これはシーン内の特定のオブジェクトを選択的に光らせることに使用されます。
A GameObject will only be illuminated by a light if that light's cullingMask/
includes the layer chosen for the GameObject (ie, the mask bit for the layer must be set to 1
for the object to receive any light).
See Layers for more information about layer masking.
See Also: Light component.