Incandescent bulbs

When I was a kid, living with my extremely tolerant parents, I had about 
20 aquariums in my bedroom.  The tanks were stackedagainst two walls and 
were three deep.  I used nothing but 40 and 60 watt bulbs throughout.  
The heat generated by the bulbs rose up through the shelves and heated 
the tanks above, giving me a heated substrate.  Several spp. bloomed in 
there, including some bog plants, i.e. water poppy.