Hi Roediger! Saw your post late but we just installed a 30 inch (76 cm) planted+ 24-7 on our 20 gallon long. We are running low tech and that light is reported to produce 75 PAR at the tank bottom ( 30 cm) so with substrate, a bit stronger. We placed a double layer of black window screening to the bottom of the light. I had read somewhere that a general calculation of a double layer of screen is about a 60% reduction. So roughly 45 PAR it is producing in our tank, same as yours. How is the light working for you? Have you had any algae issues? How have your plants and animals responded to it?