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Part I is written primarily from the point of view of a human being with 20/20 sight. Pt. II will address people from different biospheres and demi-humans, and Pt. III Wildlife. Later treatments will address aquatic life and monsters.
Weather Conditions
Standard weather forecasting tools are readily available to define common visibility benchmarks.
In other words, in Clear weather and with sufficient light and elevation, one can easily see major features like a mountain across two standard D&D BECMI 8-mile hexes. A human observer with 20/20 vision can perceive a man-sized object as a tiny dot up to about 2 to 3 kilometers (1.2 to 1.8 miles). With a spyglass, one can identify a cavalry banner 4 miles away, spot a man-sized object about 8 miles away, enemy troop movement 16 miles away, and a large galleon 28 miles away (with enough elevation to overcome Earth’s curvature, like from a skyship). Curvature otherwise blocks ground objects from view after 3 miles.
Distances listed in this article are approximated for simplicity. The DM can adjust them as needed. Factoring in weather and air quality, reduce these distances by the same proportion. Very roughly, halve distances with Moderate conditions, divide them by 5 for Low, and by 10 for Poor/Hazardous.
Other Details
Visual ranges determine what level of detail is visible, as listed below. Multiply the distances below by about 5 with a spyglass.
The Trouble with Spyglasses
Early optical devices are more vulnerable to weather conditions and other factors than the naked eye. High humidity or rapid temperature changes cause condensation inside the spyglass. Rain or sea spray can cover the outside lens. High heat causes the image to ripple, warp, and shimmer like water. Twilight or heavy overcast renders the spyglass useless because too little light enters its narrow tube to create an image the eye can perceive. If subject to movement (riding a horse, standing on a ship’s deck in rough seas, or on a skyship in high winds), the spyglass's narrow field of view can’t be aligned with the target; the image inside the tube quickly shifts and jitters, entirely defeating the spyglass’s purpose and causing motion sickness to its user. In Low or Poor/Hazardous weather conditions, the spyglass is mostly useless.
Ambient Light
The lower the ambient light, the shorter the visual range. For simplicity, apply the following rules of thumb. In full daylight, use the ranges listed earlier. To perceive a man-sized object in overcast conditions, roughly halve the visual range; at twilight or dusk, divide the distance by 5; in full moonlight, by 30; under starlight only, by 150. The chart below gives relative ranges.
By twilight, red and yellow begin to look like black or dark gray. Under full moonlight, everything turns shades of silvery-gray. In heavy mist, cool colors (blues, purples, greens) wash out and fade into white or gray; warm colors (reds and ambers) can pierce through fog slightly better. With wildfire smoke or in a dust storm, entire landscapes take on a monochromatic amber or crimson tint.
Backlighting or Silhouetting
If a light source behind an object is powerful enough to be seen from a distance, the human eye can easily detect the object’s geometric "break" in that light, even more so if it moves.
Under clear, pitch-black conditions, a night-adapted human eye can spot the glowing tip of a smoldering cigarette up to 100 to 150 meters (330 to 500 feet). When a smoker takes a "drag" or lights a match, the hotter flare intensifies the light output, allowing a human observer to spot the glow from up to 500 meters (about 0.3 miles) away. Under the same conditions, a burning torch can be spotted from 4 to 6 kilometers (2.5 to 3.7 miles); an oil lantern from roughly 2.5 to 4 kilometers (1.5 to 2.5 miles).
A human observer can see a 30-foot-radius D&D light spell from 6.5 to 9.5 kilometers (4 to 6 miles) away, while aerial predators (eagles, griffons) can spot it from more than 10 miles away. Underground, such a spell is like setting off a flashbang in the eyes of Underdark creatures (dwarves, orcs, goblins, dark elves). A human observer on a high vantage point could observe a 40-foot-diameter fireball (and fireworks in general) from 48 to 64 kilometers (30 to 40 miles) away. Even with hills blocking direct line of sight to the area of effect, the spell’s glow can be spotted in the sky from dozens of miles away. A fireball would likely blind nocturnal animals looking directly at the area of effect from a few hundred yards away while the spell flares. Stranger things are also visible in the dead of night, as follows:
Vision Underwater
Water severely restricts visual distances, even while wearing a diver’s mask, as follows:
At 10 meters (33 ft), ambient light drops to 15% of surface light, making the aquatic environment look predominantly blue-green. At 40 meters (130 ft), darkness reigns with 1.5% of surface light filtering through. This directly affects the distances listed in the above chart. Waters in caves require artificial light. In a pool of pristine water at shallow depth under surface daylight, horizontal visibility while wearing goggles ranges between 50 and 60 meters (164 to 196 feet).
Red disappears completely at just 5 meters (15 feet) deep, turning dark brown or black. Orange fades at 20 meters, and yellow vanishes by 50 meters. At lower depths, the only color that can be identified is deep violet-blue, meaning any creature without aquatic eyes sees a completely blue-monochrome world.
A masked observer in pitch-black conditions can perceive a 30-foot-radius D&D light spell from 120 to 180 meters (400 to 600 feet) away in clear water. If the same spell is cast in a lake, river, or coastal sea, natural turbidity drops the visual range to a mere 5 to 15 meters (16 to 50 feet).
Within the area of effect, the caster can clearly see immediate surroundings. The light spell’s color, however, may create a twilight-like halo around the area of effect as wide as 30 feet, allowing some perception outside the spell’s limit, as listed in the chart below. On the other hand, the most efficient color piercing through water also makes it more visible to outside observers.
Wikipedia states the following: “A diver's distance judgment is warped. At close range in clear water, magnification makes things look about 25% closer than they are. As things move farther away, the water's natural cloudiness (turbidity) destroys contrast, causing the brain to overcompensate and perceive a distant silhouette as much farther away than it actually is.” Sea elves and aquatic monsters are immune to this effect.
Weather Conditions
Standard weather forecasting tools are readily available to define common visibility benchmarks.
In other words, in Clear weather and with sufficient light and elevation, one can easily see major features like a mountain across two standard D&D BECMI 8-mile hexes. A human observer with 20/20 vision can perceive a man-sized object as a tiny dot up to about 2 to 3 kilometers (1.2 to 1.8 miles). With a spyglass, one can identify a cavalry banner 4 miles away, spot a man-sized object about 8 miles away, enemy troop movement 16 miles away, and a large galleon 28 miles away (with enough elevation to overcome Earth’s curvature, like from a skyship). Curvature otherwise blocks ground objects from view after 3 miles.
Distances listed in this article are approximated for simplicity. The DM can adjust them as needed. Factoring in weather and air quality, reduce these distances by the same proportion. Very roughly, halve distances with Moderate conditions, divide them by 5 for Low, and by 10 for Poor/Hazardous.
Other Details
Visual ranges determine what level of detail is visible, as listed below. Multiply the distances below by about 5 with a spyglass.
The Trouble with Spyglasses
Early optical devices are more vulnerable to weather conditions and other factors than the naked eye. High humidity or rapid temperature changes cause condensation inside the spyglass. Rain or sea spray can cover the outside lens. High heat causes the image to ripple, warp, and shimmer like water. Twilight or heavy overcast renders the spyglass useless because too little light enters its narrow tube to create an image the eye can perceive. If subject to movement (riding a horse, standing on a ship’s deck in rough seas, or on a skyship in high winds), the spyglass's narrow field of view can’t be aligned with the target; the image inside the tube quickly shifts and jitters, entirely defeating the spyglass’s purpose and causing motion sickness to its user. In Low or Poor/Hazardous weather conditions, the spyglass is mostly useless.
Ambient Light
The lower the ambient light, the shorter the visual range. For simplicity, apply the following rules of thumb. In full daylight, use the ranges listed earlier. To perceive a man-sized object in overcast conditions, roughly halve the visual range; at twilight or dusk, divide the distance by 5; in full moonlight, by 30; under starlight only, by 150. The chart below gives relative ranges.
By twilight, red and yellow begin to look like black or dark gray. Under full moonlight, everything turns shades of silvery-gray. In heavy mist, cool colors (blues, purples, greens) wash out and fade into white or gray; warm colors (reds and ambers) can pierce through fog slightly better. With wildfire smoke or in a dust storm, entire landscapes take on a monochromatic amber or crimson tint.
Backlighting or Silhouetting
If a light source behind an object is powerful enough to be seen from a distance, the human eye can easily detect the object’s geometric "break" in that light, even more so if it moves.
Under clear, pitch-black conditions, a night-adapted human eye can spot the glowing tip of a smoldering cigarette up to 100 to 150 meters (330 to 500 feet). When a smoker takes a "drag" or lights a match, the hotter flare intensifies the light output, allowing a human observer to spot the glow from up to 500 meters (about 0.3 miles) away. Under the same conditions, a burning torch can be spotted from 4 to 6 kilometers (2.5 to 3.7 miles); an oil lantern from roughly 2.5 to 4 kilometers (1.5 to 2.5 miles).
A human observer can see a 30-foot-radius D&D light spell from 6.5 to 9.5 kilometers (4 to 6 miles) away, while aerial predators (eagles, griffons) can spot it from more than 10 miles away. Underground, such a spell is like setting off a flashbang in the eyes of Underdark creatures (dwarves, orcs, goblins, dark elves). A human observer on a high vantage point could observe a 40-foot-diameter fireball (and fireworks in general) from 48 to 64 kilometers (30 to 40 miles) away. Even with hills blocking direct line of sight to the area of effect, the spell’s glow can be spotted in the sky from dozens of miles away. A fireball would likely blind nocturnal animals looking directly at the area of effect from a few hundred yards away while the spell flares. Stranger things are also visible in the dead of night, as follows:
Vision Underwater
Water severely restricts visual distances, even while wearing a diver’s mask, as follows:
At 10 meters (33 ft), ambient light drops to 15% of surface light, making the aquatic environment look predominantly blue-green. At 40 meters (130 ft), darkness reigns with 1.5% of surface light filtering through. This directly affects the distances listed in the above chart. Waters in caves require artificial light. In a pool of pristine water at shallow depth under surface daylight, horizontal visibility while wearing goggles ranges between 50 and 60 meters (164 to 196 feet).
Red disappears completely at just 5 meters (15 feet) deep, turning dark brown or black. Orange fades at 20 meters, and yellow vanishes by 50 meters. At lower depths, the only color that can be identified is deep violet-blue, meaning any creature without aquatic eyes sees a completely blue-monochrome world.
A masked observer in pitch-black conditions can perceive a 30-foot-radius D&D light spell from 120 to 180 meters (400 to 600 feet) away in clear water. If the same spell is cast in a lake, river, or coastal sea, natural turbidity drops the visual range to a mere 5 to 15 meters (16 to 50 feet).
Within the area of effect, the caster can clearly see immediate surroundings. The light spell’s color, however, may create a twilight-like halo around the area of effect as wide as 30 feet, allowing some perception outside the spell’s limit, as listed in the chart below. On the other hand, the most efficient color piercing through water also makes it more visible to outside observers.
Wikipedia states the following: “A diver's distance judgment is warped. At close range in clear water, magnification makes things look about 25% closer than they are. As things move farther away, the water's natural cloudiness (turbidity) destroys contrast, causing the brain to overcompensate and perceive a distant silhouette as much farther away than it actually is.” Sea elves and aquatic monsters are immune to this effect.
---
That’s it for environmental conditions. Parts II and III will compare
the visual acuity of people and animals, and how their sight has
adapted to their natural worlds. Until then, keep your eyes peeled. Wink,
wink...
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