Figments aren't weird, they're normal. Though they are, he supposes, both magic and "eye things." 

If you insist on describing them as would a toddler.

How's this for a summary:

Figments look like they look like things, but that's a trick and they actually look like other things. But if they look like anything at all, and it's not mind-affecting, they've got to be absorbing light and reflecting it. 

The question is, can they make light too? 

Basically it's a question of whether an illusion can change transparency, translucency, opacity, and reflectivity, and whether illusions can shutter illumination or provide it.

Can you see a figmentary wall of fire in a dark room? If you can, can you see an figmentary wall of ice just as clearly?

If you can't see the wall of ice, can you read by the light of the wall of fire?

Can you create an figmentary spectroscope? 

Since he's already maintaining the silent image, Irevotnin will create a figmentary spectroscope by means of demonstration. 

It produces light - if dimmer light than your eyes might have you believe. 

It doesn't say in the book that silent image can increase the Light Level of a room.

It doesn't say in the book that a wall of fire can, either.

...Fair.

Can you use silent image to make bright enough light to Blind or Dazzle? I'm going to use that trick if I can.

The maximum luminous output of a silent image is far beneath that of the sun, but it seems that way at a glance and can be a useful distraction.

At a glance? Is that a "if they study it carefully they get a save" at a glance or a "this counts as interacting and they get a save" at a glance?

Probably the latter.

Then the permanent image plan is a bust anyway!

Even if they disbelieve the full effect, it still makes some light.

What if we tried more power?

Strung up a bunch of them?

That wouldn't raise the Light Level beyond what one could do.

I think it should.

If putting two candles together weren't brighter than having only one, the campaign setting wouldn't have chandeliers.

Where there aren't explicit rules for something, we use physics or our common sense.

..........

OK.

Hold up a moment...

Wikipedia says that sunrise or sunset on a clear day is 400 lux (lumens per square meter), that an overcast day is 1000 lux, that full daylight is 10,000 through 25,000 lux, that direct sunlight is 32,000 to 100,000 lux.

If we assume that every square meter of the permanent image gives off light like a search and rescue spotlight, 50,000 lumens, and then spread that over 80 miles by 80 miles, aka 6,400 square miles, aka more than 16 billion square meters... that's 0.004 lumens per square meter.

I don't think we can cast the spell enough times for it to matter.

Well, that's one hope dashed. Could we do the same thing but with a brighter spell?

If we can source the diamond, it would be worth it to ask by commune if it can be done with miracle.

And ask whether the shadows would just brave the light if they got hungry.

But we'd need. Well. A diamond.

Hey, I just had a thought. 

If the shadows eat everyone in Cheliax, who's going to guard the Worldwound?

Cressida Kroft hadn't thought of that, and she really, really should have.

And if they eat everyone in Lastwall, who's going to guard against the return of Tar-Baphon?

Geb will be less harmed than its neighbors. They might look about themselves and think the Inner Sea ripe for conquest.

Do you know who else will be relatively unharmed? The gearmen and Iron Gods of Numeria. 

Robots versus demons versus zombies vie for dominance in a world that fell to shadows!

I'll loot a lasergun and make popcorn.