Lighting in Unity is more fully featured than ever.

The lighting pipeline includes realtime global illumination,

in addition to traditional baked light mapping techniques.

These combined with physically-based rendering

and the standard shader

give more power and versatility to light more complex scenes.

Unity uses physically-based rendering, or PBR

to create a friendly way of achieving a consistent

plausible look for materials under all lighting conditions.

In order to do so, Unity models how light actually behaves

and follows the laws of physics on how

light interacts with materials.

These materials are usually created using the standard shader.

The standard shader makes physically

based rendering easy and accessible to use.

One of the most powerful tools in the Unity

pipeline is Unity's realtime global illumination,

or GI.

Using GI, all lights in the scene can effect

the object's within range with both

direct and indirect illumination.

Direct illumination comes from lights

shining directly on the objects in the scene.

Indirect illumination however

is the light reflected, or bounced off of

the light surfaces in the scene.

This bounced indirect light

can illuminate nearby objects

mimicking how light behaves in the real world

This indirect light is effected

by the colour of the surfaces it bounces off of,

taking a contribution of that surface's colour with it.

Direct and indirect light will

blend together to create a much more realistic look.

In addition to the default main camera

a new scene in Unity comes with

a default sky box

and a default directional light aligned

with that sky box.

Each scene also contains default

values for ambient light.

Ambient light illuminates all surfaces in the scene.

Ambient light is controlled by the settings in the

lighting panels Environment Lighting tab.

Ambient light can be created by either

using a sky box,

a user generated gradient of 3 colours,

or a single colour.

All objects added to the scene

will receive ambient light

unless the ambient intensity value is set to 0

or the ambient light's colour values are set to black.

It is rare, if not impossible

for any real-world material

to have absolutely no reflectivity.

By default all objects in the scene

will also receive reflection information.

Even though the cube, sphere and plane in the scene

are unlit and ambient light is none

they still receive lighting information

in the form of reflections.

The default reflection source is the sky box.

This can be changed to a custom cube map.

To receive no default reflections

either set the custom cube map to none,

or remove the sky box.

It is worth noting that the default sky box

is procedurally generated

and new procedural sky boxes

can be created and saved as assets.

When lighting scenes in Unity

we can work with realtime lighting,

baked lighting,

or a mixture of both.

Realtime lighting is more easily modified at run time.

but it comes at a cost to performance.

Baked lighting on the other hand pre-calculates

much more detailed lighting information

and saves it to a light mapped texture on disc.

This light map information is then

read from the texture at run time,

avoiding the need to do any lighting

calculations when the project is running.

This saves performance,

but at the cost of dynamic changes in the scene.

Baked light maps are not updated at run time.

Lights can be switched between realtime, baked,

and mixed lighting on a per-light basis.

Using baked lighting exclusively

would be more appropriate for target platforms

such as mobile devices with lower performance capabilities.

The light mapping system can either work

continuously or on demand.

When continuous baking is selected

lighting changes will be baked in the background while editing.

These changes can either be properties

adjusted in the inspector,

or objects changed in the scene.

When continuous baking is not selected

changes will only preview on demand.

When the Build button in the lighting panel has been selected.

In this scene there is a directional light

coming in through the skylight in the ceiling.

This light contributes to the illumination of the entire scene

as the light bounces off of the surfaces

it lights directly,

on to other nearby surfaces in an indirect manner.

This light continues to indirectly

illuminate nearby surfaces

until the strength of the light fades

and it can bounce no more.

Decrease the intensity of the light

and the illumination of the scene decreases accordingly.

Likewise, if the directional light

is rotated to directly light a

different part of the scene,

it will now illuminate the scene in a different way,

with both it's direct and indirect lighting.

As materials created with a standard shader

can mimic a wide variety of physical surfaces

and different materials can have different

amounts of reflectivity

this can effect the scene's lighting.

To help balance this the Bounce Intensity can be adjusted

on either a per-light basis

or globally by adjusting the settings

in the lighting panel.

Adjustments can be made here to artificially

change the potential bounce of light from a lit surface.

Adjust the mount of indirect light

in the scene, and more.

In addition to lights we can use

emissive surfaces to contribute to the scene's lighting.

This scene is lit with a variety of lights

and light types, including emissive surfaces.

Emissive surfaces are a light source,

but they behave very much like indirect bounced light.

The primary emissive surfaces in the scene

are in the main corridor junction.

But additional panels are located throughout the scene.

All of these emissive surfaces use

the standard shader's Emission property

by adjusting the Emissive scale.

The float value next to the Emission property

and by adding a touch of colour,

the mood of our scene changes.

As these lights can participate in realtime light mapping

they can be controlled at runtime using

code or animation to create

complex changes in mood

while our projects are running.

The final contributing factor in lighting

a Unity scene are probes.

There are 2 types of probes in Unity.

Light probes

and reflection probes.

Light probes sample the lighting in the scene

at different positions in the world.

The information in these probes can be used

to light dynamic elements in the scene

such as characters or other moving objects

at a low cost to performance.

Reflection probes on the other hand

act as a single point of reference to

calculate reflections from

Surrounding each reflection probes

is a cuboid that specifies

what should be included in that reflection.

These probes sample the elements surrounding them

using box projection,

and store that information in a cube map.

Materials with reflective surfaces

that are on objects within the reflection probe's volume

can then reference this cube map to

create reflective surfaces.

By default there is one built-in

reflection probe in every scene.

This default reflection probe

reflects the sky box to create basic reflections.

For more detail in the reflections

additional reflection probes

should be added and positioned appropriately

for the reflective objects.

It is worth noting that phyically-based rendering

works best in linear colour space.

Linear colour space will give

a more realistic and mathematically correct result.

For best results make sure that

the colour space is set to linear

in the project's

Player Settings window.

Linear colour space is the default setting.

Be aware that not all platforms

support linear colour space however,

and that gamma is currently the

required colour space for most mobile platforms,.

When looking at all these aspects

to lighting a scene in Unity

they can be summed up effectively

with the main contributory factors.

Ambient light.

Reflections.

And light sources.

Working with materials created

with the standard shader being

drawn using phyically-based rendering

with global illumination to calculate

the indirect light and create

more complex, more realistic scenes.