A small ~7" worklight reflector from Lowes or HD with a CFL bulb in it works great and is cheaper than the floodlight bulbs in the long run. Actually puts out quite a bit more PAR too (using equivalent wattage floodlight and regular CFL bulbs in reflector to compare), the worklight reflector does a much better job than the floodlight's. I use 100W equivalent (27W actual) Home Depot's 'daylight' CFL bulbs to grow many kinds of macroalgae readily. The daylight is a little more blue than soft white or 6500K, looks better and does just as good if not a little better than the more yellow bulbs. Most macroalgaes are used to a little bluer of a spectrum than terrestrial plants anyway.