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Redirected Sun: Same Light or New Light?

March 4, 2013

In inquiry, many groups today wanted to say that every point on an object (like a tree) acts like its own source of light. And they wanted to call each point on the tree a secondary source of light, because objects like trees only act like sources of light when there is a primary source of light (like the sun) shining on it. One group talked about this being like a food chain. Plankton is a primary food source, but things that eat the plankton become food for other things. We don’t say that only plankton is food, because everything in the food chain is food for something else. And so with light, everything that sunlight hits becomes a source of light itself. The secondary sources of light need primary sources, just like links up the food chain need primary sources.

Others in class didn’t really like the idea of calling objects like trees sources of light, even if we acknowledge their secondary nature. One argument is that objects like trees are not sources of light; because they merely act as obstructions that can redirect the light. They don’t produce and source out any light. Many in this camp would, however, be OK with saying that objects like glow in the dark stickers can be sources of light, because they can glow on their own, even once the primary source is taken away.

A wedge point became whether or not the light coming off objects was the same light or not, and if it is the same or different, what exactly is the same or different.

Some of the ideas that emerged were the following:

When sunlight comes upon an object like a point on a tree, the light that comes off the tree is

  • Essentially the same light that came from the sun, simply redirected along new paths. The light that comes to the tree and off the tree is just light. Light is light is light. 
  • New light altogether, because the “sun light” was first absorbed and then different “tree light” came off. The “tree light”is the color of the tree, not the sun. 
  • The same light that came with the sun, but now with something more it picked up from the tree. The sunlight is now green, because it now carries the tree color with it.
  • The same light but filtered–in the process of hitting the tree, some of light from sun was absorbed and some of the light was redirected. The green light is redirected, but other light is used for photosynthesis.
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2 Comments leave one →
  1. ljatkins permalink
    March 4, 2013 9:06 pm

    Genius! – Friday my students identified three different ideas about cyan: (1) cyan pigment contains green and blue things that then reflect g&b light. (2) cyan itself reflects green and blue light. (3) cyan reflects the kind of light that activates the G&B cones. I tried to go bananas for this — delineating these ideas and recognizing them as three different ideas is to have accomplished something really significant. I don’t care if we don’t figure out which it is.

    • March 4, 2013 10:35 pm

      Right, the work is in carving out the ideas with sufficient precision such they become ideas, and the answer seems less important. I’m still thinking through what I think exactly. The few people who disliked the idea of calling them sources of light were really important in pushing the other people to clarify their idea. I’ve been saying that such people are playing the role of “holdouts”, and I keep talking about the value of having people who play that role.

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