Light and Darkness in My Games

Light and Darkness in My Games

Since light and darkness rules in GURPS are very inconsistent, I decided to consolidate rules for my games. Only relevant rules will be present, and none of the rules I do not want to bother with will be present. High-tech light sources are removed. A new illumination levels table is made, combining some parts of the tables from GURPS Powers: Enhanced Senses (v1.1) and GURPS Template Toolkit 2: Races. I left the Minimum Lux column to differentiate between the different “0” light levels, as this may come up with light spread rules for very powerful light sources.

 

Illumination Levels
Penalty	Minimum Lux	Natural Light	Artificial Light
-10	0	Total darkness	Total darkness
-9	0.0001	Overcast moonless night	-
-8	0.0005	Starlight through clouds	-
-7	0.002	Starlight, luminescent fungi	-
-6	0.01	Quarter moon*	-
-5	0.05	Half-moon*	Luminous dust
-4	0.2	Full moon*	Candle†
-3	1	Deep twilight*	Ring of illumination
-2	5	Twilight*	Fire beetle lamp†, glow vial, glowbug bloodspike, hearthfire†, oil lamp†, torch†
-1	20	Sunrise or sunset	Bull's-eye lantern, covered lantern, helmet lamp, sunrod
0	100	Very overcast day	Burning stone, daylight pellet, lantern with farflame oil†, liquid sunlight, ring of golden illumination
0	500		-
0	2,000		-
0	10,000	Daylight	-
0	50,000	Direct sunlight	-
+3 levels	x100		-
* Assumes a clear sky; apply another -1 for heavy clouds. Above the Arctic Circle or below the Antarctic, moonlight is weaker; add another -1. † This includes a -1 penalty for flickering.

 
Flickering lights or moving shadows can add another ‑1 to ‑3.

Water strongly diminishes the intensity of visible light; reduce illumination by one level per 50 yards of depth.
The light source is a single, nearby point. The listed modifier assumes one yard of distance from this. At two yards, apply another ‑1. At greater distances, add half the range penalty (p. B550), rounded for the worse, to this ‑1; e.g., a candle gives ‑3 at one yard, ‑4 out to two yards, ‑5 out to five yards, ‑6 out to 10 yards, and so on. Stop once the penalty reaches the area’s ambient illumination level – a light source will never make things darker!
A light source in a dark environment eliminates or reduces Vision penalties within the illuminated area. Treat the light as “in plain sight” to distant observers who have a clear view of it: +10 to Vision rolls to notice the lighted area (p. B358).
The total of all penalties mentioned here – for darkness, shadows, inadequate equipment, flickering, etc. – has a floor of ‑10. If the total is worse, treat it as ‑10.
 
Darkness penalties apply to Vision rolls, DX-based rolls that rely on vision, including attack rolls. Parry and Block take halved penalties, rounded for the best. Dodge takes quartered penalties, rounded for the best. Thus, darkness -5 would impose a -2 penalty to Parry and Block, and a -1 penalty to Dodge.
 
    Now, let’s list which prices and values are “canon” for my games, as light sources are inconsistent in the published books.
    The following ones are used from GURPS Low-Tech as is, including the rules for handling:
-          Oil Lamp
-          Torch
-          Candle
-          Covered Lantern
Here are some other light sources with some additional notes:
-          Bull’s-Eye Lantern (GURPS Dungeon Fantasy 1: Adventurers, p. 26). This is a TL3 item.
-          Burning Stone* (GURPS Dungeon Fantasy 8: Treasure Tables, p. 23). This is a TL3 item.
-          Daylight Pellet*.
-          Farflame Oil. This item is compatible with any oil lamps or lanterns. For beam lanterns, such as the helmet lamp and bull’s-eye lantern, it doubles the length of the beam. For area lanterns, such as the oil lamp, it improves the illumination level, as shown on the table.
-          Fast Torch*. Treat as a normal torch for the purpose of illumination.
-          Fire Beetle Lamp*.
-          Glow Vial*.
-          Glowbug Bloodspike*.
-          Hearthfire*.
-          Helmet Lamp (GURPS Dungeon Fantasy 1: Adventurers, p. 25). This is a TL3 item.
-          Liquid Sunlight*.
-          Luminous Dust*.
-          Ring of Golden Illumination*.
-          Ring of Illumination*.
-          Signal Torch*. Treat as a normal torch for the purpose of illumination.
-          Sunrod*.
* The light rules here override the description, unless you are using the simplified DF illumination rules.