Lining the underside of the cover with water proof royal blue SMD LED strips would give enough light for cheato to thrive. Or a single Luxeon or Cree LED star on a small strip of aluminum, but water proofing that on the underside of the lid would take some creativity, on the other hand you could put the heatsink on the top of the lid and drill a small hole thru for the emitter and silicone a piece of acrylic over the bottom of the cover.
