This is the simplest light source available, in some ways it is like sun, as it is omni-directional (i.e. shoots light in all directions from the point of its origin) and is spherical in nature. Since it shoots light rays in every direction, that means the ray going away from the scene will not make any visible changes in the scene, the light rays will be lost and thus are waste of computation. Although Ray tracers use a variety of hacks by cutting off the unwanted computations, it is a bit slower than other directional light sources if bigger parts of the light shot come inside the scene view.

The general use of Lamp is for indoor lighting, like rooms and halls, but it is not limited to this use, it is also more commonly used as filler light or helper light in the scene.

Values: When a single lamp is used for the scene in Yafray (through-out the tutorial when I say Yafray I mean Blender-Yafray), it will generally not provide sufficient lighting to light up the scene unless it is kept at a higher value. For the sample scene, the value of Lamp was set at 10 (maximum) but still there seems to be the need for additional lighting (but we are sticking to it for the sake of understanding). See Figure 28.9, “Rendered with Lamp at default settings.”.

Figure 28.9. Rendered with Lamp at default settings.

The Lamp will cast sharper shadows at default (zero) radius. The radius setting in Lamp is used to increase the area size for shooting the light. If the size of Lamp is bigger than the objects, then the light shot from some parts of the lamp could directly reach to the parts of the scene where the other part of the lamp casts a shadow. This intersection results in the shadow being diluted for that part, thus getting blurred (also called partial shadows). You can observe this phenomenon in real world (sun light).

LINK: for more info on shadow dilution or Partial shadows go to Ditto head's Light tutorial.

Figure 28.10. The noise comes when sampling values is low.

The scene above (Figure 28.10, “The noise comes when sampling values is low.”) was rendered at radius 2 with a sampling value at 1, as can be seen the scene has grainy partial shadows. The use of samples button is only to reduce the grain in shadows, the sampling buttons control the number of samples used in shadow calculations, increasing the sampling results in smoother shadows. The sampling button is only available in Lamp and Area Light and functions the same for both.

Figure 28.11. The increase in sampling to 5 remove the noise.

The Area Light is a directional source. The shape of Area Light can be varied from square to rectangular from the drop down list in the Lamp tab. Below the shape selection there is also an option to increase the size of the Area Light.

Figure 28.12. The basic render from Area Light at default setting and value of 4.

Values: For Area Lamp you will need lower light intensity values for rendering a scene with Yafray. The sample scene is lit by light value at 4, it is brighter than the one rendered by Lamp at value 10. This is because it is shooting all the light towards a direction from a plane while the Lamp shoots the light in every direction distributing energy where it may not be required.

Figure 28.13. Although the scene looks similar to Figure 28.11, “The increase in sampling to 5 remove the noise.” but is brighter and have better shadows.

The Spot is also a directional light source and as the name suggests it provides a circular spot of light or more appropriately a cone of light. The size of cone can be controlled by the SpotSi or angle of spotlight beam. The higher the angle the more nearer it behaves like an area light, but with one major difference. It cannot cast partial shadows. Spot light has a parameter to control the SpotBi or Spot's edge smoothness only. It can be seen only if the Spot light is inside the scene view, otherwise you will not notice any difference in Spot or other lights.

Figure 28.14. The Spot lamp render with default settings.

Figure 28.15. Spot lamp with spherical light attenuation.

Notice the increased brightness at the portion nearer to the lamp in the Figure 28.15, “Spot lamp with spherical light attenuation.” while using the Spherical light attenuation (Quad is not supported in Yafray). Increase in the distance value the spherical attenuation also increases in radius, for example the Figure 28.15, “Spot lamp with spherical light attenuation.” has a default distance value of 20 while Figure 28.16, “Spot lamp with Spherical attenuation enabled.” has the distance value at 30. The effect looks like that of typical household lamps where the attenuation is sharper.

Figure 28.16. Spot lamp with Spherical attenuation enabled.

This is also a directional light source. It tries to emulate sunlight by shooting light of the same intensity everywhere in the scene without attenuation (Figure 28.17, “The Sun light at value 2. No wonder why this lamp is called Sun.”). This results in the environment being lit up with constant ambience. Its value must be kept lower. The sample scene uses a light intensity value of .100. It is obviously good for out door lights, especially for a sun.

In outdoor scenes, if you do not want sharper shadows you can disable shadow casting for Sun, and use other lamps for shadow generation. But make sure they have sufficient light intensity to cast a shadow.

Figure 28.17. The Sun light at value 2. No wonder why this lamp is called Sun.

Hemi - Yafray does not support Blender's implementation of Hemi light internally; right now it just uses Yafray's implementation of Sun light instead.

Photon - Last of all, the Photon light source or photons lamp button is not to be confused with any light source. It does not cast any shadow or light, it is only used in Caustics* calculations and requires being placed or directed where you need the caustic calculation. Photon lamp shoots photons in an area, the photons are used by Yafray as the specialized ray elements only to calculate the caustics on passing through the objects like glass or mirrors, which have the property of bending light when passed through them, known as total internal reflection. Basically the placement of Photon lamp is to allow the user to optimize the rendering. Caustics is one of the most computation intensive jobs in Ray tracing.