BXDMG (WIP): Light & Vision

In support of my continuing work towards a BX DMG, here's where my Light & Vision rules stand. (BTW, you'll note a reference to Campfire rules. I'm still working on those, but should have them up here next week some time.) As always, if you think something seems off or could use some tweaking, please let me know in the comments section.

Light & Vision

Vision depends upon the amount of available light. Creatures relying on normal sight require illumination to see clearly. Darkness conceals hazards, obscures monsters, and limits exploration. Managing light is therefore one of the most important aspects of dungeon adventuring.

Every location falls into one of four light levels.

• Bright light allows creatures with normal vision to see clearly. Color, movement, writing, tracks, and fine details are readily visible. Examples of bright light include: daylight, sunlit rooms, a magical light spell, within a few feet of a campfire, close to a lantern.
• Low light provides enough illumination for ordinary travel but not for careful observation. In low light, characters can walk safely, recognize creatures, fight normally, and navigate familiar terrain. However, in low light, small details become difficult to notice. Examples of low light include: twilight, the light of a full moon, the outer edge of torchlight, or a large chamber faintly illuminated by distant fires. The DM may, at their own discretion, require extra time, appropriate ability checks, and/or modifiers in order to notice hidden details.
• Dim light barely illuminates the surroundings. In dim light, characters can usually distinguish walls, doorways, large objects, movement, and silhouettes, but cannot reliably distinguish facial features, colors, writing, hidden doors, fine mechanisms, tracks. Under such conditions, the DM should only describe uncertain shapes rather than precise details (e.g., “Something crouches beside the pillar,” rather than “an orc stands beside the pillar.”) 
• Darkness provide no useful vision whatsoever. In darknesss, creatures relying on normal sight are effectively blind. They cannot read, search, identify creatures, fight accurately, or detect most hazards visually. Other senses function normally.

Typical Light Sources

Light Source	Bright	Low	Dim	Duration
candle	5'	10'	15'	6 turns (1 hour)
torch	15'	30'	45'	6 turns (1 hour)
hooded lantern	20'	40'	60'	24 turns/4 hours (1 flash of oil)
bullseye lantern*	30'	60'	90'	24 turns/4 hours (1 flash of oil)
campfire, small	20'	40'	60'	See “Campfires" (p.00).
campfire, medium	30'	60'	80'	See “Campfires" (p.00).
campfire, large	40'	80'	120'	See “Campfires" (p.00).

*A bullseye lantern illuminates only its forward cone. It typically has a fixed convex lens and a static internal mirror that shines line in an arc of approximately 50°.

Special Lighting Conditions

LIGHT OVERLAPS: When multiple light sources overlap, use the brightest available illumination. Natural lighting does not “stack” to create brighter light. Several torches do not double their radius, but they may eliminate shadows or illuminate a larger area.

BLOCKING LIGHT: Light does not pass through closed doors, solid walls, heavy curtains, thick fog, or dense smoke. Corners cast shadows. A single torch rarely illuminates an entire dungeon chamber.

CONCEALING LIGHT: Light advertises a party's presence. In dark underground passages, a torch or lantern may be visible from hundreds of feet away down a straight corridor. Monsters often notice the light before they hear approaching adventurers.

CARRYING LIGHT: A character carrying a light source usually occupies one hand. The may prevent the use of two-handed weapons, bows, and shields (if the shield hand carries the light). Lanterns may be hung, placed on the ground, or set upon furniture when circumstances allow.

EXTINGUISHING LIGHT: Light sources may be extinguished by circumstances such as a strong wind, deep water, deliberate action, lack of fuel, or magical darkness. Relighting a torch or lantern generally requires one combat round if suitable flame is available.

Extraordinary Vision

While infravision is a standard extraordinary form of vision in the game, some campaigns may feature additional forms of sight. These optional abilities may be assigned to monsters, player ancestries, or magical effects at the DM’s discretion. Unless otherwise noted, these abilities function only to their listed range.

Infravision

Infravision allows a creature to perceive differences in heat rather than visible light. Warm-blooded creatures, recently disturbed objects, open flames, and lingering heat sources appear as varying intensities of brightness against cooler surroundings. Infravision functions best in complete darkness and becomes increasingly unreliable in brightly illuminated areas or near powerful heat sources such as large fires, lava, or furnaces. 

Infravision cannot normally see through solid objects, detect hidden doors solely by sight, read writing, distinguish colors, or recognize paintings or heraldry. It merely reveals heat patterns rather than visible detail.

Heat Interference: Infravision functions by detecting heat rather than visible light. Nearby heat sources—including torches, lanterns, campfires, lava, and similar sources—reduce or negate its effectiveness by masking the subtle temperature differences it normally detects. Creatures carrying a light source generally rely on ordinary vision instead of infravision until the light is extinguished.

Ultravision (Optional)

Ultravision allows a creature to perceive ultraviolet light naturally present in sunlight, moonlight, and starlight. Even on a moonlit night or beneath an overcast sky, creatures possessing ultravision can often see remarkably well outdoors. It is most useful for night travel, recognizing distant movement across open terrain, tracking beneath moonlight, and recognizing distant movement across open terrain. 

Ultravision functions only where the sky is visible or where ultraviolet light is otherwise present. It provides no benefit underground or within enclosed structures where ultraviolet light is absent. 

Ordinary torches, lanterns, candles, and similar light sources neither improve nor hinder ultravision.

Darkvision (Optional)

Darkvision allows a creature to see in complete darkness without relying upon heat. Within its listed range, darkness is perceived as though it were dimly lit. Objects remain visible but lack fine detail and appear only in shades of gray. Darkvision does not reveal color, not does it improve vision in fog, smoke, magical darkness, or other effects that specifically block sight. Because darkvision is unaffected by heat, it functions normally around fires or lava.

Low-Light Vision (Optional)

Creatures with low-light vision make exceptionally efficient use of even the faintest illumination. Whenever at least a small amount of natural or artificial light is present, they see as though the illumination were one step brighter; that is, dim light appears as bright light and low light appears as dim light.

Low-light vision simply makes existing light go farther. The creature's eyes are exceptionally sensitive, allowing it to make use of illumination that would be insufficient for normal sight. Because it is still seeing visible light, everything appears in full color. A creature with low-light vision can distinguish painted heraldry, identify the color of potions, appreciate artwork, and notice bloodstains just as well as a human standing in bright daylight—provided there is at least some light available.

Low light vision does not provide any benefit in complete darkness.

Supernatural Visual Abilities

The vision types presented above describe the natural means by which creatures perceive the world. Some monsters, magical beings, and enchanted individuals possess additional supernatural forms of sight that transcend normal vision. Abilities such as seeing invisible creatures, perceiving through illusions, viewing the true forms of shapechangers, or seeing through solid objects are not separate vision types, but extraordinary powers granted by magic, divine favor, or other supernatural means. Unless an ability specifically states otherwise, extraordinary vision supplements a creature's normal forms of sight rather than replacing it.

Visibility Conditions

These can occur under any light level.

Shadows are areas receiving little direct illumination, such as the space behind pillars, beneath furniture, in deep alcoves, or at the edge of a light source. Shadows are not a separate light level, but represent locations where concealment is possible despite nearby illumination.

Glare occurs when an exceptionally bright light overwhelms the eyes, making nearby details difficult to distinguish. Direct sunlight, polished mirrors, magical radiance, or intense reflections from water, snow, or ice may produce glare at the referee's discretion.

Smoke scatters and absorbs light, reducing visibility even in brightly illuminated areas. Thin smoke obscures distant objects, while thick smoke may reduce visibility to only a few feet or create conditions equivalent to darkness.

Fog and mist diffuse light, making distant objects appear indistinct or disappear altogether. Even under bright illumination, visibility may be severely limited by dense banks of fog.

Dust, ash, and blowing sand fill the air with countless suspended particles that obscure vision and soften detail. Dense clouds may reduce visibility dramatically until they settle or disperse.

Heavy rainfall reduces visibility by masking distant objects behind a curtain of falling water. Wind-driven rain may further limit sight and make identifying creatures or landmarks difficult.

Dense vegetation (e.g., hanging vines, dense hedges, and closely packed trees0 blocks lines of sight regardless of the available light. Creatures may remain partially or completely obscured behind vegetation even in broad daylight.

Heat distortion (e.g., intense heat from lava, roaring fires, furnaces, or similar sources) creates shimmering air and overpowering thermal radiation. Such conditions may make distant objects difficult to discern and greatly reduce or negate the usefulness of infravision.

Extreme cold reduces temperature differences between surrounding objects, diminishing the contrast upon which infravision depends. Although warm creatures remain visible, subtle heat signatures and environmental details become more difficult to distinguish.

Magical darkness suppresses and absorbs light beyond natural means, creating an area of supernatural blackness. Unless an ability or spell specifically states otherwise, creatures relying on ordinary vision—and often even extraordinary vision—cannot see within it.

A NOTE FOR THE DM: This information is intended to shape exploration, not to impose layers of modifiers. Rather than worrying about precise mechanical penalties, consider what the characters could reasonably perceive under the available illumination. Bright light reveals the world clearly, while dim and low light obscure details, create uncertainty, and leave room for surprise. For example, in lower lighting conditions, describe silhouettes instead of identities, movement instead of certainty, and vague shapes instead of obvious dangers. Used in this manner, light becomes more than a measurement—it becomes a tool for building tension, atmosphere, and prompting meaningful player decisions.