The Public Laboratory for Open Technology and Science (PLOTS) has developed an inexpensive, DIY “thermal flashlight” that you can build into an old VHS tape case. Paired with a camera, the device lets you create a color heatmap of interior surfaces. This post on the PBS Idea Lab blog describes the early history of the tool’s development. And now a school program in Harlem, New York is planning to use the device to document apartments that require better insulation.

Here’s how to make one. The thermal flashlight uses a $14 non-contact infrared thermometer that reads temperatures from short distances. It translates the readings into colored light that shines back onto the test surface from an RGB LED: blue for cold and red for hot. To make a heatmap, you take a long-exposure photograph in the dark as you sweep the flashlight over all of the surfaces you want to image. For best results, wear dark clothing, and of course stay out of the way of the camera’s view of the RGB LED light.

From New Scientist, photo: Jeff Warren.

Paul Spinrad

Paul Spinrad

Paul Spinrad is a broad-spectrum enthusiast, writer, maker, and dad who lives in San Francisco. He hatches schemes at

  • iaDF!
  • Sara Wylie

    Thanks very much for your coverage of Public Lab’s work. This post needs some important corrections however to improve its accuracy. First, Public Lab is an open source research and development community, it is therefore improper to say to that I, Sara Wylie, developed this technology. In fact there have been a wide array of people involved in developing and conceptualizing this tool. This PBS blog from Public Lab describes the early history of the tool’s development: I would very much appreciate a correction to your blog to address this misattribution. If you would instead attribute the tool’s development to the Public Lab community broadly and direct readers to the Public Lab page for the Thermal Flashlight:, that would be great.

    Second, the Harlem School Project has not yet happened, so it is improper to say they are currently using the device. If you could make that correction it would be much appreciated.

    Thanks again for your interest and coverage of Public Lab’s work.

    Sara Wylie
    Director of Toxics and Health Research
    Public Laboratory for Open Technology and Science

    • Paul Spinrad

      Thank you for the corrections, Sara– I just made them and also linked to that writeup on the PBS Idea Lab blog. Great project, great work!

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  • Thermal Insulation Calculation

    Thank you so much for your blog and your coverage of Public Lab work i hope you give me more deeply knowledge about Thermal Insulation Calculation..