Clarifications and fixes for light extensions

[lelievres]

This pull request addresses issue #20 on MPEG light extension.

[edrthomas]

Thanks @lelievres for work. The changes look good but I would suggest we hold on on this PR until we process the input https://git.mpeg.expert/MPEG/Systems/SceneDescription/MPEG-Contributions/-/issues/946.

This contribution proposes the modify again this aspect ...

[edrthomas]

@lelievres @ibouazizi I have updated the schema with the spec, please check.

[lelievres]

@lelievres @ibouazizi I have updated the schema with the spec, please check.

Thanks @edrthomas for the updates. It looks fine to me.
My proposal is to apply the change to the https://github.com/MPEGGroup/glTF (I can handle that) and to finalize the check through the corresponding pull request (MPEGGroup/glTF#3).

[lelievres]

@lelievres @ibouazizi I have updated the schema with the spec, please check.

Thanks @edrthomas for the updates. It looks fine to me. My proposal is to apply the change to the https://github.com/MPEGGroup/glTF (I can handle that) and to finalize the check through the corresponding pull request (MPEGGroup/glTF#3).

Done!