Lights

The pyvista.Light class adds additional functionality and a pythonic API to the vtk.vtkLight class. pyvista.Plotter objects come with a default set of lights that work well in most cases, but in many situations a more hands-on access to lighting is necessary.

Brief Example

Create a red spotlight that shines on the origin, then create a scene without lighting and add our light to it manually.

import pyvista as pv
from pyvista import examples
light = pv.Light(position=(-1, 1, 1), color='red')
light.positional = True

import pyvista as pv
from pyvista import examples
plotter = pv.Plotter(lighting='none')
plotter.background_color = 'white'
mesh = examples.download_bunny()
mesh.rotate_x(90)
mesh.rotate_z(180)
plotter.add_mesh(mesh, specular=1.0, diffuse=0.7, smooth_shading=True)
plotter.add_light(light)
plotter.show()
../../_images/lights-1_00_00.png

For detailed examples please see Lighting.

Light API

pyvista.Light instances come in three types: headlights, camera lights, and scene lights. Headlights always shine along the camera’s axis, camera lights have a fixed position with respect to the camera, and scene lights are positioned with respect to the scene, such that moving around the camera doesn’t affect the lighting of the scene.

Lights have a position and a focal_point that define the axis of the light. The meaning of these depends on the type of the light. The color of the light can be set according to ambient, diffuse and specular components. The brightness can be set with the intensity property, and the writable on property specifies whether the light is switched on.

Lights can be either directional (meaning an infinitely distant point source) or positional. Positional lights have additional properties that describe the geometry and the spatial distribution of the light. The cone_angle and exponent properties define the shape of the light beam and the angular distribution of the light’s intensity within that beam. The fading of the light with distance can be customized with the attenuation_values property. Positional lights can also make use of an actor that represents the shape and color of the light using a wireframe, see show_actor().

Positional lights with a cone_angle of less than 90 degrees are known as spotlights. Spotlights are unidirectional and they make full use of beam shaping properties, namely exponent and attenuation. Non-spotlight positional lights, however, act like point sources located in the real-world position of the light, shining in all directions of space. They display attenuation with distance from the source, but their beam is isotropic in space. In contrast, directional lights act as infinitely distant point sources, so they are unidirectional but they do not attenuate.

Shadows

With directed lights, it is possible to create complex lighting scenarios. For example, you can position a light directly above an actor (in this case, a sphere), to create a shadow directly below it.

The following example uses a positional light to create an eclipse-like shadow below a sphere by controlling the cone angle and exponent values of the light.

import pyvista as pv

plotter = pv.Plotter(lighting=None, window_size=(800, 800))

# create a top down light
light = pv.Light(position=(0, 0, 3), show_actor=True, positional=True,
                 cone_angle=30, exponent=20, intensity=1.5)
plotter.add_light(light)

# add a sphere to the plotter
sphere = pv.Sphere(radius=0.3, center=(0, 0, 1))
plotter.add_mesh(sphere, ambient=0.2, diffuse=0.5, specular=0.8,
                 specular_power=30, smooth_shading=True,
                 color='dodgerblue')

# add the grid
grid = pv.Plane(i_size=4, j_size=4)
plotter.add_mesh(grid, ambient=0, diffuse=0.5, specular=0.8, color='white')

# setup and show the plotter
plotter.enable_shadows()
plotter.set_background('darkgrey')
plotter.show()
../../_images/lights-2_00_00.png

Note

VTK has known issues when rendering shadows on certain window sizes. Be prepared to experiment with the window_size parameter.

API reference

Light([position, focal_point, color, ...])

Light class.