In a lot of settings that have magic, there's usually some kind of spell that creates a magical light. Often these spells are hand-waved as being completely safe (e.g. it's not actual light and just makes things look brighter), but that's not what this question is about.

Light carries actual physical energy, and as many kids with a magnifying glasses have discovered, you can even light things on fire with it. Even a fairly dim incandescent lightbulb produces a lot of heat and can be a significant fire hazard.

It would stand to reason then that a magic light spell might have similar effects and pose similar hazards.

And spells that conjure balls of light might be particularly hazardous, since then you could potentially end up directly irradiating cell interiors and directly dumping all of the light energy into whatever solid object the spell happens to intersect with.

This might depend though on exactly what sort of light is emitted. I would suppose that a spell that emits 5000K blackbody radiation would probably be worse than a spell with a narrower band or only a single wavelength, but I'm not sure. There's also a bunch of other factors, like if it's coherent, if it's directional or anisotropic, and in the case of a light orb, whether it's being emitted from the entire ball or just from a spherical shell.

How dangerous exactly would different sorts of magic light spells actually be? Also are there any other interesting physical consequences?

  • $\begingroup$ What magic light spells? I didn't realize there was a classification of them somewhere. $\endgroup$
    – sphennings
    Dec 21, 2017 at 19:36
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    $\begingroup$ If your spell is magic, then why does it have to generate waste heat at all? An LED only generates a few watts of waste heat, and is generally cool to the touch. Magic could have even better efficiency. $\endgroup$
    – kingledion
    Dec 21, 2017 at 19:53
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    $\begingroup$ It's magic. If you say it produces light and nothing else, it does. If it is as efficient as a light bulb of your preferred kind, or less, or more, then it is. Side effects may be heat, x-rays, mana or mild curse. Your pick. And do on. $\endgroup$
    – Mołot
    Dec 21, 2017 at 20:00
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    $\begingroup$ @AJMansfield I sit under artificial lighting all day and I haven't gotten burned yet. I guess I don't understand what you think the problem is going to be? I mean, if you make the light some million lumen search-lamp, that might cause trouble, but regular household lightbulb is nothing. $\endgroup$
    – kingledion
    Dec 21, 2017 at 20:06
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    $\begingroup$ While many voted to close this question as opinion based I feel the need to point out that the issue might rather be that you are not posing a problem that can be solved but are asking for an open list. List questions are bad due to the Q&A format of these sites. How is one answer better than another? Is an answer that list 200 things better than one that in-depth explains 1 thing? $\endgroup$
    – dot_Sp0T
    Dec 21, 2017 at 20:58

2 Answers 2


There are a few ways of looking at this, like you said

Safe Magical Light

Per here 900 lumens (a bright, sunny day) is only about 15 Watts of limited-spectrum lighting, and maybe 60 Watts at a wider spectrum that includes infrared. The average human body, at rest is putting off about 100 Watts of power. So, the extra heating may be moderately uncomfortable in the full-spectrum/high-power case, but probably almost unnoticeable in the limited-spectrum/low-power case.

What makes coherent light dangerous is the focusing of power on a small space, increasing the Watts per meter squared. Maybe a magician is only strong enough to keep the W/m^2 at or below a certain threshold, which is why stronger magicians can fire killing beams (or throw around lightning). Power is also related to frequency (E=hc/lambda), so saying a magician is limited to a certain W/m^2 covers emission of cosmic radiation or other very high energy/dangerous light. There are two orders of magnitude between the wavelengths of the bottom and top end of the visible spectrum, so you could very well constrain wizard-produced light to the useful, but not dangerous regime.

If a wizard could fine tune the produced light, it could be beneficial to illuminate plants with just the right frequency and amplitude internally, bypassing dirt, wax, cell walls, and whatever.

Dangerous Magical Light

Going in the other direction, one author had proposed that wizard light was created by the magician evoking a tiny amount of matter converting itself directly to energy at the wizard's command. For the wattage of a typical LED, that would be about 100 femtograms per second (if I'm doing the math right) of mass/energy conversion. This would be unsafe (really unsafe) unless the wizard took extra precautions to filter or frequency shift the light - so, in this case, the magician could pull out the stops and let a light be silently harmful (baleful light), instead of helpful. However, something simple like water or even air should capture the high-energy light past a certain distance.

Another used concept is that magic is pulling from alternate realities or extra dimensional spaces. In those cases, too, unless the wizard is taking additional measures to filter the light, there should be some high-energy dangerous light being emitted with the good.


If the energy to light efficiency is very high, like in a LED or higher, and of similar power (<20W) then all that there may be is discomfort and glare depending on the color of the light.

In particular, if the light contains a dominant fraction of blue light, it may be painful or damage the retina on the long run.

Reference: http://www.ledsmagazine.com/articles/2010/11/light-and-human-health-led-risks-highlighted.html


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