Default value THREE.CullFaceFront, other valid value THREE.CullFaceBack.

These constants also go into renderer.setFaceCulling( cullFace, frontFace ) where they replace strings:

"back"  => THREE.CullFaceBack
"front" => THREE.CullFaceFront
"frontback"    => THREE.CullFaceFrontBack
""/0/undefined => THREE.CullFaceNone

See discussion in #2683