From: hall@bcstec.ca.boeing.com (Robert J. Hall)
Newsgroups: rec.games.frp.misc
Subject: Illumination in RPGs
Keywords: Light - Ambient - Point Source - Activities
Date: 2 Oct 92 15:00:53 GMT
Organization: Boeing Computer Services, Seattle


  As promised some time back, here's one possible method for dealing
with light in a role-playing game. I chose to define the data in terms
of GURPS from SJG, but it shouldn't be too hard to convert to other
systems. (Disclaimer: I'm not affiliated with Steve Jackson Games in
any manner. This is not an 'official' GURPS release.)


                  ----------------------------------
                  ILLUMINATION IN ROLE-PLAYING GAMES
                  ----------------------------------

  The following procedure allows a GM to determine the illumination at
a location, as well as the types of activities that can be performed.
For game purposes, there are two types of light sources: Ambient and
Point Source. Inside an area with the same ambient light level, all
light-dependent activities have the same restrictions. A point source,
however, is range dependent and the total lighting is always higher
than the ambient level. However, to simplify the calculation, use the
greater of the ambient and point light intensities to compute the actual
intensity.

 Table 1. Illumination from various ambient lighting sources

  AMBIENT LIGHT CONDITION     LIGHT LEVEL
  -----------------------     -----------
  Night Sky                       -8
  Dim Interior                    -4
  Full Moonlight                  +2
  Twilight                        +5
  Heavy Overcast Daylight         +8
  Office Building                 +9
  Sunlight at Meridian           +11
  Snow in Sunlight               +13

  The following table shows the intensity of various point light sources.
The illumination at a specific distance from a point light source is
determined by adding the Speed/Range modifier from the 'Size and Speed/
Range Table' in the GURPS Basic Set, third edition.

 Table 2. Illumination from various point light sources

  POINT LIGHT SOURCE          LIGHT LEVEL
  -----------------------     -----------
  Video Display                   +0
  Wax Candle                      +3
  Oil Torch                      (+5)
  Camp Fire                      (+7)
  100 Watt Incandescent Bulb      +9
  6' Florescent Bulb             +11
  140 Watt Sodium Lamp           +12
  1,000 Watt Tungsten Halogen    +13
  MF-Type Flashbulb              +15

  (Values within parentheses are best guesses.)

  An object is visible if the total light reaching an observer, such as
an eye or camera, is beyond a certain minimum threshold level. However,
illumination that is sufficient for detection may not be enough to
distinguish details of the object, or even to separate the object from
the background. Thus, less illumination is required to see an object than
to obtain information about the object.

  Various visual activities can be performed inside a range of light
intensities. If the light is too dim, the eye is unable to distinguish
details. Beyond a certain intensity level, the eye becomes overloaded
by light, and activity becomes too painful to continue. Somewhere
between these two extremes is a comfort zone where the eye performance
is optimum.

 Table 3. Intensity extremes for various human activities

  TASK                        LIGHT LEVEL
  -----------------------     -----------
  Discern Shapes                  (?)
  Discern Colors                 (+4)
  Read a Sign                     +5
  Ordinary Inspection             +6
  Office Work                     +7
  Lip Reading                     +8
  Sewing                          +9
  Watch Assembly                 +10
  Discomfort Level              (+13)
  Blinding Light                  (?)

  (Values within parentheses are best guesses.)

  Trivial Example: A man is sitting in a twilight-illuminated chamber
near a candle trying to assemble a plastic model. This is considered
fine detail work on a par with sewing. The required light intensity is
+9, and the candle has a point source intensity of +3. Twilight has an
intensity level of +5, so the candle is required. The range modifier
must be +6, so he must be within at least 6" of the candle.

  The brightness of an object is dependent on various factors, including
the total light striking the object, the amount of light reflected from
the object towards the observer, the size and shape of the object, and
the distance from the object to the observer. To simplify calculations
for a GM, objects are assumed to be simple white shapes that reflect a
high portion of the total incident light towards the observer. Darker
objects will then receive a negative modified.

 Table 4. Illumination Modifiers for various circumstances

  CIRCUMSTANCE                 MODIFIER
  --------------------------   --------
  Deep Shadows                   (-6)
  Dark Object                    (-4)
  Binoculars                      (?)
  Adjusted to Total Darkness     (+6)
  Night Vision Goggles            (?)

  (Values within parentheses are best guesses.)

  These values were obtained from various scientific and engineering
handbooks, and some photography manuals. Unfortunately, there were
differences in data between some of the sources, so the values were
weighted toward the reference works. Obviously, a lot more data can
be added to these tables, and many of the values can be sharpened up
somewhat. If you have any more entries you can add, please e-mail me
with your data.

  Enjoy!
-- 
 Bob Hall,                 | "If at first you don't succeed, try, try again.
 Workstation Peripheral    | Then give up. No use being a damn fool about it."
 Boeing Computer Services  |                                     -Groucho Marx
Newsgroups: rec.games.frp.misc