Hello,
You can check 'PoE configurable options' in the link below:
http://www.juniper.net/documentation/en_US/junos14.1/topics/task/configuration/poe-cli.html
And also the link below to understand LLDP Power negotiation.
http://www.juniper.net/documentation/en_US/junos14.1/topics/task/configuration/802-1x-lldp-cli.html
Regards,
Rushi