As a rule if something burns, it produces heat and will set flammable things it is touched against alight.  Another pointer that something is incendiary is if it consumes fuel, and burns out after a time.  So for example if a gas floating above a swamp, burns with an eerie light for 4 hours, then the gas is incendiary, not a glowing source.  

Bright or very bright objects are nearly always incendiary.  This is true for magical fires, alchemical fires and natural wood or other fires.  

The lantern is a special case - it is incendiary, but the flame is shielded by a metal and glass surround preventing it from touching against flammable items.  If a flammable item somehow gets past the surround it will burn however - leaking gas in a dungeon, for example.

Sparks may be struck from a flint and steel and this will set flammable objects alight.

Any spell or effect that does damage, where the rules for damaging objects can be applied, and the fire keyword applies, is also incendiary.

Lighting your Way

The portable light sources listed all allow for being held in a characters hand.  Generally when adventuring in dim lighting or darkness the light source is held up to light the way ahead, in the direction the character is looking.  The character must have a free hand for this. 

If they are grabbing in combat, or weilding weapons and/or a shield such that both hands are used then the character should specify what they are doing with their light source.

If the light source is not held, then for sources which are non-incendiary they can be placed into a backpack or tucked into a belt or strap.  When stowed the light source no longer lights your way.  It may produce some random illumination at the DM's discretion, but it is not in generall lighting the direction a player is looking.

Alternatively light sources may be placed on the ground or any other flat surface where they continue to shed light in the radius as determined by the rules (see the table above).  Obviously if a light source is placed on the ground it does not follow the character during movement.

Lighting and Lines of Vision

Generally light is simple and can be assumed to evenly light all areas in a room.  In dungeons lit by torches (magical or otherwise) fixed to the walls, this is the case.  Generally its assumed that an area has such "ambient lighting".

If most characters are carrying light sources, and looking around as normally alert characters would do by lighting their own way then again its equivalent to all areas in the room being evenly lit.

If a character is carrying a portable light source, then in reality, since light travels in straight lines, things (including objects, creatures and features of the setting) which are behind cover are not lit by that light source.  However if trying to see a creature to attack it, then the normal rules of cover, on Pg 280 of the PHB apply.  There is no extra penalty for it not being properly lit.


Cover from lighting does apply in situations where something is the target of a characters skill or ability check.  if a character is trying to understand an inscription, or detect a trap then the rules for cover on Pg 280 of the PHB apply.  Treat the light as the "attacker" and the thing being looked at as the "target".  If the target has cover then take a -2 to any skill checks involved - History or Dungeoneering to read an inscription, Thievery to detect a trap.  If the target has superior cover then take a -5 to any skill check involved.  This rule would only take effect if something prevented the characters moving their light source so that it illuminated the target - for example an area of traps.  The DM is free to ignore this effect for simplicity.

Hiding in Dark Corners

If characters are exploring a dungeon, or walking around an unfamiliar building, then dark unlit areas abound - until light is shone into them by the characters lantern or torch.

If a character for whatever reason is not carrying a light source, but there is a light source somewhere in the room - ie the room is not evenly lit - then these dark corners can conceal surprises for the characters.  These are cases where none of the conditions exist as described in the basic rule for lighting above.

This applies for example if a dungeon is being explored and the player characters have tossed a lit sun rod into the centre of the room, but do not carry their own light sources.  The sunrod lights for 100 feet in all directions, but behind obstacles there are patches of darkness..  If there is a large pillar occupying a square near the edge of the room a creature, or some other surprise may have cover from the light and thus be hidden from view.

Ultimately it is the DM who provides the information of what the characters see.  Perhaps the area is such that even though a single point light source is used, the reflected light from the walls fills the space, creating ambient light.

The DM may indicate if some part of the map is currently in dim light or darkness, given the current arrangement of lights. 

But players should take responsibility also for lighting their way, and be aware that if an area has cover from light sources it may conceal something: a monster, trap or anything at all that is small enough to fit in the dark area.

Just because an area which is in darkness appears empty on the map does not mean it is empty: a monster or other surprise may be lurking there if the area is in darkness.

The diagram below shows an obstacle, the marble column, blocking the light source and producing an area of shadow.  Notice that if the light source is a torch, then the bugbear would be in darkness anyway since the torches radius is 5 squares.  If the light source is a lantern the DM may well decide that the light casts a shadow as shown in the diagram, and a creature may hide there.  If the light source is a sunrod, and the area shown is surrounded by walls, the DM may rule that there is sufficient reflected light, and thus no shadow exists.




Note that many spells, particularly warlock spells, and some monster spells like the shada-kai's "Deep Shadow" produce an effect of a "thick darkness", "thick poisonous haze" and so on.  Despite any wording, these effects behave like obscuring terrain, discussed in the next section.  In other words, they block or partly block vision.

Normal unlit areas, that is actual shadows, need to be distinguished from magical effects that have the keyword shadow in their name.  Normal shadows do not block lines of vision.

Normal dark areas or shadows result from squares having cover from a light source.  Creatures in the area of darkness cannot be seen, but creatures brightly lit - even if an area of darkness intervenes - can be seen.  In summary, normal areas of darkness do not provide any obscuring effect.

See the diagram above which illustrates this - the attacking ranger in the bottom left of the picture can target the brightly lit bugbear in the bottom right of the picture.  However the bugbear in the shadow of the column has cover from the light source and is thus in darkness.  The attacking ranger does not have dark-vision and thus the bugbear has total concealment.

In the case of the shada-kai witches "Deep Shadow" aura however, it behaves like obscuring terrain and the bugbear at the top of the picture thus has cover (at least one line of sight is blocked).

Obscuring Terrain

A square that is filled with smoke, mist or some other substance that prevents clear vision is obscuring terrain.  Obscuring terrain is like blocking terrain in that it gives cover from view to anything in or behind it.

• Lightly obscured - foliage, fog, smoke and heavy snow/rain
• target in or having cover by a lightly obscured square has concealment (-2 to hit)
• see "Basic rule for Vision & Dim Lighting" below
  
• Heavily obscured - very thick foliage, very thick fog, very thick smoke
• target in or having cover by a heavily obscured square has total concealment (-5 to hit)
• see "Basic rule for Vision & Darkness" below 
• if the attacker is adjacent to the target, the target only has concealment, not total concealment
• Totally obscured - darkness like a black wall, caused by some magical effects
• target in or having cover by a heavily obscured square has total concealment (-5 to hit)
• see "Basic rule for Vision & Darkness" below
  

The summary is that when it comes to obscuring terrain:

• lightly means the same as dim-light
• heavily means the same as darkness, unless adjacent when it means the same as dim-light
• totally means the same as darkness

Special vision (see the next section) does not generally apply to obscured squares.

Vision

There are 3 kinds of vision creatures (and characters may have)

• Normal vision - take a penalty in dim light, cannot see at all in darkness
  
• Low-light vision - no penalty in dim light, cannot see at all in darkness
  
• Darkvision - no penalty in any light

Notice in particular that creatures and player characters with low-light vision, cannot see at all in darkness.  So its not that they take a penalty, they - just like normal vision characters - cannot see at all.

However, in darkness there are other senses to guide you so all is not lost.  Read on.


Obviously this basic rule does not apply when the attacker has low-light vision - those attackers take no penalty.


Area attacks and close attacks do not take the -2 or -5 penalty to hit.  Attacks which hit based by the square or squares which creatures may occupy do not take this penaly since they sweep across all those squares, and don't require the creature itself to be specifically targetted.

Targetting What you Can't See

The above two basic rules apply if when you can locate the target.  Where a creature has total concealment or is otherwise hidden, first the rules for "Targeting What You Can't See" apply.

These rules have been modified slightly by the PHB errata released by Wizards.  Basically the change in the errata is that the creature attempting to hide makes a stealth check as part of attempting to move in its turn (rather than at the end of its turn).  The rest of the details are left up to the rules for Stealth (Pg 188 PHB and Perception Pg 186 PHB, or Pg 222 PHB2) which cover the situation withouth the need to spell it out in the section on Concealment.



Basically the Stealth rules introduce the concept of being hidden.  A creature may be invisible to an attacker, due to being in darkness, behind cover or any other way of not being seen.  But it is not necessarily hidden, since the attacker may hear it or sense that it is there through some other means.

This means that if a monster is in darkness, the DM may decide that it attempts to hide from the players.  If so, the DM rolls stealth for the creature.  This is not a action - standard or otherwise - its just a check of how stealthy it is whilst it does what ever its doing that turn.  This probably involves movement, since the players will know the last location of the creature, but there are penalties on stealth for moving or making noises.  It takes -5 to its stealth check for moving more than 2 squares, -5 for calling out (eg to warn its allies) and -10 for running.  Typically the creature will move or shift 1 or 2 squares.

Of course player characters can hide in the darkness too - the same roll applies.

If successful then the creature (or character) is hidden from (as well as invisbile to) the attacker.

In game, the DM will just announce that the creature or character is now hidden from whichever attackers it won its stealth check against.  If there is a miniature, then just leave it in place, for ease of play.  At this point the rules for targetting hidden creatures applies.


Area and close attacks on squares that contain the hidden creature do not take this -5 penalty.

In game, the player (or DM if its a monster) attacking the hidden character or creature specifies their attack and which square they are centering their attack on.  For a melee attack the attacker can move up to the chosen square and attack it as tho' it contained the target.

The DM will resolve whether the attack hits the hidden creature, and then damage is awarded normally on a hit.

In the case of a hidden player, it is easier for the player to continue to leave their miniature on the map and count out movement normally. 

However the DM must make sure that DM knowledge is not "monster knowledge".  One way to do this is to use the square guessing rule below.

Monster Square Guessing Rule

When a monster attempts to attack an invisible player, the DM first specifies the monsters attack, which will be directed at some square on the map.

To guess which square an invisible Player Character is in the DM rolls percentile dice.  The target number is 30%.

For each square the Player Character has moved since becoming hidden (even if the movement is not in a straight line) subtract 5%, to a minimum of 5%.

The DM rolls percentile dice under this figure.  On success the monster guesses the correct square.  If the roll fails by less than 10% the monster guesses a random square near enough for an area or close attack to hit. 

On all other rolls the monster guesses some random square which does not contain the player character, and which would not include the player character in an area attack.

The attack takes place on the random square whether the player is in it or not.

Summary of Benefits for being hidden.

The hidden creature:

• gains combat advantage over a target that cannot see it
• cannot be targetted - attacks must instead target a square
• if the square chosen for the attack target contains the hidden creature, the attack is at -5
• close and area attacks already target squares and do not take this penalty

A hidden creature is revealed to an enemy, and loses the above benefits if the hidden creature:

• is seen, ie the enemy creature gains clear line of sight to it
• concealment is enough to remain hidden
  
• total concealment is not required
• draws attention
• by talking above a whisper
• raising a light, or dropping something
• moves more than 2 squares and fails a stealth check:
• with -5 penalty when moving >2 squares
• with -10 penalty when running
• attacks - doing anything that requires an attack roll

Other than this, the creature does not require any stealth roll