Why is it so hard to replicate natural light using human-made lighting?


There’s something about natural light that seems to permeate a room better than almost lightbulb placed in almost any position. To me, even sunlight diffused through clouds feels more ‘continuous’ and ‘real’ compared to even these ‘natural-light’ light bulbs.

Even if I tried to mimic the sun by placing a bright lamp in the window, it still wouldn’t feel the same – either too bright or not bright enough

Is it because the sun is so far and light bulbs are so close?
Is it the wavelengths of the radiation (and if so, are we still not able to replicate it)?

In: 109

It’s the diffusion-through-clouds (and through the sky in general) that makes the difference. Sunlight gets scattered by the atmosphere and even bounces off the ground outside, so it winds up coming from every direction at once – MORE sunlight is coming from the direction in which you see the sun, but the amount coming from a random bit of blue sky is still enough to light up a room.

To mimic this effect you’d need a light-source the same size as each of your windows. It can be done, but it’s quite expensive so people generally don’t bother.

We do not totally understand the entirety of light. There are certainly bands that we do not see and have not yet learned to identify or quantify. So much left to explore.

There are 3 primary features at play:
– Color Spectrum: The spectral curve of sunlight can be very difficult to reproduce. Spending more on high-CRI LEDs can help a lot with this (especially in the range of 95+ CRI)
– Light spread and scatter: Since sunlight comes from so far away, on a clear day there is almost no spread when coming through a window, the light coming in will all be almost perfectly parallel. On a cloudy day the light is scattered so much that it will be coming in perfectly evenly from nearly every direction. Both are difficult but not impossible to reproduce.
– Light intensity: Light decreases in intensity following the inverse-square law. This means that the closer you are to a light source, the faster the apparent intensity decreases. The sun is incredibly far away, so the light from the sun appears to have the exact same intensity no matter how far away from the window you look. Since a light bulb is quite close, the intensity dramatically decreases as you move further away from the bulb. You can partly overcome this if you use a parabolic lens or mirror to create columnar light (to mimic a sunny day), but not if you’re trying to mimic diffuse sunlight.

Regarding the “wavelengths and radiation” we have actually replicated that pretty well… they’re called tanning beds, and from there you can probably understand why we don’t use those lights for indoor lighting.

(A little oversimplified explanation since tanning beds generally use a slightly different kind of UV light than the sun because it supposedly reduces the chances of sunburn, but the point is, the technology is there)