Can sunlight passing through a prism start a fire?

Dear Cecil:

I bought some crystal prisms at a crafts fair and was going to hang them in a window on the west side of my house. Then I got to thinking about an experiment we did in school, which consisted of having sunlight go through a magnifying glass onto paper. The paper started to smolder. Now I'm worried that if I hang the prisms in the window, I may come home to a smoldering heap of charred wood. At a shop that sells crystal prisms, I asked about the likelihood of this happening. The shop owner assured me sunlight coming through a prism would not start a fire, even if it hit a stack of newspapers. But I figured, of course he would say that, he sells prisms. So I turn to you, Cecil. Do I have anything to worry about?

Cecil replies:

Relax. Magnifying glasses concentrate light, prisms scatter light. That’s why you see those bands of color — the prism has caused the different wavelengths of the light to separate. Interesting, yes; dangerous, no.

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