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Lights and environment

Light comes from three places: PT LIGHT components, surfaces whose material Emits, and the HDRI map around the scene. Mix them freely.

PT LIGHT

A PT LIGHT is an area light: a glowing surface that casts soft shadows. The larger it is, the softer the shadows. Place it with its Xform page like any object; it shines from both sides.

  • Type picks the shape: a 2 × 2 Rectangle, a Circle, a thin Ring, or a tiny Point that gives hard shadows. Wire any POP into the PT LIGHT to use that as the shape instead.
  • Color and Emit set its colour and brightness.
  • Color Texture puts an image on the light, which then shines in the image's colours, like a screen or a stained glass window. The shape needs texture coordinates (Texture Coordinates).
  • Normalize by Area keeps the light's total output the same when you resize it, so scaling a light makes its shadows softer without making the scene brighter. Turn it off to make Emit the brightness of the surface itself.
  • Render as Light Source off hides the light's surface from the camera; it still lights the scene and shows in reflections.

Emitting materials

Any geometry lights the scene when its PT MAT has Emit above 0, in the material's Color: a neon tube, a TV, a glowing sign. Emit can also come from an attribute or a texture, to make only parts of a surface glow (see Materials).

The HDRI map

HDRI Map on the Pathtracer takes an equirectangular (latitude-longitude) image, ideally a high dynamic range file such as an .exr or .hdr in a Movie File In TOP. It surrounds the scene and lights it from all directions, which gives natural reflections and soft light.

  • Dimmer sets its brightness, and Rotation turns it around the scene.
  • Render as Background shows it behind the scene. Turn it off to keep its light but show a black background.
  • Apply Dimmer to Background sets whether Dimmer also changes the visible background.
  • MIS HDRI Map: turn it on when the HDRI has a small, very bright source such as the sun. Light paths are then aimed at the bright parts, which removes most of the noise such a source causes.

Hiding lights from the camera

Render Light Sources on the Pathtracer hides every light and emitting surface from the camera at once, while they keep lighting the scene and showing in reflections. Useful for product shots with large softboxes.

Noise and fireflies

Small, bright lights make more noise than large ones, and very bright spots reflected in rough surfaces can leave single bright pixels, called fireflies. Remedies, from gentle to strong:

  1. Make the light larger, or use MIS HDRI Map for a bright HDRI.
  2. Raise Rays Per Pixel, or let the Average method run longer.
  3. Set Firefly Clamping. It limits how bright a single light path may be; lower values remove more fireflies but also dim small highlights.