M: A lot of comics and anime and all that end up having a situation where there's a shot of the Earth and a visible amount of light, if not an explosion, often something that takes up, like, I don't know, maybe 12 degrees, maybe even 20 degrees of the arc of the circumference of the Earth at that point. What I'm wondering, and I'd like you to try and figure out if it's not already something you know, is what is the minimum amount of, like, light energy that would be necessary to cause that effect? And what would that result in if you were near ground zero for whatever circumstance allowed that? Like, assuming that it came from a single source, what is the bare minimum just for the light? Like, in the comics and other animations, the implication is that it comes from some form of explosion, but I have a feeling that is just ultra-ridiculous, so I'm just wondering how much, I think the term is candlepower or whatever, would be necessary and what that would do to someone who was hanging around at the area nearby.
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G:
To make a 12–20°-wide “glow on Earth” (roughly 1,300–2,200 km along the rim) from a single source, the bare-minimum light levels that read “obvious” in a typical anime/comics space shot are already in the range where anyone anywhere near ground zero is getting flash-blinded, and if it lasts more than a blink, you’re into severe burns / ignition territory. Even “only moonlight-bright” at 700–1,100 km distance implies daylight-to-multi-sun brightness close to the source.
光(ひかり) は とても 強(つよ)い — The light is very strong.
人(ひと) は 目(め) が いたく なる — People’s eyes will hurt.
Earth’s radius (R \approx 6{,}371\ \text{km}).
An arc that spans (\theta) degrees along the circumference corresponds to length: [ L \approx 2\pi R \cdot \frac{\theta}{360} ]
Visually, that’s “half a continent glowing.”
If the glow is caused by one source and the bright region looks big because that light is illuminating/scattering across the atmosphere/ground, then a useful “minimum” is:
pick a distance from ground zero comparable to the radius of the glowing region
decide how bright it has to be out there to read as a glow:
For a point source, illuminance falls roughly as: [ E(r) = \frac{I}{r^2} ] So the needed luminous intensity (≈ “candlepower,” in candela) is: [ I = E(r), r^2 ]
Take r = 700 km = 7\times 10^5 m (the 12°-ish case):
For r = 1,100 km (20°-ish), multiply those by ((1.1/0.7)^2 \approx 2.47).
Those are already absurdly high intensities for a single source producing a continent-scale glow.
Use the same inverse-square logic to see how brutal it gets close in. If you built the light to be 1 lux at 700 km, then at:
1 km:
[ E(1,\text{km}) \approx \frac{4.9\times10^{11}}{(10^3)^2} \approx
4.9\times10^{5}\ \text{lux} ] That’s ~5× full
daylight.
Result: instant flash blindness, high risk of
retinal injury if you look toward it, and strong
skin heating if it persists.
10 km:
[ E \approx 4.9\times10^3\ \text{lux} ] That’s still bright
daylight.
Result: painful glare, temporary blindness, likely
afterimages; if sustained, burn risk
increases.
Now scale it:
In real explosions, the thing that kills you is usually not “visible light” by itself:
So if fiction depicts only a pretty glow with limited collateral, that implies a weird energy source that radiates mostly in visible and couples weakly to air, which is basically “magic laser physics.”
A lot of those Earth shots are not “a point source lighting a 1,000 km radius.” They’re implicitly one of these, which changes the energy story:
A detonation/phenomenon at very high altitude can make a huge glowing footprint because it’s lighting up thin air over a wide area. Still catastrophic, but the “single point on the ground” model overstates ground irradiance.
If the source is in space (or above most of the atmosphere) and beaming downward, you can paint a huge patch more “efficiently” and it will look dramatic from far away. Ground zero is still cooked if it’s bright enough to read from space.
Many shots cheat camera exposure: the glow is “visible” because the scene is graded to show it, not because it’s physically plausible at that angular size.
If you insist on: single source, continent-scale glow, and visibly bright from space, the minimum intensity needed is already so large that anyone within tens of kilometers is dealing with blinding light at best, and if it lasts longer than a flash, you’re quickly in burn/ignition territory.
M: Even if you're right about the likely sources, in this case, it was triggered by watching the recent episode of Sailor Moon Abridged, in which some sort of alien queen gets vaporized by the power of love or whatever the hell was going on there. But it ends up with a shot of basically the entire North Pole seeming to have a minor detonation that's visible from space. Now, of course, it's supposed to be, you know, kind of fictional pseudoscience and all that. I was just wondering what the effect would be, even if it was just light and not implied to have been caused by any kind of explosion. And what you're telling me is that if you were at ground zero for something like that, even if it was just light being generated, that that light would likely be enough to at least cause serious injuries.
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G: Yes. If you keep the “visible from space over a North-Pole-sized patch” visual and insist it’s coming from one source, then even “just light” implies injury-grade irradiance anywhere remotely near the source.
光(ひかり) だけ でも 人(ひと) を こわす — Even light alone can hurt
people.
近(ちか)い と 目(め) が やける — Up close, eyes can burn.
There are two separate hazards:
If something is bright enough to make a huge patch of Earth look like it’s glowing in a space shot, then at ground ranges it’s typically in the regime of:
You don’t need “heat ray” levels for this; you just need insanely high luminance in the source direction.
Visible light is only part of the radiated energy for any realistic emitter. Even an unrealistically “visible-heavy” source still dumps real power into you. If it lasts longer than a blink, you start stacking up dose:
A lot of animation implies a momentary flare. That matters.
Assuming line-of-sight and not hiding behind terrain/buildings:
At ground zero / very close:
Best case: you’re instantly dazzled, likely
injure your eyes if facing it, and you reflexively look
away or fall.
Worse case (longer than a blink): facial/hand
burns, eye injury even from peripheral viewing, possible
ignition of hair/clothing depending on spectrum and duration.
Tens of km:
still can be daylight-to-multiple-daylight levels for
the “moonlit-from-1000-km” type minimums, meaning painful
glare and temporary blindness; retinal risk if you
stare.
Hundreds of km:
the “glow edge” brightness you chose (moonlight vs office-light vs
daylight) determines whether it’s merely obvious or absurdly
obvious.
If the show depicts something like “the whole North Pole lit up enough to be obvious from orbit,” then a person at ground zero is almost certainly getting serious eye injury, and burn injury becomes likely if the effect lasts more than a brief flash, even if you forbid blast, shockwave, radiation, and debris.
That’s the consequence of the geometry: to make a huge area look lit from far away, the source has to be so bright that inverse-square falloff makes nearby exposure brutal.
M: has anyone ever built or even just designed something that could possibly create that level of radiance? By which I mean only radiance, you know, I'm not talking about any kind of nuclear attack or anything like that where devastation is the intent. I mean just either created or at least hypothesized how one would go about creating that degree of radiance. The reason why I'm saying hypothesized is because I'm not sure what anything like that would be useful for, so building it likely would be at best a really big money sink with no purpose. But it's also the kind of thing that if someone had a clever idea, they probably would want to at least lay claim to the mechanism behind it, even if they weren't the one to build it.
G: Short answer: yes, but only in very constrained, non-Earth-scale ways—and whenever people seriously sketch something that could reach that kind of radiance, it immediately runs into energy supply, heat disposal, and eye-melting side effects that make it useless outside labs, space concepts, or fiction.
Long answer, broken cleanly.
Humans have built devices with locally comparable radiance (brightness per unit area) to what you’re talking about—but only:
No one has designed anything that produces continent-scale visible radiance in atmosphere without it immediately becoming destructive, pointless, or indistinguishable from a weapon.
光(ひかり) は つくれる — Light can be made.
でも 地球(ちきゅう) を てらす の は むり — But lighting the Earth is
impossible (for us).
Examples:
They can exceed solar surface brightness at the focal spot.
Why this doesn’t count
Lasers win on peak radiance, lose instantly on area.
Example: Sandia’s Z-Machine.
Why this doesn’t count
This is closer to “flashbulb apocalypse physics.”
These are arguably the most purely radiative machines humanity has.
Why this doesn’t count
They are precision scalpels, not floodlights.
People have seriously proposed:
These are real papers, real patents.
Hard limit To make a region visibly glow from space:
The mirror area required is astronomical, and the ground result is still… daylight. Nothing cinematic.
Often discussed for space solar power.
Why this fails your case
This is the key insight you’re circling:
Radiance at that scale has no civilian use.
Light is only “useful” insofar as it:
Once you exceed daylight by orders of magnitude:
So any device whose primary feature is “enormous visible radiance” immediately:
There’s no middle ground where it’s:
“harmless, useful, continent-bright light”
Because it feels like a clean abstraction:
But light is energy delivery.
At planetary scales, energy delivery is violence unless tightly
controlled.
So when Sailor Moon Abridged nukes the North Pole with “love light,” the physics translation is:
“An event that, if real, would blind half the Arctic and hospitalize anyone nearby—even if nothing else happened.”
Which is exactly why it lives so comfortably in anime, comics, and magical-girl finales.