Let the light shine in

January 12, 2021
A photo compilation of students holding up their homemade spectrometers

This fall, PS10 students couldn’t go to lab, so they made one at home

By Caitlin McDermott-Murphy


This fall, undergraduate students in Physical Sciences 10 (PS10) got a big package in the mail. Some opened it in a dorm room; others tore into the cardboard in kitchens and bedrooms across the world (one package flew across the pond to a European kitchen). They pulled out: more cardboard—laser cut into a puzzle of rectangles—wires, and multicolored LED light bulbs in the shape of tiny mushroom caps.

“Don’t worry about breaking the cardboard,” said Alvin Hsu, a Ph.D. candidate in the Graduate School of Arts and Sciences and head teaching fellow for PS10. In an instructional video for students, Hsu guided Lu Wang, a preceptor in chemistry, how to punch one of those LEDs through a cardboard slat. She pushed harder and the light popped through.


A screenshot of Hsu pointing to a schematic with different sized cardboard rectangles next to it

A screenshot of Alvin Hsu demonstrating how to construct a homemade spectrometer from cardboard

In a PS10 instructional video, Alvin Hsu (whose hands can be seen in the photos above,) instructs Lu Wang how to build pre-cut cardboard slats into a homemade spectrometer. Image courtesy of Alvin Hsu/Lu Wang


For centuries, chemists could stroll down to their local pharmacy (“the chemist”) to pick up all they needed to perform experiments at home. For safety, most chemistry is now confined to sterile labs. There’s another reason: Modern equipment, like thousand-dollar spectrometers, is expensive. In previous years, PS10 students spent hours in the laboratory, but this year, with labs either closed or operating at low capacity during the coronavirus pandemic, they got to experience how chemistry used to be done.

“For centuries, people did labs basically in their kitchens and didn’t have fancy equipment,” said Adam Cohen, the course’s head instructor and a professor of chemistry and of physics. So, to study how light interacts with matter, the students connected their cardboard rectangles, wove wires into a breadboard, hooked up an Arduino (a tool to read electronic signals) and presto: They each owned their own spectrometer for just about $50 and an hour and a half of their time.

Over the summer, when an in-person semester seemed less and less likely, Hsu scrambled to invent a build-it-yourself spectrometer “kit.” He cut cardboard with a razor blade, tinkered with the circuitry, and designed code. He built dozens of prototypes, which, Hsu said, are “starting to take up way too much room in my tiny apartment.”

In October, when PS10 students constructed Hsu’s final spectrometer design, their toaster-sized instruments fit easily on a desk or counter. After guiding students through the build (and adding office hours to handle snags in the circuity or code), the teaching crew led them through a series of hand-on labs to analyze how colored lights interact with colored water. With just water, food coloring, light, and their new spectrometer, they could see, touch, and analyze a very complex concept: the quantum nature of light.

In one lab, for example, students brewed a batch of sapphire blue butterfly pea flower tea. When they added acid—lemon or vinegar—their solution morphed into a fluorescent purple. With their spectrometer, they could analyze exactly how acid forces this color shift: “Seeing it in person,” said Benjamin Tang, a freshman in PS10 who lived at home in Atlanta, Georgia for his first Harvard semester, “I don't know, just changed how I thought about it. It's not just some theory on paper.”

That was one of Wang’s goals (“So they’ll see that chemistry is everywhere,” she said.) and Cohen’s, too: “What we're doing now is far more interesting and engaging for the students than what we had ever done in the past,” he said, “because it's not served on a silver platter and it's much more of an adventure.”

Ariel Wang (’23), a freshman who plans to concentrate in mechanical engineering, said of all her courses, PS10 changed the most to accommodate for remote learning. She was surprised and delighted at how hands-on the curriculum ended up. “I guess it satisfies the engineering interest in me,” she said. She most enjoyed constructing her spectrometer, which, she said, “was surprisingly accurate.”


A screenshot of a Zoom conference with students holding up their homemade spectrometers

A screenshot of a Zoom conference with students holding up their homemade spectrometers

A screenshot of a Zoom conference with students holding up their homemade spectrometers

Alvin Hsu (top left) and Lu Wang (in all three Zoom conference screenshots), get a glimpse of the homemade spectrometers made by their PS10 students. Photos courtesty of Lu Wang 


In an ironic shift, PS10 teaching staff also changed the course’s final project. In previous years, when students could access the lab, most took a theoretical approach to a topic like solar cells, steam engines, or batteries. This year, they could choose an experimental approach instead.

For example, Jeremy Rasmussen, a freshman who plans to major in chemistry with a minor in politics, chose to upgrade his spectrometer to detect infrared light, which can sense the radiation emanating from warm objects and measure their temperature. Rasmussen is pleased he gets to keep the device after the course ends, so he can tinker with more upgrades at home.

Other students plan to use their spectrometers to measure the temperature of the sun by analyzing its spectrum of light. Another will tap a seltzer bottle to measure how carbon dioxide gas absorbs infrared light, an experiment that mimics the greenhouse effect in the Earth’s atmosphere.

But Brayant Garcia, a sophomore concentrating in physics and chemistry, plans to stay in the theoretical realm to study the precarious balance necessary for efficient (and non-explosive) nuclear fission reactions. At the same time, during the January break, he plans to volunteer with local middle schools to help even younger students build their own do-it-yourself launcher—the same hands-on experiment that attracted him to study science.

Garcia said he learned just as much in a virtual PS10 than he did in previous on-campus courses. But one component—wet labs with volatile chemicals—was still too dangerous to replicate at home. (The students did perform one wet lab, which required a lab safety component. Each student, said Rasmussen, had to “submit a selfie of yourself in full lab gear: long sleeve shirt, long pants, closed-toe shoes, gloves, goggles” before they could dissolve their copper nitrate into salt water).

So, Garcia is eager to return to campus and use a real spectrometer.

“When they use a real one,” said Cohen, “they’ll actually know what’s going on under the hood.”