A cloak which, if worn by a light-emitting monster, blocks them from emitting light. Also applies to the player if they are carrying a light source or polymorphed into a light-emitting monster.
Energy vortices should emit radius 0 light, so that when they are in a dark area and you have clear line of sight to them, you can see them (made of whirling energy, they are obviously visible but don’t really throw light on anything else).
New type of terrain, “fire terrain”, a square that is on fire. It displays as an orange period. (If this will be too nasty to people who play with color off, the glyph should perhaps be changed.)
Wands of light should light up when wielded (in a radius of perhaps 3 or 2). To give them some limiting factor, they either lose a charge each time they are wielded, or there is a fixed chance per turn it’s lit that it loses a charge. It’s been noted that this would provide an incentive to try wielding every wand in order to determine if it’s light, but this may not be a big problem.
Firefly, an a monster that is a light source, but a variable one. It ranges from being totally unlit to emitting light in a radius of 3 for a brief time. Is poisonous to eat, and with very low nutrition; has a mild bite attack. Tends to spawn in dark areas.
Internally, the deciding factor when a firefly should light up should probably use its mspec_used variable, which enables them to light up again when it hits 0. Also, cancelling a firefly should prevent it from lighting.
Merge Sunsword and Trollsbane like NetHack Fourk does (a single artifact that emits light, instakills gremlins and instapetrifies trolls, with bonuses to undead), except keep it a morning star and name it Sunflash (because a lot of these consolidated effects have nothing to do with trolls). Having it stay a morning star makes it an attractive choice for Priests, and raises the appeal of training morning star.
Glowstick: a tool that can be applied to make it emit light in a radius of 2. It lasts a few thousand turns before dying (reducing to radius 1 light when near the end of its life), but cannot be turned off like a candle or lamp can.
Gold dragon armor’s light radius is increased by 1 if its enchantment is above some amount such as +5.
Glowworms, a w monster that emits light in a radius of 1. Maybe they have a blinding bite attack, but that may be taking the light theme a bit too far.
One of the prayer boons you can get from a god is intrinsic light: you become a light source (probably of radius 3, but could be 4). Crowning may give you this permanently, since you’re now all holy.
Sconces (perhaps a \ found on the walls of dark rooms, and in dark Mines levels, that may contain (lit or unlit) candles. You can untrap or loot them to remove the candle. Could also generate with an oil lamp, which would give you a potion of oil or a partially filled oil lamp when looted.
Artifact brass lantern that gives light in a radius of 4. Invoking it recharges it.
The scroll of light gives the player a light radius of 3 for a temporary amount of time, rather than lighting up a fixed area.
Undead caught in a flash of light (from cameras or just from casting an area light spell) get awakened if they were asleep or confused (with a chance that decreases at higher levels) if already awake. Possibly, just illuminating their space by carrying some light source near them should be enough to wake them up.
Being engulfed by a solid monster makes you blind unless you are carrying a light source, because it’s dark in their stomach.
Magical sources of light that light up a fixed area are temporary, and revert to darkness given time.
Shining spellbooks give off as much light as a candle when wielded.
Fire trap effects, fire explosions, and camera flashes light up a large area, but only momentarily, before it goes back to darkness.
Wielding a light source increases its radius by 1. Or possibly 1 if offhanded and 2 if directly wielded.
Elves get low-light vision, which doubles the radius of light sources, rather than infravision. It also gives them vision on dark squares that are orthogonally or diagonally adjacent to a lit square.
Fire elementals and vortices have a light radius of 2, not 1.
Archons emit light, in a radius of 2 or 3.
New artifact The Phial of Galadriel. It is a potion of water (potion of starlight in dNetHack) that acts as an infinite light source which scares giant spiders and Nazgul that come into it, and can be invoked to bless 1 item. May need more powers to make it better, and behavior for what happens when you drink it, but these are unspecified.
Make candle stacking for more light actually useful and realistic: the number of candles required for another square of radius increases quadratically instead of exponentially, so 1 candle gives radius 2, 4 give radius 3, 9 give radius 4, 16 give radius 5, etc.
Later extended into a more general idea allowing light sources of any type to stack: candles each give 5 lumens (because a single candle’s light reaches up to sqrt(5) squares from the center), lamps give 10 lumens, potions of oil 2, and the full Candelabrum gives 20. To compute your total light radius, add up all the lumens and take the square root. (Note that this exact formula might scale too fast: 4 candles equals the Candelabrum).
Candle additions:
Uranium wands glow in the dark (radius 1).
