### Section 7.5.6.3Cylindrical Lights

Cylindrical light sources work pretty much like spotlights except that the light rays are constraint by a cylinder and not a cone. The syntax is:

You should keep in mind that the cylindrical light source is still a point light source. The rays are emitted from one point and are only constraint by a cylinder. The light rays are not parallel.

### Section 7.5.6.4Area Lights

Area light sources occupy a finite, one- or two-dimensional area of space. They can cast soft shadows because they can partially block light.

The area lights used in POV-Ray are rectangular in shape, sort of like a flat panel light. Rather than performing the complex calculations that would be required to model a true area light, it is approximated as an array of point light sources spread out over the area occupied by the light. The intensity of each individual point light in the array is dimmed so that the total amount of light emitted by the light is equal to the light color specified in the declaration. The syntax is:

light_source { <LOCATION> color <COLOUR> area_light <AXIS1>, <AXIS2>, SIZE1, SIZE2 adaptive ADAPTIVE jitter JITTER [ spotlight ] [ point_at <POINT_AT> ] [ radius RADIUS ] [ falloff FALLOFF ] [ tightness TIGHTNESS ] [ looks_like { OBJECT } ] [ fade_distance FADE_DISTANCE ] [ fade_power FADE_POWER ] [ atmosphere BOOL ] [ atmospheric_attenuation BOOL ] }

The light's location and color are specified in the same way as a for a regular light source.

Note that it is possible to specify spotlight parameters along with the area light parameters to create area spotlights. Using area spotlights is a good way to speed up scenes that use area lights since you can confine the lengthy soft shadow calculations to only the parts of your scene that need them.

An interesting effect can be created using a linear light source. Rather than having a rectangular shape, a linear light stretches along a line sort of like a thin fluorescent tube. To create a linear light just create an area light with one of the array dimensions set to 1.

When performing adaptive sampling POV-Ray starts by shooting a test ray at each of the four corners of the area light. If the amount of light received from all four corners is approximately the same then the area light is assumed to be either fully in view or fully blocked. The light intensity is then calculated as the average intensity of the light received from the four corners. However, if the light intensity from the four corners differs significantly then the area light is partially blocked. The area light is split into four quarters and each section is sampled as described above. This allows POV-Ray to rapidly approximate how much of the area light is in view without having to shoot a test ray at every light in the array. Visually the sampling goes like shown below.

The number of rays never exceeds the values you specify for rows and columns of points. For example area_light x,y,4,4 specifies a 4 by 4 array of lights. If you specify adaptive 3 it would mean that you should start with a 9 by 9 array. In this case no adaptive sampling is done. The 4 by 4 array is used.

Using the shadowless keyword you can stop a light source from casting shadows.

### Section 7.5.6.6Looks_like

Normally the light source itself has no visible shape. The light simply radiates from an invisible point or area. You may give a light source any shape by adding a looks_like { OBJECT } statement.

union { light_source { <100, 200, -300> color White } object { My_Lamp_Shape } }

Presumably parts of the lamp shade are translucent to let some light out.

By default POV-Ray does not diminish light from any light source as it travels through space. In order to get a more realistic effect fade_distance and fade_power can be used to model the distance based falloff in light intensity.

```                                 2
attenuation = --------------------------------------