Chapter 3: Place
3.7. Lighting

At any place (room, or inside a container) light is either fully present or fully absent. Inform does not usually try to track intermediate states of lighting, but see The Undertomb 2 for a single lantern with varying light levels and Zorn of Zorna for multiple candles that can be lit for cumulative changes to the light level.

Light can be added to, but not taken away: rooms and things can act as sources of light, by having the "lighted" and "lit" properties respectively, but they cannot be sinks which drain light away. The reason darkness is not a constant hazard in Inform-written games is that rooms always have the "lighted" property unless declared "dark". (We assume daylight or some always-on electric lighting.) A "dark" room may well still be illuminated if a light source happens to be present:

The Deep Crypt is a dark room. The candle lantern is a lit thing in the Deep Crypt.

Hymenaeus allows us to explicitly refer to torches as "lit" or "unlit", or (as synonyms) "flaming" or "extinguished".

For light produced electrically we might want a wall switch, as in Down Below, or a portable lamp, as in The Dark Ages Revisited.

The fierce, locally confined light thrown out by a carried lamp has a quality quite unlike weak but ambient daylight, and Reflections exploits this to make a lantern feel more realistic.

When the player experiences darkness in a location, Inform is usually very guarded in what it reveals. ("It is pitch dark, and you can't see a thing.") Hohmann Transfer gives darkness a quite different look, and Four Stars heightens the other senses so that a player in darkness can still detect her surroundings. The first of the two examples in Peeled allows exploration of a dark place by touch.

It is sometimes useful to check whether a room that is not the current location happens to contain a light source or be naturally lighted. This poses a few challenges. Unblinking demonstrates one way of doing this, so long as there are no backdrop light sources.

Cloak of Darkness is a short and sweet game based on a light puzzle.

* See Room Descriptions for an item that can only be seen in bright light, when an extra lamp is switched on

* See Looking Under and Hiding for a looking under action which is helped by the fiercer brightness of a light source

* See Going, Pushing Things in Directions for making it hazardous to walk around in the dark

* See Electricity and Magnetism for batteries to power a torch or flashlight

* See Fire for a non-electrical way to produce light


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** Example  The Undertomb 2
Flickering lantern-light effects added to the Undertomb.

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*** Example  Zorn of Zorna
Light levels vary depending on the number of candles the player has lit, and this determines whether or not he is able to examine detailed objects successfully.

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* Example  Hymenaeus
Understanding "flaming torch" and "extinguished torch" to refer to torches when lit and unlit.

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** Example  Down Below
A light switch which makes the room it is in dark or light.

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* Example  The Dark Ages Revisited
An electric light kind of device which becomes lit when switched on and dark when switched off.

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* Example  Reflections
Emphasizing the reflective quality of shiny objects whenever they are described in the presence of the torch.

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** Example  Hohmann Transfer
Changing the way dark rooms are described to avoid the standard Inform phrasing.

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Inform automatically keeps track of light and darkness, handling such questions as whether a room is lit, whether the player can see any light sources, etc., and then managing the descriptions accordingly. When the room is dark and no light sources are visible, the player is said to be "in darkness".

If we don't specify otherwise, Inform will describe our surroundings in a dark room thus:

Darkness
It is pitch dark, and you can't see a thing.

This is fine in many situations, but we may sometimes want to replace this phrase with something else.

"Hohmann Transfer"

The Western Hemisphere is a dark room. "The cloud mass covers much of the land on this side of the planet, and a particularly nasty storm is brewing off to the south."

The Eastern Hemisphere is west of the Western Hemisphere. The Eastern Hemisphere is east of the Western Hemisphere. The Eastern Hemisphere is north of the Western Hemisphere. The Eastern Hemisphere is south of the Western Hemisphere. "This side of the planet is more ocean than land, with only two continents worthy of the name, and a volcanic archipelago in the north seas."

Use full-length room descriptions.

Rule for printing the description of a dark room:
    say "It's night on this side of the planet, so you can make out only the glow of urbanized areas along the seacoasts." instead.

Rule for printing the name of a dark room:
    say "Dark Side" instead.

And now a few minor refinements so that we can see what happens when one room becomes dark and the other light:

Carry out going:
    say "You fire the thrusters and loop around to the other side of the planet before settling into a new geosynchronous orbit. Six months and one minute later..."

The time of day is 4:55 PM.

At 5 PM:
    now the Eastern Hemisphere is dark;
    now the Western Hemisphere is lit.

Rule for printing the announcement of darkness:
    say "The planet abruptly spins itself over, exposing its cool underbelly to the sun."

Test me with "e / z / z / w / z / z / e".

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*** Example  Four Stars 1
An elaboration of the idea that when light is absent, the player should be given a description of what he can smell and hear, instead.

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* Example  Peeled
Two different approaches to adjusting what the player can interact with, compared.

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*** Example  Unblinking
Finding a best route through light-filled rooms only, leaving aside any that might be dark.

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**** Example  Cloak of Darkness
Implementation of "Cloak of Darkness", a simple example game that for years has been used to demonstrate the features of IF languages.

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