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Imagine simply scanning a photograph with an app to determine whether a light or light fixture is dark skies friendly.
GLAS interns Sydney Simon and Olivia Boyd are working toward that.
“We’re going to evaluate light based on color temperature, luminous flux and light angle. We’re trying to determine the dark skies friendliness of certain light fixtures based on these three factors,” Sydney said in a late July presentation to staff and interns at GLAS Education.

Five people, three young women and two young men, around a table in a large room with a television screen in the right background. Sitting to the far left is a young woman with brown hair wearing in a light-colored blouse. Behind her is standing a young woman with her brown hair pulled back. She is wearing a light red jacket over a dark purple shirt and blue jeans. Standing to her right is a young woman with dark brown hair flowing over her shoulders, wearing a black dress, her hands elevated as she talks. In the foreground are two young men facing away from the camera. A graphic is projected on the television screen.
Summer 2023 GLAS interns Olivia Boyd, standing left, and Sydney Simon, standing right, explain their project to use photographs to evaluate dark skies friendly light based on color temperature, luminous flux and light angle. The two University of Chicago astrophysics students spent weeks working on computer code and programs to accomplish their goal.

The two University of Chicago astrophysics students are working on complimentary Python programs that can determine the luminous flux, color and light angle of fixtures and source.
While the envisioned process sounds easy, getting there is proving to be complicated. That’s because while a photograph might look like a representation of reality, it isn’t. What appears in a photo depends on the ambient light, whether that light was filtered, the angle of the lens and the speed of the shutter.
The students are working out ways around those problems.
Sydney is working on a program to determine the angle of light from a fixture.
The problem she has been solving is that light angles could be misrepresented by photos not taken straight on. Her app takes in night images of a light fixture (with the light on), and proceeds to filter out all parts of the image that aren’t in the image’s max intensity range. After applying the filter, her program applies an edge detection algorithm called “Canny,” which returns the filtered image with only the edges/lines left. Her program then applies a line detection algorithm called “Hough,” which filters out shorter lines that are unimportant to the image. The program then averages the angles of the lines detected with respect to the vertical axis. The averaging process helps cancel out the effects of a photo taken at a crooked angle.
Olivia is working on luminous flux and color temperature.
“I’m still working on the former. I am on the third iteration”, Olivia said.
“The color temperature program was a much easier project,” she said.Olivia explained that the color of a light is a function of its temperature [units: Kelvin (K)]. In short, the higher the Kelvin rating, the bluer the light. A light at 2000K (2,000 Kelvin) appears reddish-yellow. A light at 8000K appears bluish white. Using code she’s put together, Olivia said she can convert the RGB color streams to Kelvin ratings.

Graphic of nine light fixtures showing the relative temperatures of light from red-yellow to bright blue-white using the Kelvin scale. The graphic is titled Lighting Temperature Guide.
Light temperature, from reds and yellows to bright blues using the Kelvin scale. Lower Kelvin scores are more dark skies friendly.

“It is pretty simple. Basically, it (the program) considers the RGB color streams among some other more nuanced factors.” Olivia said. R-G-B stands for red, green and blue– the three colors that usually make up the 24 bit pixels many images are made of. “It works well. The only thing I am trying to refine is its accuracy, which operates in a range of 600K. But, I’m not even sure if the range is that vast, because I have doubts that some of the lights in the images I ran were true to their color temperature labels”, Olivia said. Still, considering that color temperature is on a scale of 8000K, that margin of error isn’t terrible– around 7.5 percent. And, it is definitely good enough to give people a good indication of whether their light color is dark sky friendly.
Olivia is also experimenting with ways to determine light luminous flux through photos.
The differentiating aspects of the three iterations are as follows:

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