Barebow, I had the problem you mentioned intially. Urinated me off to find out I had to buy another $30-40 part to make it work inside, so...

I suspended 2 75 watt light bulbs screwed into temporary light sockets (like contractors use to provide temporary lighting), one about 1' above each diffuser, stuck the ends of the socket leads into an extension cord, plugged it in, worked like a charm, for a grand total of $0