Your purple light is probably around 10000k and is high in blue and red (purple) light which is what plants need. Tall plants will grow to the surface and get light. It should grow any of the Echinodorus species that are taller such as amazonicus, bleheri, ozelot, barthtii, red special, red rubin, martii, uraguayensis etc. Also Hygrophilla stricta, polysperma, polysperma "rosanervig", salicifolia; Sagittaria, vallisneria, Ludwigia repens. As advised previously I would stay away from floating plants as they will block the light and be the only thing that grows well. The larger plants like Cryptocoryne and Echinodorus sp. will need feeding through the roots.