Hello; I have converted old light hoods over the years. Some were set up for the old incandescent bulbs and were simple to replace with screw in LED bulbs with a standard base.
I had two hoods that used 18 inch fluroscent tubes. I converted them to LED bulbs with standard bases. I got some standard sockets to replace the fluorescent guts and have made them work.
These screw in LED bulbs are working fine to grow my live plants. I prefer the "daylight" types closer to the 6500 K range.
On my 55 gallon tank I have been using a 48 inch LED shop light. It was on the discount rack at a local Wal-mart a while back for around $25. It happened to fit nicely on the existing tank cover. I know the chances of finding these on sale may not be so good, but LED lights are coming down in price bit by bit.
good luck