I was literally walking around Lighthaven a few hours ago with someone who was trying to figure out why the spaces all felt so good. So this is extremely timely.
Lighthaven is a really impressive aesthetic achievement and I'm really happy not only that it exists to host worthwhile events, but as an additional bonus you're willing to share your secrets of forgotten photonic lore. That's pretty cool.
1I’m somewhat skeptical of the importance of ultra high CRI. I don’t doubt that 80 vs 95 makes a difference, but I’m not sold on 95 vs 98, since it seems susceptible to placebo and is confounded in the wild by other lighting design factors. What convinced you?
"I ask the fundamental question of rationality: Why do you believe what you believe? What do you think you know and how do you think you know it?
Along those lines, I understand what it is you believe, but I don't feel like I have a very good understanding of why you believe it. I guess a combination of "the closer our environment matches the ancestral environment, the happier we tend to be", "personal experience introspecting on what I like", and "experience talking to people about what they like"?
Relatedly I am not clear on how confident you are in your claims but am interested in knowing how confident you are in your claims.
Personally, I spent some time recently digging into lighting. Amongst other things, I did a little (informal) experiment using an app to measure lux (and color temperature) in various places to see how they made me feel. Hopefully I'll write more about this some time, but in short, I feel like up to 1,000 to maybe 1,500 lux it felt better, but I don't feel very confident about that. It's hard to say, and there are lots of potentially confounding variables.
As for CRI, my research wasn't very fruitful. The impression I got was that 95+ CRI is useful in contexts involving things like photography and art but not in everyday scenarios, and that brightness is way more important for things like focus and mood. I hadn't realized that outdoor lighting has great CRI though; I find the evolutionary reasoning to be plausible, so the fact that outdoor lighting has great CRI makes me more bullish about CRI having a more meaningful impact on things like mood and focus.
Maybe I'll write more about this too, but FWIW, I felt like I was spending too much time researching all this stuff and figuring out what products to buy, so I kinda just punted and bought the Brighter Lamp. It should last like 20+ years and at that longevity, it's like $5/month. Whatever.
A different interpretation as to why high CRI may be preferred by our visual system is from the predictive coding perspective and how color constancy works in visual perception.
If we take color constancy processes to be our mind trying to predict what the surface reflectance of an object is given the available information, then the wider the spectra of the illumination source, the better the cues our visual system has access to for inferring the surface colors of objects. You could imagine an extreme where you have a single wavelength light source like a sodium vapor lamp (the orange lights that might illuminate a parking lot) and how that impacts your ability to differentiate colors of objects in your environment, since different surfaces would give your eyes the same information in that lighting environment. You would be unable to differentiate between several surface colors, and this is a widely done demonstration in psychology perception courses. This would be the worst case scenario and corresponds to a low CRI, whereas a high CRI light would give you better information about the colors present in the environment.
Better information leads to less guesswork by your visual system and minimizing prediction error might be something preferred by your mind.
Relatedly, having bright enough lights to activate your cones for color perception also matters. In dim environments we mostly use scotopic vision through our rods, which does not allow us to perceive color since it is a single receptor system. Anecdotally, I prefer times of the day where sunlight contains the more broad spectrum versus near sunset when it is both distorted by our atmosphere and also dimmer to the point where you start to perceive less color. The latter point can also be observed more saliently during solar eclipses. The spectra remains the same since the sun is not distorted by our atmosphere, but nevertheless dims enough that you start seeing less color around you outside.
My flat came with "energy saving" bulbs which were fluorescent (even worse than LEDs) and capped at 13W. I couldn't even plug in 18W fluorescent ones into the socket, because the plastic shape is different (even though the electrical connections are the same). I put "energy saving" in scare quotes because they're in large party energy saving by just being dark. This led me to suffer quite bad SAD for the first and only time in my life. It took until the second winter to figure out that this was what was going on and put in some high-power LED bulbs. Now I'll have to check for CRI!
I put "energy saving" in scare quotes because they're in large party energy saving by just being dark.
Huh, no, a 13 W incandescent light bulb would be very dim
Why does this post say '29 min read, 7,100 words' - could it be something to do with the embedded interactive elements, maybe the code for those is automatically counted by the reading time estimator? Minor, but seems worth fixing if the bug occurs elsewhere too.
1I’m sceptical of this being a universal rule because I don’t know why you believe what you believe. However, I want to scream “preach!” because empirically I agree 100%.
I don’t know if it is my theatre background, but another thing I find severely underappreciated are textured shadows. Worse than a blue LED is only a bright blue LED in the middle of the ceiling as the only light source.
I think (based on photos), it is another thing Lighthaven does really well!
1Hmm: in the simulated example, I indeed prefer the the CRI 100 matched reference in every example, except for what it does to the wall color. But the stronger preference for me is clearly that I prefer the cooler (as in, higher temperature) sources. I think this is why the wall color often gets worse for me.
At home I have a room whose lighting makes me feel like I'm dying a little (seriously, it makes me sad and tired, I hate it!). It feels like it's because of the yellow/orange, and also I think it's an incandescent light? Compare to how I actually light the room, namely a lamp whose higher temperature blues and whites are actually pleasant. I think that one is an LED? I'll try to remember to check and update this whenever in months next time I'm there.
Lastly, look at this guy who made an artificial sun. Key features are making the light have parallel rays via a lens (so that e.g. shadows don't change size) and using soapy water to make diffuse blue. Isn't this just so cool?
1The world got ugly when we invented LEDs
I don't know if it's just me, but whenever I see lone, undiffused LEDs (such as on string lights or light strips), it is immediately obvious that they're LEDs because of the "aliasing" or "shimmering" effect I see when my eyes saccade back and forth. This is a stroboscopic effect and so even the best CRI doesn't prevent this. For this reason (and on the recommendation of this article) I've made sure to only get incandescent string lights for my own use.
(Sometimes when I see a Christmas tree strung up with LED lights, I can even tell that half of the bulbs are on a circuit whose cycle is 180 degrees out of phase with the other, because the lights shimmer in opposite directions.)
LEDs strobe when they're run at less than 100% duty cycle or on a half-wave rectifier. They should shine steadily when run at 100% on DC power.
Though I find the LED shimmer to be rather less unpleasant than fluorescent lamps (classic tubes or CF bulbs), which flicker in time with the AC power and have rather incomplete spectra that make pale-skinned people look greenish and often make an audible hum.
https://science.nasa.gov/asset/webb/spectrum-of-a-fluorescent-light-bulb-vs-spectrum-of-the-sun/
This is caused by low quality power supplies, which are extremely common in string lights. It's not affected by CRI.
Fun fact: string lights are considered "decorative", and so it's nearly impossible to buy high quality ones unless you purchase components and assemble them yourself.
I've designed a few spaces people seem to really love, most widely known Lighthaven.[1]
Most people have surprisingly bad introspective access into why a space makes them feel certain things. Often the most we can do is "this place feels fake", or "this place has bad vibes", or "this place feels cozy". It took me many months of practice to get to the point where I could tell why a room made me feel off, or why it made me feel warm and cozy, or alert and energized. Luckily you don't need to do that because the answer most of the time turned out to be the same.
Usually a space feels bad because it is lit by low-quality lights
Our eyes evolved to see things illuminated by sunlight. Correspondingly the best proxy we have for whether the light in a room "works" is how similar the light in that room is to natural sunlight. The most popular way of measuring how much light differs from natural sunlight is the "Color Rendering Index" (CRI):
The everyday situation where I've found the effect of low-quality lighting starkest is to look at the face of a person illuminated by nothing but a computer screen. Computer screens emit extremely low CRI light, as a screen simulates white by combining the light from red, green and blue LEDs, producing a very low-CRI emission spectrum. Faces illuminated by nothing but screens often look off and have a slightly alien, plasticky, often blue-feeling quality to them, even if the screen that is emitting the light is almost fully white.
In short: If you want a space to feel natural, buy lightbulbs with at least 95 CRI, ideally 98.
But I thought my eyes can only see three colors?
Yes, and that is exactly why when you look at a computer screen directly, colors look real and vivid. Your computer screen emits light that (pretty precisely) stimulates the three kinds of cones in your eyes and so can produce basically arbitrary perceptual colors (it's not perfect, but it's quite good).
The problem occurs when light bounces off of other objects in the room. The color of an object is determined by how it absorbs, reflects, and changes light that hits it. For example, an object under sunlight might completely absorb orange light (~630nm), but fully reflect the red light and green light emitted by the LEDs in your computer screen. That object would look unnaturally bright under the light from your computer screen, because it basically reflects all the light from your screen, but under sunlight it would absorb all orange wavelengths.
So to a first approximation a light feels "natural" if its light emission spectrum is a smooth curve. Sunlight, as well as any other light created by burning or heating things to really hot temperatures, has a smooth emission spectrum, which maintains all color information as it bounces around a room.
You might have noticed a second number that keeps showing up in the widgets above, often formatted as "5000K" or "2500K". This is the "color temperature" of light. We call this "temperature" because it corresponds to what kind of color objects emit when you heat them to that temperature[2]. Objects that are hotter, emit light that is more blue. Objects that are less hot (e.g. "only" 2000 degrees Kelvin) emit light that is more red. Naturally we call red light "warm light" and blue light "cold light"[3].
If you are lighting a room with plenty of natural light, just use 2000K-3000K lights
People prefer bluer light during the day, but redder light during the evening and morning. Sunlight is really really bright, so what lamps you have in your room do not matter if you have large windows during the day. This means the primary purpose of your lights are to light things in the evening and morning. This means they should be warm.
If your room does not have much natural light, I recommend having bright overhead lights that are closer to 4000K, and dimmer floor lamps around 2000K-3000K.
The world got ugly when we invented LEDs
For basically all of human civilization up until very recently lighting quality was a complete non-issue. Why? Because all of our artificial light sources consisted of heating things to very hot temperatures, or burning things. When you do that, you basically always emit natural light with a smooth emission spectrum.
Lighting quality only became an issue within the last 100 years with the introduction of fluorescent lamps in offices. This is why "fluorescent lighting" has for many people become the best shorthand for fake or artificial lighting.
But people's homes, as well as any entertainment venues, bars or really anywhere where people socially congregated in the evenings were lit by incandescent light bulbs (or before then, candles and oil lamps) with perfectly smooth spectra.
But around 30 years ago home lighting LEDs were introduced, initially with truly terrible color rendering indexes, and most people unable to put words to the discomfort and alienness they caused, chose the energy-saving option and replaced their incandescent bulbs with LEDs. Eventually, in most of the western world outside of the US, incandescent lightbulbs were literally banned to promote energy saving policies.
This was the greatest uglification in history. Within two decades, much of the world that was previously filled with beautiful natural-feeling light started feeling alien, slightly off, and uncomfortable, and societal stigma around energy-saving policies prevented people from really doing anything about it.
But you, within your home, can fix this. LED technology has come along way and we can produce high-CRI LED bulbs (I recommend YujiLED or Waveform Lighting). The world really used to be much more beautiful and a much less harsh place in this one respect. You can restore the natural light, and the homeliness that all your ancestors felt, at least within the confines of your home. Just buy some high-CRI, warm color temperature light bulbs. There is a lot more to interior design, but it's honestly so much easier to iterate on than lighting.
But before that the Lightcone Offices, and I've also played a role in designing some of the most popular areas at Constellation. Also of course credit to my team for much of the work.
What kind of object? Well, turns out really any object, unless the thing you are heating undergoes some specific chemical reaction when you heat them that causes them to emit other wavelengths of light. The radiation curve that most objects tend to follow here is known as the "blackbody radiation curve". You can google it or ask your local LLM if you want to understand the physics behind this better.
This is a joke. This is indeed exactly backwards. You cannot imagine how much this makes explaining color temperatures to people more confusing. "Oh, just get the warmer light bulb, no not the one that has the higher temperature written on it why would you think that, that would produce much colder light". Grrrr.