List the exact colors hidden inside the "white" light. Draw the color pattern precisely as it appears.
The Depth Insight: Students physically discover that white light is not a single entity, it is a collection of hidden colors.
Path 2 (DOK 2): Shifting the Source (Compare & Infer)
The Action: Provide a variety of light sources (an old incandescent bulb, a modern LED, and a fluorescent tube). Instruct students to analyze each source through their grating.
The Access Point: Compare the resulting color bands. Does the order of the colors change when the source changes? Why or why not?
The Depth Insight: Students infer that while some light sources lack certain colors, the spatial order of the colors remains invariant.
Path 3 (DOK 3): The Wavelength Argument (Plan & Validate)
The Action: Introduce color filters. Instruct students to predict what will happen to the rainbow pattern if they place a red filter in front of the white light source.
The Access Point: Plan a brief test to prove that colors are organized strictly by their physical wavelength. Observe that the red light passes through and lands in the exact same spatial location it occupied when the light was white.
The Depth Insight: Students validate the argument that color is a direct measurement of the physical size of the wave itself.
Reflections from the Deep:
Here is a question to pose to your students, and to ponder yourself as you wind down this school year:
"The rainbow was always inside the white light, even when your eyes couldn't see it. What hidden strengths, bright moments, or unexpected lessons were inside your classroom this year that you couldn't see until you looked through a different lens?"
The NGSS Framework: Making Connections:
This practice goes deeper than memorizing the acronym ROY G BIV. Students learn the physics behind color through two powerful NGSS dimensions:
Crosscutting Concept: Patterns. Students track the repeating, predictable order of wavelengths of color via different light sources.
Science and Engineering Practice: Planning and Carrying Out Investigations. By manipulating variables (the light sources and filters), students transition from passive observers to active, data-driven scientists.
Benthic Buzz:
Have you ever tried asking your students if there are any colors hiding inside colored light? (The answers might surprise you!). What are your favorite, low-cost ways to create rainbows and chase light waves in your classroom? Drop your best "light hacks" and student responses in an email to me at holly@sciencewithdepth.com. Let’s pool our collective wisdom and get the community buzzing with bright ideas for next year!