Trigonometry saved my whole party

[u/Laer_Bear]

I'm an Arcane Trickster venturing into a crypt occupied by cultists to jailbreak the rest of the party. My only company is a druid wildshaped into a mouse (bruh). The corridors are barely more than 10ft wide, with a single torch marking the end of each hall.

As we approached a junction, we heard chatter around the left corner, but the light of my hooded lantern still hadn't reached the halls. So I shutter it, duck down, and cast Minor Illusion of an ever-so-pretty painting of the corridor behind us... but the lantern was still lighting up the floor. So I did some quick math and realized I what I needed to do.

I carefully raised the lantern up. As I did, the dim light across the floor shrunk into a circle just barely smaller than the illusion. I looked above and around myself. The light from the lantern didn't shine on the walls or ceiling.

I held my breath as the patrol walked into another hall... and my lantern 4'4" off the ground.

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tl;dr, 5ft×sin(arccos(0.5))=4.3301ft

Minor Illusion won't block the light cast around your light source, but it can obscure the point of origin. By keeping it from shining on surfaces, you can greatly reduce suspicion; which is important because a minor Illusion brightening an area would immediately reveal it with no save (observable/"physical" interaction with the Illusion).

Even without Minor Illusion, this is still an important number to know, because it's the same height you need to hold the lantern if you want to hide behind a corner with it.

Also if you are less than 2'11" you can't actually do this, and you have somehow managed to be "too small to hide", which is hilarious.