I think it is ok to install some cool white (closer to daylight) light with a high CRI of 90-100Ra. This is useful for judging abilities of the plants well being.
If we do this we should have weather thight armature IP 44 (spatwater dicht) should be ok? I don't think the armatures we currently posses have this grade.
I found a light close to the 6500K you suggested... http://www.lampdirect.nl/philips-tl5-ho-90-de-luxe-54w-965-115cm-master/
It has a 6800K temperature, a Ra of 90-100 and 4300 lumen
I'm not totally sure if we should start using TL as a main source of growing light for our plans. What I do believe is that it will not harm to have some different wavelengths for our plans and probably even would be a good thing.