Backing a Brighter Future
Our investment in the artificial sunlight company, Sunday Light.
Most of us dramatically underestimate how much light shapes the way we feel and function. People like Andrew Huberman and Peter Attia have helped popularize the science behind it, but the core insight is simple: light is a powerful regulator of human biology.
One of the first clues about the link between light and health came in the 1980s with the recognition of Seasonal Affective Disorder (SAD), a type of depression that follows the seasons. As daylight hours shrink in the fall and winter, mood and energy decline. When longer days return in spring, they improve.
Since then, research has gone much deeper. Light influences sleep, mood, alertness, metabolism, and immunity. Poor circadian health has been linked to sleep disorders, weight gain, cardiovascular disease, weakened immunity, and higher cancer risk. The timing, intensity, and spectrum of light are all signals our internal clock uses to regulate the body at a cellular level.
How to optimize light exposure
Trying to optimize light exposure for health can turn into a rabbit hole. However, we can distill the research into two simple points:
- Get as much bright light as you safely can in the morning and throughout the day. “Safely” means don’t stare at the sun and wear sun protection when necessary.
- As evening turns into night, move from dimmed lights to as little light as possible.
If you do just those two, you’ll already be ahead of most people.
To go a bit deeper: timing matters. Morning exposure should happen at roughly the same time each day, and evening dimming should be consistent too. Spectrum matters as well – cooler, blue-rich light works best during the day, warmer light at night. That’s the logic behind blue-light glasses (helpful at night, counterproductive during the morning and day).
Between the two main points above, I’ve personally found the second one easier to follow. I avoid screens at night and utilize blackout curtains in my bedroom. If I do need to be on my computer, I use Night Shift to warm the colors. I also set up smart bulbs around my apartment that automatically shift to redder light as the sun sets. It looks a little strange (I usually switch it off when friends visit), but I sleep well and typically wake up feeling refreshed.
Point #1 is tougher for me because I often spend most of my day indoors. It’s also easy to skip morning outdoor light if I’m busy. For years, my solution was simple: step outside right after waking up and take a short walk. I used to live in a very walkable neighborhood in Boston, and those few minutes made a real difference in how I felt all day. When I moved to my current apartment in NYC, that routine fell apart. I love my new spot, but the immediate surroundings aren’t as walkable. I started missing that morning light and the energy boost it gave me.
Like many VC investors, I believe technology can solve just about anything. So I went looking for an indoor light bright enough to deliver the same benefits as sunlight. To understand what “bright enough” actually means, we need to understand how light is measured.
Lux vs lumens
Light is typically measured in lumens and/or lux. Lumens measure the total amount of visible light that a source emits in all directions. Lux measures light intensity at a specific distance away from the source. It’s expressed in lumens per square meter. So while a bulb might always emit the same number of lumens, the lux you experience depends on distance: the farther you are, the less light reaches you (as seen below).
The gold standard for morning light exposure is 5,000–10,000 lux for 30–60 minutes soon after waking. That’s usually enough to signal to your brain that it’s daytime and kick your circadian rhythm into gear.
The good news is that daytime sunlight is almost always bright enough for this circadian signaling. On a sunny day, it can reach 50,000–100,000 lux, which means you can hit your target in 10–15 minutes. A cloudy day delivers 10,000–25,000 lux, which means you’ll need roughly 20–30 minutes.
Indoor light, however, is a different story. A bright room with lots of windows might give you 1,000–5,000 lux. A typical office delivers only around 300–500 lux. That’s far too dim, even if you’re there all day.
SAD lamps
The problem is that most of us spend our days in those dim spaces, getting maybe 500 lux when we need 5,000 or more. One well-known fix is the SAD lamp, designed to deliver bright, concentrated light.
These lamps offered the first causal proof of what the recognition of SAD had only hinted at — that light itself can directly shape mood and energy. In the 1980s, clinical studies showed that exposure to SAD lamps eased symptoms of seasonal depression, often as effectively as SSRIs. Most lamps advertise 10,000 lux.
But that number doesn’t mean much without context. As we just covered, lux depends on how concentrated the light is, dictated by distance from the source. For most SAD lamps, the advertised 10,000 lux rating only applies if your face is about 12 inches away. In practice, that means sitting a foot from the lamp for 30 minutes to hit your daily goal. This is hardly realistic for most people, especially those already dealing with low energy or mood.
A different approach: Sunday Light
That’s what led me to Sunday Light. Their goal is simple but ambitious: build lights that mimic sunlight as closely as possible. Instead of a small desktop lamp you have to sit inches from, they built a ceiling-mounted light that produces 34,500 lumens – roughly the equivalent of 20 car headlights. The key is intensity at a distance: 10,000 lux at two feet, 5,000 lux at four.
That changes the experience. You don’t need to sit still with your face in front of a lamp. You just live your life in the space below it — working, eating, reading — and still get the light your body needs.
Here is what the light looks like.
It’s a clever design. The LED shines upward onto a reflective panel that mimics the light scattering that occurs in the Earth’s atmosphere. That makes it comfortable to sit under and gives the impression of sunlight in a blue sky rather than a spotlight. The reflective panel also helps the light produce full-spectrum white light, similar to natural sunlight. The spectrum is tunable from warm candlelight (2,650 K) to cool daylight (6,000 K) and can shift automatically throughout the day.
The founder and the company
Sunday Light was founded by Nat Martin, who studied circadian rhythms at Oxford with Professor Russell Foster. Professor Foster, now an advisor to the company, is the neuroscientist who discovered the cells in the eye that regulate circadian rhythms.
After finding Sunday Light online during my own hunt for a better indoor light, I reached out cold to Nat to learn more. He replied seven minutes later, and we set up a call.
Nat embodies one of the core traits we look for in founders: product obsession. He took our first call from his workshop in London, lit by a stunningly bright glow (surprising for London!). On our second call, he was in a hotel room in SF after installing a light for a customer. When I asked about one of the light’s electrical components, he immediately reached off-camera and held up the exact part. He had packed spare components in his suitcase so that he could keep tinkering while traveling. That level of obsession is rare, and it shows in the product.
The first units are expensive because each one is hand-built in London at low volume, but costs are falling quickly. The company plans to offer a range of products as production scales, from more affordable floor lamps to large commercial ceiling installations. Even at current prices, demand is strong. Without any marketing, they’ve had a large number of inbound requests.
Early adopters like Andy Matuschak and Akshay Kothari have written positively about it on X. Sahil Lavingia, a friend of the firm since our 2012 seed investment in Gumroad, had bought one for his office in Brooklyn, so I went to try it for myself. Sitting under it really did feel like sitting in sunlight.
Why we invested
After speaking with Nat and testing the product, the decision to invest was obvious. He combines scientific depth with genuine product obsession, and the device solves a real problem in a way that’s usable and delightful.
We led Sunday Light’s pre-seed round because circadian health is a universal issue, and this is the first product we’ve seen that can scale a real solution. The science is clear that we need more light. The current options don’t deliver. Sunday Light does.
You can learn more or order one here. In the meantime, the timeless advice still holds: get outside when you can.