public float shadowNormalBias { get; set; }

Shadow caster surfaces are pushed inwards along their normals by this amount, to help prevent self-shadowing ("shadow acne") artifacts. Units of normal-based bias are expressed in terms of shadowmap texel size; typically values between 0.3-0.7 work well.

Larger values prevent shadow acne better, at expense of making shadow shape smaller than the object actually is.

Currently normal-based bias is only implemented for directional lights; it has no effect for other light types.

Additional Resources: Light.shadows, Light.shadowBias properties.