I’ve seen plenty of weird computer bugs in my time, but nothing quite like what Peter Onion discovered in February 2015. He was proudly photographing his brand new Raspberry Pi 2 when something bizarre happened—every time his camera flash went off, his Pi instantly powered down.

At first, Peter thought it was just a coincidence. But after it happened three times in a row, he realized he’d stumbled onto something unprecedented. His post to the Raspberry Pi forums with the innocent title “Why is the PI2 camera-shy?” would soon reveal one of the strangest hardware vulnerabilities in modern computing history.

Peter Onion wasn’t just any user—he was a veteran of the Raspberry Pi community and a regular at Raspberry Jams in Cambridge and Bletchley. When he reported that taking flash photos caused his Pi 2 to crash, the community took notice.

What happened next was like watching a crowd-sourced CSI episode unfold in real time. Forum users immediately began experimenting with different cameras and light sources. User “jdb” made a crucial discovery: his Samsung Note2 with LED flash caused no problems, but his Samsung K Zoom with a xenon flash reliably crashed the Pi 2.

This distinction between LED and xenon technology became the first major clue. The community had found their smoking gun—but they still needed to figure out why.

The Hunt for the Vulnerable Component

The real detective work began when users started systematically testing which part of the Pi 2 was actually vulnerable. The initial assumption was that the main processor chip might be the culprit, but covering it with a blob of Blu-Tack (yes, really) didn’t solve the problem.

Then someone tried flipping the Pi upside down. Suddenly, it was immune to flash photography. This proved the vulnerability was purely optical—light had to physically reach a specific component on the board.

Through methodical testing, the community isolated the problem to the U16 chip—a small power supply regulator located between the USB connector and HDMI port. When they covered just this tiny component with Blu-Tack, the crashes stopped completely.

But what made this particular chip so sensitive to light?

The Physics Behind the “Xenon Death Flash”

The answer lay in modern semiconductor packaging. The U16 chip used something called Wafer-Level Chip Scale Packaging (WL-CSP), which is exactly what it sounds like—a bare silicon die with solder balls attached directly to the circuit board. Unlike traditional chips that are fully encapsulated in opaque plastic, WL-CSP chips prioritize miniaturization over protection.

This exposed silicon became the Pi 2’s Achilles’ heel. When hit by high-intensity light, the photoelectric effect kicked in—the same phenomenon Einstein won a Nobel Prize for explaining. High-energy photons striking the semiconductor created unexpected electron flows, disrupting the voltage regulation circuitry and causing an immediate shutdown.

The intensity threshold was crucial. Regular LED camera flashes didn’t produce enough photons, but xenon flashes and laser pointers packed sufficient punch to trigger the malfunction. Even more interesting, the effect required silicon’s specific bandgap energy—meaning infrared and visible light could potentially cause problems, but only at extreme intensities.

This Wasn’t Actually Unprecedented

While the Raspberry Pi incident captured headlines, similar optical interference problems had been lurking in the semiconductor industry for years. An engineer at EDN Network revealed that his company had encountered the exact same issue twelve years earlier with a CSP amplifier for a cell phone prototype. The phone’s own camera flash would cause the amplifier to spike when light penetrated the chip packaging.

Even more dramatic was a 1997 incident at the Haddam Neck nuclear plant in Connecticut. A training department member took a flash photograph of a fire detection panel, and the camera flash tricked an EPROM chip into thinking there was a fire. Within seconds, the Halon fire suppression system activated, forcing operators to abandon the control room for 35 minutes while the gas cleared.

These incidents revealed a broader truth: as semiconductors became smaller and more exposed, they also became more vulnerable to optical interference that traditional testing never considered.

The Fixes: From Blu-Tack to Better Design

The immediate solution was charmingly low-tech. The Raspberry Pi Foundation recommended covering the U16 chip with opaque materials—Blu-Tack, electrical tape, or even putty would do the trick. This worked because it blocked light from reaching the sensitive semiconductor while maintaining normal electrical operation.

But the real fix came with hardware revision 1.2 of the Pi 2, released later in 2015. Instead of just adding optical shielding, the Foundation implemented a completely different power management architecture using the BCM2837 system-on-chip (the same processor later used in the Pi 3). This eliminated the optical sensitivity entirely through better circuit design rather than band-aid solutions.

Testing confirmed that earlier Raspberry Pi models (A, B, A+, B+) had never been vulnerable to the “xenon death flash” effect, making this a uniquely Generation 2 problem that was both discovered and solved by the community.

What This Revealed About Modern Electronics

The Raspberry Pi 2 vulnerability highlighted a fundamental tension in modern electronics design. The relentless push toward smaller, cheaper components had introduced failure modes that traditional testing methodologies simply didn’t consider. Standard electromagnetic compatibility testing covers radio interference, but who thinks to test whether taking a photo will crash your computer?

The incident also demonstrated the hidden risks of chip-scale packaging. While WL-CSP technology enables the tiny, powerful devices we rely on today, it essentially puts bare silicon dies directly onto circuit boards with minimal protection. Cost and size benefits come at the expense of environmental robustness.

Most importantly, it showed how unconventional use cases could reveal vulnerabilities that lab testing missed. The specific combination of circumstances—a xenon flash camera pointed at an exposed power regulation chip—fell completely outside typical validation scenarios.

The Legacy of an “Adorable Bug”

The Raspberry Pi Foundation handled the incident with remarkable transparency, calling it “the most adorable bug we’ve ever come across” and turning it into a physics lesson about the photoelectric effect. This open approach contrasted sharply with typical corporate responses to hardware flaws and helped maintain community trust.

The vulnerability became a teaching tool in electronics courses, providing a tangible example of how fundamental physics principles affect real-world technology. Students could literally see the photoelectric effect in action by watching a computer crash when photographed.

More broadly, the incident contributed to increased industry awareness about optical interference in semiconductor design. While such specific vulnerabilities remain rare, the Pi 2 case demonstrated why comprehensive testing needs to consider increasingly unconventional attack vectors.

Lessons for Today’s Connected World

The Xenon Death Flash story feels almost quaint now—a simpler time when the biggest worry was whether taking a photo might crash your hobby computer. But it foreshadowed bigger concerns about hardware security and the unintended consequences of aggressive miniaturization.

Today’s devices pack even more functionality into even smaller packages, often using advanced packaging technologies that prioritize performance over protection. The Internet of Things has put embedded systems into every corner of our lives, many using similar cost-optimized designs that might harbor their own unexpected vulnerabilities.

The Pi 2 incident reminds us that the most interesting bugs often come from the intersection of unrelated technologies—in this case, photography and power regulation circuits. As our devices become more interconnected and our technology stack more complex, we should expect more such surprises.

The good news? When weird bugs do surface, communities like the Raspberry Pi forum show that collective problem-solving can be remarkably effective. Sometimes all it takes is enough people willing to stick Blu-Tack on circuit boards and see what happens.

And that’s probably the most important lesson of all: in a world of increasingly complex technology, a little curiosity and community collaboration can solve even the strangest problems.