Difference between revisions of "Lighting"

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===IES data===
===IES data===
IES files contain information about the light distribution of a lighting fixture. These files are typically provided by lighting fixture manufacturers.
With the help of IES files you can get the light distribution pattern of a real light fixture. This will keep render times down as you don't need a reflector or glass material to replicate the pattern. More information about IES files and how to create your own can be found here: [[Lighting_With_IES_Files]]


[[Image:IES_examples.jpg|frame|left|a number of IES data files]]
IES_examples image


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The main use of IES is measuring real world lamp models, many manufacturers sites offer their IES library for free. Generic IES can also be made with applications like "ies generator". Since IES profiles can be applied to mesh lights and area lights, they can be used to control the light spread angle, much like a spotlight cone. Area lights with the IES profile of a spot will illuminate like a spot but will have a physical size. This will make them easier to balance in intensity with other physical lights.
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However, to have the physical intensity of a specific IES scaled correctly, the IES must be used with point lights (mesh and planes will still make the correct 'shape', but the intensity will be altered by their power, efficiency and size)
===Color and Spectrum===
LuxRender calculates light colors using actual spectral data (is that true for luxcore too? ). When using an RGB color as input, LuxRender will generate a physically plausible spectrum based on the desired color. The implementation is based on a [http://www.cs.utah.edu/~bes/papers/color/ paper by Brian Smits].


However, you can also define a spectrum for the light source in a variety of ways, using spectrum textures. For more information, see [[LuxCoreRender Textures Spectrum]]


[[Image:Lightcones2.JPG]]
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On the left: a single quad mesh light using a "narrow cone" IES : resulting light (from a cylinder) makes "petals" as if the sides were separate
spotlights, on the right: a "wide cone" IES makes almost a uniform ring shape.
 
And these are the corresponding IES diagrams:
 
[[Image:Iescones.jpg]]
 
These simple shapes make light "cones", complex shape make various effects (wallwashers , multiple beams..) The diagram: what you see in IES viewers or iesgen4 reads like this: in the center there is the light source. Around it, infinite rays going in every direction (generally represented in 2d, the 3d shape is obtained by visualizing the spinning of the 2D graph around a line in the plane)
 
Each ray represents the light going out of the lamp in a particular direction (towards the floor, walls, ceiling). The length of the ray is the intensity of light in that direction. The shape you see is made by the tips of all rays.
 
A circle means intensity is the same in all directions, a thin and tall ellipse means a narrow light cone going downwards (or up). Intensity scale (units): the intensity at all directions affects the overall brightness of the lamp; a light sending rays of maximum intensity (1.0) on a small angle (like a ellipse diagram) will be dimmer than a light with intensity 1.0 in all directions (a circle diagram).
Most ies files have a 2D diagram meaning that the light distribution is symmetric all around the lamp axis. Some files have 3d diagram, made by two sections (the 2nd also made on the lamp axis but rotated 90°) they're visible in iesviewer in red and pink. For placing these asymmetric lights in your scene, rotation on vertical axis counts.
 
 
There is unfortunately no standard for intensity. It can mean that of a specific bulb (i.e. 40W), a generic power (i.e. 100W and you have to use "gain" in the exporter as multiplier to adjust it). Or in generic IES files can have intensity 1.0 and "gain" is used to specify their power (IES suppliers specify what rule they used on their site or documentation).
 
Diagram types: that above is a "polar" visualization of the IES with the rays drawn around the center (used in iesviewer and iesgen4) it's the easier to read as it resembles the actual shape of the light. The other possible visualization is a Cartesian (XY) diagram, as used by iesgen3, shows ray intensity on Y and the direction on the X axis (on the left it's intensity in the center of the cone (the light axis), on the right the intensity perpendicular to that ) this is less intuitive but makes easier to draw simpler curves for generic IES.
 
[[Image:Iesgen3penumbra.jpg]]
 
Top: the same "narrow cone" ies as before seen in iesgen 3 (xy diagram)
Bottom: an IES with similar cone angle but "sharper" (smaller penumbra angle)
 
LuxRender can also use IES files with both vertical and horizontal angle data.
 
[[File:3D_IES_13Oct2013.jpg|400px|thumb|left|IES light with both vertical and horizontal data.]]
 
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IES files can also be generated by hand, as the 3D IES file used in the image above was generated by hand. A good place to start is to open an existing IES file and start modifying it. You can find standard IES file format specifications by doing a quick internet search.
 
Useful links (freeware, for windows , working in wine)
[http://www.tom-schuelke.com/ies-gen3.exe]
[http://rip3d.net/Downloadmodels/iesgen_4.rar]
[http://www.rip3d.net/web/en.html#/free/downloads]
[http://www.cgarena.com/freestuff/tutorials/max/ieslights/IESviewerSetup.rar]
[http://www.lithonia.com/Photometrics.aspx]
 
Some links to IES data files can be find on our [http://www.luxrender.net/wiki/External_resources#IES_lighting_files external resources] page.
 
 
 
===Colour and Spectrum===
LuxRender calculates light colors using actual spectral data. When using an RGB colour as input, LuxRender will generate a physically plausible spectrum based on the desired colour. The implementation is based on a [http://www.cs.utah.edu/~bes/papers/color/ paper by Brian Smits].
 
However, you can also define a spectrum for the light source in a variety of ways, using spectrum textures. For more information, see [[LuxRender Textures Spectrum]]

Revision as of 16:19, 12 December 2017

Area Lights and Mesh Lights

The most common way of lighting in LuxCoreRender is by using area lights. With this light you are able to simulate a wide range of lighting. It supports common settings such as power and color but also spread angle, opacity and laser.

Another common way is by using mesh lights. This type of light supports the same features as area lights, except laser, but also features textured lighting. As mesh lights are objects, you can assign an entire object to emit light, such as the tungsten filament in a light bulb or halogen bulb. In general, it's advised to use mesh lights with as few faces as possible to keep render times down.

Objects only emit light in the direction that the normals of the object's faces are pointing.


Environment Lighting

Environment lighting encloses the scene entirely, lighting it from all angles. It is normally used for environment mapping, although it can also be used to add a solid color environment. LuxCoreRender accepts both latlong and angular (light probe) environment maps.

Environment lighting is usually done with HDR(high dynamic range) images but it is possible to use low dynamic range images (like JPG or PNG) as well, but in this case you may want to add some additional lighting to your scene to avoid getting a poorly contrast render. This is not necessary with HDR environment maps, which can be used as the only source of light to create a realistic lighting.

You can find a lot of free quality HDR maps on the web by looking for "hdr maps"/"hdri maps" or "light probes".

For more information on environment mapping, see the Environment map page


File:Lightingtypes.jpg
lighting using HDRI maps (left two images), a physical sky and an infinite environment (right). HDRI maps by Doug Hammond



Sun and Sky

The sun and sky light creates a lighting setup that simulates the light of the sun and atmosphere, based on the direction of a sun light in the scene and a parameter named turbidity which defines the clearness of the sky. Both the sun angle and the sky clearness influence the color of the light.

File:Sunsky.png
various sun angles result in different sky and light colors


File:Turbiditysettings.jpg
turbidity settings of 2, 4, 8 and 16, influencing both sky clarity and color


The intensity of the light can be set with the gain parameter. This is useful in scenes where the sun and sky light is combined with area/mesh lights. Note that the sun lamp is very bright(as it is in real life) so you may have to turn it way down if combined with other lights. The other lights may look like they are not even emitting, but they are actually overpowered by the sun.
If you want softer shadows try adjusting the relative sun size parameter.

It is possible to use this light with only the sky, or only the sun.


Point Lights

Point lights are infinitely small light sources that emit light in all directions. Apart from their location, the only available setting is color, which can also be used to regulate intensity.

In most cases, it's recommended to use only mesh/area lights and environmental lighting for your scene, rather than point or spot lights. This is because the point and spot lights have no real world equivalent as the light source is an infinitely small point. As a result, they tend to produce unnaturally hard lighting and sharp shadows.


Spot Lights

Spot lights are infinitely small lights that emit light in a cone shape. Apart from color and location, the width of the cone can be set (as the number of degrees of the center line it will extend), and there is a setting to feather the intensity towards the edge.

As with the point lights, it's recommended to use only mesh/area lights and environmental lighting. This is because the point and spot lights have no real world equivalent as the light source is an infinitely small point.


Projector Both point lights and spot lights can distribute their light and color according to an image. With spot lights, this results in an effect like something being projected from a diapositive projector or beamer. With point lights, the image map is spherically mapped. <-- check if this works in luxcore

File:Projector.jpg
a room lit by a single projector


File:Lights-01.jpg
An example of point (left) spot (center) and area (right) light types



IES data

With the help of IES files you can get the light distribution pattern of a real light fixture. This will keep render times down as you don't need a reflector or glass material to replicate the pattern. More information about IES files and how to create your own can be found here: Lighting_With_IES_Files

IES_examples image