I was able to reach the "Powerful Light Energy" level (Moghancement Strength 51-100) with a full set of 8x Mannequins and an Adventuring Certificate (Reported to be Light +3), but not without the certificate.
This gives a calculated Light Elemental Strength of +6.
Ofcourse. Result of the "It's raining mannequins" quest will be the mannequin of your racegender, but an upcoming patch will allow you to buy the other mannequins, provided you have done the quest.
The mannequin parts are rare/contraband, so you can sell them in bazaar, but not AH or send them through d-box. The mannequin itself is rare/ex, so it can't be sold to people.