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Light Grapher

Welcome to Light Grapher!

LightGrapher is a Flash applet that turns your webcam or built-in computer camera into a rudimentary light sensor to display graphically the brightness of a model star (a lightbulb or even light-colored ball). When a [darker-colored] planet passes in front of the star, the brightness drops and a dip in the graph occurs. The software receives real-time data from the external webcam or internal computer camera. It may be run either directly from this page or downloaded and run locally in your browser.

  1. Set up planet(s) to orbit the model star (light bulb or white sphere).
  2. Start the software and click on "Allow" to let brightness data to come in from the camera.
  3. Aim the camera at the model star and center the targeting circle on the model star in the camera view.
  4. Alter the height of the camera/laptop or the star-planet model so that the planet(s) actually pass in front of the star as seen by the camera view. [The camera must be in the planets' orbit plane.]
  5. Set the size of target circle to fit the star using slider on right of screen. Making the targeting circle slightly smaller than the star is better than having it slightly larger than the star.
  6. If desired, change duration of "Capture Data" (default time = 30 seconds)
  7. Click "Capture Data" button and make planet(s) orbit.
  8. To adjust vertical scale, either click "Autoscale" or manually enter minimum and maximum % values at bottom and top of y-axis.
  9. You may click Pause button, then Resume, anytime during Data Capture.
  10. You can "Save" the data for any trial as a .png graphics file that you can open in a graphics program.
Click on this image to
Run LightGrapher:

LightGrapher icon large-- image of light bulb


Download LightGrapher a Flash file that can be opened locally with any Flash-enabled browser. Download and use the "Open" command in your browser.

Version 3.0, released 2012 Sep 14, is a major upgrade that

  • allows for use in rooms with ambient (non-dark) light, as in most classrooms,
  • works with either a light bulb as model star or simply a light colored ball,
  • has improved targeting control with a wider ranging slider to define target (star) size,
  • is not affected by background movements,
  • runs reliably every time.


  • It's best not to move the camera during a trial.
  • This software works best with
    - a light bulb as the model star at a distance of 1 meter or less, or
    - an opaque light-colored (or white) sphere as the star at a distance of 60 cm or less.

    In truth, the closer the model is to the camera, the better, but be sure to point out to students that the model represents a situation where the camera/spacecraft is light-years away from the star.
  • In general, slower cranking and larger target sizes gives better results.
  • In darker environments, the webcam requires more exposure time for each frame effectively decreasing the frame rate, so crank the orrery more slowly if surroundings are dark.
  • If the environment is dark, using a light bulb as model star is preferable to a white sphere.
  • If Autoscale is used, it may be necessary to reset Min and Max values on the vertical scale manually before a new trial, if lighting conditions change.

This software is © 2011 (version 1) and © 2012 (versions 2.0 and 3.0) by the Regents of the University of California. As a product of the NASA Kepler mission Education team, it may be used freely without charge.

This graphing software is designed to produce light curves for planet transit models, including:

Lightgrapher used in the
Telescopes to Tanzania campaign.

Photo of students in Tanzania with Chuck Ruehle all looking at computer monitor
Chuck Ruehle demonstrates to Tanzanian students how to use the "LightGrapher" program to learn about planet transits and the search for ExoPlanets. The interactive program, from NASA's Kepler Space Telescope site, provides a hands on teaching tool for students. Photo by Susan Ruehle.