I have now had a few years of experience doing architectural and interior design for many spaces that people seem to really love (most widely known Lighthaven, but before that we also had the Lightcone Offices, though I've also played a hand in designing some of the most popular areas at Constellation a few years back).
Most people (including me a few years back) have surprisingly bad introspective access into why a room makes them feel certain things. Most of the time, people's ability to describe the effect of a space on them is as shallow as "this place feels artificial", or "this place has bad vibes", or "this place feels cozy". And if they try to figure out why that is true, they quickly run into limits of their introspective access.
The most common reason why a space feels bad, is because it is lit by low-quality lights.
Our eyes evolved to see things illuminated by sunlight. Correspondingly, it appears that 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 best illustration I have found for the effect of low-CRI lighting 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. Faces illuminated by nothing but screens often look off and have a "fluorescent" off-color vibe to them, even if the screen is almost fully white.
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 and correct. Your computer screen omits 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 that hits it, but under sunlight it would absorb all the orange light that hits it.
So to a first approximation the primary determinant of whether a light produces "natural" reflections is whether it's light emission spectrum is a smooth curve. Sunlight, as well as any kind of light created by burning or heating things to really hot temperatures produce smooth emission spectra, which maintains all color information as it bounces around a room.
You might have noticed a second number that keeps showing up in the widget 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[1]. 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"[2].
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.
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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.
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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.
Discuss