What You Never Knew About Vault Lights

I recently had the chance to spend sometime visiting Seattle, Washington with my family, and as a historic preservation buff I was of course drawn to the original stories of the city and its early days. But let’s go back a bit, this trip actually started in Astoria, Oregon at a conference with a bunch of Window Restoration weirdos like myself.

While wandering around Astoria to visit the Goonies house and some other local landmarks, I noticed some unique rectangles of glass in the sidewalks. Not having a clue what this was I asked some of the locals and they told me about the underground spaces in Astoria and how these little purple pieces of glass provided illumination to the basements of buildings.

Now back to Seattle where when I saw the same thing to a much grander scale, I knew I had to learn more about it. Why were these little pieces of glass bed into concrete? Did they actually provide enough light to get anything done in the basement? Was I gonna fall through these century old sidewalk skylights? I had no idea and I absolutely had to know more.

What Are Vault Lights?

It turns out that once upon a time—before LED lights, before Edison’s bulbs, before the 9-to-5 soul-crushing glow of fluorescent office hell—people got creative with how they lit up underground spaces. Enter vault lights (or pavement lights if you’re British and fancy). These were the OG skylights, built right into sidewalks, providing natural light to basements, subterranean storefronts, subways, and speakeasies alike. Similar to a laylight, but for heavy foot traffic.

Today, they’re rare, mysterious, and often mistaken for some kind of weird sidewalk art. But vault lights have a history that’s as rich as the deep purple hue they developed over time. Let’s break down their past, present, and why they might just be the coolest architectural feature you didn’t know existed.

The Origin Story of Vault Lights

Our story begins in the 19th century, when underground businesses—like bakeries, workshops, and, let’s be honest, a few brothels—needed light but didn’t want to rely on whale oil lamps or early, highly flammable gas lighting.

Enter Thaddeus Hyatt, an American inventor who, in 1845, patented an innovative system of prismatic glass embedded into cast iron or concrete panels. Hyatt’s design allowed natural light to flood below ground, reducing the need for candles and gas lamp fumes underground, while also keeping the street intact for pedestrians and, later, horse-drawn carriages.

Not to be outdone, the Brits adopted and adapted the idea, where they became known as pavement lights. By the late 1800s and early 1900s, major cities across the US and UK had sidewalks that doubled as illuminated ceilings for underground commerce.

The Rise and Fall of the Vault Light

Vault lights had their moment in the sun (or, more accurately, under the sun) from the mid-1800s to the early 20th century. They became a staple in cities like New York, Chicago, London, San Francisco, and as is the case of my story, Seattle. Next week be sure to come back here to find out some of the coolest history of Seattle and how a hidden underground network of buildings and tunnels was formed (and lit with vault lights.

Back to the vault lights. But by the mid-1900s, they started fading into obscurity. Why? A few reasons:

• Electricity took over – Once electric lighting became widespread and reliable, the demand for passive daylighting systems like vault lights tanked.
• Maintenance was a nightmare – Over time, the iron or concrete frames would crack, and the glass would break or cloud over, making repairs costly.
• Modern building codes weren’t kind – Cities started prioritizing reinforced sidewalks and accessibility over charming-but-fragile architectural relics.

Eventually, many of these beauties were either removed or covered over, forgotten beneath layers of concrete and asphalt. When they were in use it was incredible the amount of light they could produce. Stranding beneath the Seattle streets when our tour guide turned off the lights the room was incredibly well-lit with only the very beat up and purple vault lights above our heads.

Why Were Vault Lights Purple?

If you’ve ever walked past an old set of vault lights and noticed they have a purple tint, congratulations—you’ve witnessed chemistry at work.

Originally, these glass blocks were clear or had a slight blue tint. But the glass used in the 19th and early 20th centuries contained manganese, which was used as a clarifying agent to remove the greenish hue caused by iron impurities. When exposed to UV light over time (years that is), the manganese oxidized, creating a beautiful (if unintended) purple or amethyst hue. Pretty beautiful mistake if your ask me!

So, basically, these things are like vintage wine—the older they get, the better they look.

The Good, The Bad, The Ugly

The Good:

✅ Natural daylighting: These were the original “green energy” solution, cutting down on the need for artificial lighting.
✅ Incredibly strong: Cast iron and reinforced concrete panels could support heavy pedestrian traffic and even early automobiles.
✅ Historically significant: They’re a major architectural and urban design relic from the Industrial Revolution.

The Not-So-Good:

❌ Slippery when wet: Old glass + rain = banana peel levels of disaster.
❌ Brittle with age: Years of wear, weathering, and improper maintenance can lead to cracking and breakage.
❌ Difficult to replace: Finding authentic replacements is a challenge (though not impossible—more on that below).

Are They Dangerous?

Not really—at least, not inherently. However, older and poorly maintained vault lights can become hazardous if the glass cracks or the metal framing starts corroding. In some cities, broken vault lights have been covered with metal plates, effectively erasing them from sight.

How to Date Vault Lights Like a Pro

This isn’t a lesson on making dinner plans for Friday night, but rather a fact finding mission to know if you’re looking the real McCoy. If you’re lucky enough to stumble across a set of intact vault lights, here’s how you can estimate their age:

• Pre-1900s – Typically smaller glass lenses, often clear or slightly blue-tinted. These are rare and were often custom-made.
• 1900s-1920s – Glass lenses become larger, and manganese-containing glass starts showing purple discoloration over time.
• 1930s-1950s – Less common as electricity takes over, but when found, often thicker and more reinforced.
• A Brazen Fake – Perfect, unblemished, purple glass. These fakers were tinted purple so they would blend in, but no glass can get walked on for 100+ years and not get a few cracks and scratches.

If the lenses have turned deep purple, you’re likely looking at a set from the late 1800s to early 1900s.

Can You Restore Vault Lights?

You may think this is a super obscure piece of history, but they are actually important enough that the National Park Service has a preservation technical write up on the process. Despite their decline, there’s good news for historic restoration buffs: you can still get vault lights today! A handful of specialty companies manufacture historically accurate replacements.

Companies Keeping Vault Lights Alive

• Circle Redmont (USA) – Specializes in structural glass products, including modern vault lights.
• IBP Glass Block (USA) – Produces glass blocks suitable for vault light restoration.
• Landmark Glass (UK) – Focuses on historic glass restoration, including pavement lights.

If you’re restoring an old building or just a sidewalk history nerd (no judgment), these companies can help bring the glow back.

Final Thoughts: The Forgotten but Fantastic Vault Lights

Vault lights are one of those weird, wonderful inventions that were both ahead of their time and a victim of progress. They were the energy-efficient lighting solution before energy efficiency was cool, and even though most of them have disappeared, the ones that remain offer a small, fascinating glimpse into a time when sidewalks weren’t just something to walk on—they were also something to look through.

So next time you spot a purple-hued sidewalk panel, take a second to appreciate the history beneath your feet. And maybe, just maybe, don’t step too hard