Darkness and Light

[MillerHero]

Initially I tried to create one diagram for all possible lighting locations, but it was less cluttered dividing them into four separate diagrams.
Outside direct sunlight
Under forest canopy
Outside moonlight or starlight
Underground or cloudy moonless night

Here is the information I used to create these diagrams.
Five lighting conditions:

• Bright light (BL): outside in direct sunshine
  
• Normal light (NL): underneath a forest canopy during the day
  
• Dim light (DL): outside at night with a moon in the sky, bright starlight
  
• Darkness (DN): unlit dungeon chamber, most caverns, and outside on a cloudy, moonless night
  
• Supernatural darkness (Su): This functions like darkness, but even creatures with darkvision cannot see within the spell's confines.

Methods to increase and decrease illumination levels:

• A torch sheds normal light in a 20-foot radius and increases the light level by one step for an additional 20 feet beyond that area (darkness becomes dim light and dim light becomes normal light). A torch does not increase the light level in normal light or bright light.
• Light and continual flame are equivalent in brightness to a torch.
  
• A daylight spell sheds bright light in a 60-foot radius and increases the light level for an additional 60 feet by one step. Daylight brought into an area of magical darkness (or vice versa) is temporarily negated, so that the otherwise prevailing light conditions exist in the overlapping areas of effect.
• The darkness spell causes an object to radiate darkness out to a 20-foot radius. This darkness causes the illumination level in the area to drop one step, from bright light to normal light, from normal light to dim light, or from dim light to darkness. This spell has no effect in an area that is already dark. Nonmagical sources of light, such as torches and lanterns, do not increase the light level in an area of darkness. Magical light sources only increase the light level in an area if they are of a higher spell level than darkness (2nd). This spell does not stack with itself.
• The spell, deeper darkness, functions as darkness, except that objects radiate darkness in a 60-foot radius and the light level is lowered by two steps. Bright light becomes dim light and normal light becomes darkness. Areas of dim light and darkness become supernaturally dark. This functions like darkness, but even creatures with darkvision cannot see within the spell's confines. This spell does not stack with itself.

Assumptions:

• Ignore low-light vision.
  
• All spells are already in effect and brought to within overlapping areas of each other. No countering or dispelling is occurring.
  
• Since deeper darkness states that it "functions as darkness," and since both deeper darkness and darkness state that "This spell does not stack with itself" I assume that deeper darkness does not stack with darkness.
  
• Conversely, torches and light spells stack with themselves and other spells (up to stated limits). Though the darkness spells have the not-stacking-with-itself clause, the light spells do not have such a clause.
  
• The magical darkness stated in the daylight spell description refers to any darkness created by magic, not just the supernaturally dark area created by deeper darkness within dim light or darkness. Therefore, daylight (3rd) brought into an area of darkness (2nd) negates both spells and the prevailing light conditions exist in the overlapping areas of effect.
  
• The negating power of daylight only functions within the center 60-foot radius – not the additional 60 feet illumination increasing outer ring given that "Creatures that take penalties in bright light take them while within the 60-foot radius of this magical light."
  
• Even though darkness has the clause "This spell has no effect in an area that is already dark." it can still be cast in an area that is already dark and brought into an illuminated area, thus dropping the illumination level one step.
  
• Similarly though a torch (and therefore light and continual flame) does not increase the light level in normal light or bright light, it can be lit (or cast) in normal or bright light and brought into darkness or dimly lit areas and still increase the illumination level by one step within the additional 20-foot outer ring.
  
• Under the same lighting and darkening conditions, the center of a light source is never at a lower illumination level than its own outer ring of increase-the-light-level.
  Example:

  Underneath forest canopy, deeper darkness, 30 feet from the center of a heightened continual flame (4th), 70 feet from the center of a daylight spell. Normal light under the canopy drops two steps from deeper darkness and increases one step from 30-feet-away heightened continual flame (4th) and one step from 70-feet-away daylight for a total amount of illumination equal to normal light. Move to within 10 feet of the center of the heightened continual flame (4th) and keep everything else the same. Normal light under the canopy (and normal light from the heightened continual flame (4th) gets reduced two steps from deeper darkness and is increased one step from 70-feet-away daylight for a total of amount of illumination equal to dim light. It doesn't make sense that the center of a continual flame spell would be dimmer than 30 feet away under otherwise identical lighting conditions. This problem arises from the stated rule that a torch sheds normal light in a 20-foot radius, but doesn't specifically state how many steps it raises the light level within that first 20 feet.
• Increases and decreases in illumination levels are applied in a way so as to not truncate up against the illumination limits (bright light and supernaturally dark).
  Example:

  Underground, deeper darkness, 30 feet from the center of a heightened continual flame (4th), 110 feet from the center of a daylight spell. Deeper darkness drops illumination levels 2 steps, but when applied to the naturally dark underground it creates a supernaturally dark area. Then apply the one step increase of the 30-foot-away heightened continual flame (4th) and the one step increase from the 110-feet-away daylight spell. Does that bring it up to dim light? No, in this example the diagrams take the naturally dark area and apply the light spells first (+2) then apply the darkening (-2) for a result of regular darkness. The opposite case occurs in direct sunshine at the same location between the three spells. If the light spells are applied first to bright light, they have no effect. Apply deeper darkness and the illumination drops 2 levels to dim light. Apply deeper darkness first (-2) then the light spells (+2) and the light remains bright light.

Possible additions to the diagrams:

• Low-light vision.
  
• Show how darkvision penetrates darkness but not supernatural darkness.
  
• Add a torch or lower than 3rd level light spell to the area where daylight overlaps darkness spells to raise the question "Does the 'negate nonmagical sources of light' power of darkness still function even when daylight is overlapping it?
  
• Hatching or shading the different areas of illumination rather than just labeling

Additional questions to consider:
Do two daylight spells stack? If encountering magical darkness, are they both negated?

When talking about lighting conditions please remember to make a distinction between darkness and darkness.

[Komoda]

That looks like a lot of work!

Sorry to have to be the one to point this out, but torches (and all the spells that act like torches) do not increase light any brighter than normal light.

As such, the first circle from the left in the Outside moonlight... graphic is incorrect.

I can't seem to decipher what the difference between a solid line and a dashed line is. Sometimes it appears that one is the effect of the light and the other is the secondary effect of the light, but I can't really tell as other times it seems to change.

What if you used hatching to identify the final result rather that abbreviations? I think it might make more sense.

Great start!

[MillerHero]

Thanks Komoda,
the first circle from the left in the Outside moonlight graphic is for torches, light, continual flame, everburning torches, and ioun torches. It shows the effects of those items/spells on dim light (DL). When they overlap with the 'increases the light level for an additional 60 feet' area of a daylight spell, the normal light is increased to bright light.

The dashed line indicates that there is a difference between two areas, usually spell area versus 'increase the light level' area, but that both areas have the same final light level.

[MillerHero]

According to this blog post darkness's ability to negate non magical sources of light does not work when daylight negates the darkness. Therefore these diagrams are not valid.