Noisy Renders in Blender Cycles
Grain and white dots in Cycles renders
Also known as: Blender Cycles noise · Blender fireflies · Blender render grainy · Blender denoise · Blender white dots render
Quick answer
Grain in a Cycles render means too few samples for the lighting in the scene. Turn on Denoise in Render Properties, raise the sample count, and keep Adaptive Sampling on so Cycles spends time where noise remains. For bright white dots, called fireflies, lower Clamp Indirect in Light Paths, and avoid tiny, very bright light sources and strongly glossy surfaces lit indirectly.
How to fix it
Better lighting reduces noise more than more samples do: use larger lights, an HDRI and fewer indirect-only light paths. Denoise can smear detail, so compare at full size, and render at a lower sample count with denoising for drafts. Use the GPU for Cycles if you have one. For quick previews, Eevee needs far less time but gives different light and reflections.
Tools that use Noisy Renders in Blender Cycles
See also
Eevee vs Cycles
Blender's real-time and path-traced renderers
HDRI
High Dynamic Range Image lighting
Global Illumination
Light bouncing between surfaces
Principled BSDF
Blender's all-purpose PBR shader
Ambient Occlusion
Soft contact shadows
Denoising
Cleaning noise from low-sample renders
Path Tracing
Physically accurate light with random sampling