Glow

Version 0.30: This article may not be up to date for the latest stable release of Crawl.

Not to be confused with magic contamination, which was once simply called glow.

Glow (backlit) is a status effect that does the following:

Makes you easier to hit. Attackers gain 1 + 1d8 to hit against backlit targets.
Prevents you from going invisible.

Sources

Glow can be inflicted by the following sources:

The Corona spell.
Sticky Flame also inflicts the glow status.
A halo inflicts glow on everything inside it. If you are emitting the halo, monsters won't get a to-hit bonus against you.
If your magic contamination is above 5000 (yellow), then you'll glow.
Ru's Aura of Power inflicts the status on monsters.
Evoking a piece from Xom's chessboard has a 10% chance to inflict Corona.
The Meteoran species has an innate glowing mutation.