that's a fact that many have tested before me. the black lights are doing nothing for the anemone. keeping something alive and having it thrive are two different things. go to any LFS. you'll see anemones in 20 gallon tanks daisy chained together with only a single tube over them. they are certainly alive, but definitely not thriving.
i believe your trying to attempt to recreate a reef in your home. this would require ample lighting so that things stay healthy and brightly colored. We don't even know the lifespan of an anemone. we do know that it's more than 2 years. with supplemental feedings, i suppose it's possible, but why would you want to push the envelope and half-*** it?
the popular LED fixtures of today are using 3 watt (or higher)LEDs to stand up to the halide and T5 options. why would they do this if it was unnecessary?