Could an illusionary light spell like this work?

Question

Would it be possible to create a "light" spell which is under the illusion school of magic instead of evocation like the original light spell is?

My thought was to make a spell which would fail to work on anyone unless they were actively working to accept the spell. Basically the spell automatically fails against anyone who isn't willing.

The purpose of the spell would be to grant the ability to see in light without giving that light to others. So a sneaky light.

Because lets face it, the leading cause of night ambushes are from camp fires, lol.

Answer 1

What you're talking about is spell creation, which is nicely covered in the Ultimate Magic. I don't remember the exact wording offhand, but essentially when your doing something like this, take into account other spells that do something similar to what you're going for, and use them as a benchmark.

In this case, your spell is identical to the spell Light, with the exception that it has a slight tactical advantage for people friendly to the caster. I'd personally bump it up a single spell level for this reason, just because the players I run for would use this spell to set up all kinds of ambushes, attacking in what would seem like total darkness to anyone but themselves.

In short, go for it! Take into account how you think people will use such a spell, and adjust as needed! It sounds like fun!

Answer 2

An Illusion spell could create light, but it would work differently than intended.

As covered elsewhere, there are rules on spell research/design.

However, the illusion effect wouldn't work exactly as you want: a creature would have to interact with the light in order to make (or willfully fail) their Save. Creatures outside of the radius would see the light until they reach it (or whenever the GM deems they've 'interacted' with it).

How it plays out would have to be handled case-by-case by the GM- they'll likely gauge creatures' intelligence and knowledge of your party, and decide usually roll the Save; but even then, a creature could fail the save naturally and not be adversely affected.

Answer 3

To address specifically the idea that "Other creatures easily succeed on the save, but the allies know the effect is beneficial so choose to fail the save":

First, other creatures would not necessarily GET a save to begin with, assuming this would be a figment, since that requires interaction beyond just looking at the illusion.

Second, a creature that disbelieves an illusion can still see it. I am not certain as to how they would perceive indirect consequences of an illusion (i.e. illumination), but I would interpret this as meaning "even if everything else worked, it still wouldn't be very stealthy".

Voluntarily failing the save is less clear, so let's just say that part works for the benefit of doubt.

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The next question is whether such a spell would be an illusion in the first place. I am not entirely familiar with Pathfinder, but unless there is an existing illusion spell which clearly states that it can be used for illumination, I would conclude from "a spell which creates illumination exists in the evocation school" and "no spell which creates illumination exists in the illusion school" that a spell which creates illumination is more appropriate as an evocation even with the other desired features. This might or might not be relevant though.

Based on the way Illusions interact with concealment, I would probably say that having a normal Light spell, then covering that Light with an Illusion that blocks it, would allow for those that disbelieve the illusion to see the illumination as well; it's not entirely logical to me, but there's a reason it's magic. Perhaps a combination of those two effects into a single spell would be valid; if the Illusion spell required for that effect is higher level than the Evocation spell (Light) required for that effect, then I could be convinced that the resulting combined spell would be "more Illusion" and fit the Illusion school despite also requiring Evocation. This would be my solution if having the spell be an Illusion is critical. Otherwise I would probably call it Evocation and base details like spell level and duration on the Communal Darkvision spell mentioned by Hey I Can Chan.

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In conclusion, spells which allow certain characters to see while other characters receive no benefit already exist, and depending on why those aren't sufficient there could be other solutions. But without knowing why the existing option(s) aren't desired the particular inadequacy can't be intentionally addressed. As for the specific mechanics proposed in the question, I would say no an illusion spell which provides illumination to people who fail the save, even if they know it was an illusion in the first place, and does not provide illumination to others because they succeed an intentionally easy save, does not make sense within existing mechanics.

TL;DR: The spell as described does not sound legit, but the desired effect is probably possible some other way.