I use 41w leds with 60° lens for 15gallon tank dimmed to 5% it's low light, i've been a high light user for few years, i was blind, i thought plant really needed high light, everytime i failed because lots of light increase everything needs, co2, nutrients, there is such a small margin of error with high light that it drived me crazy. I honestly can't handle it, too much work, too much stress. Must be easier in a big tank.
In one tank i have walichii and tuberculatum with co2, co2 is so hard to manage in high light tank, i needed so much co2 that i couldn't add any fish in it, wouldve killed them. With such lot of light (50% of the 41w led, 180 * 5630 led) there is no way i have the skill to manage that lol
So i went from 50% to 5%, at the beggining it looked weird, colors were washed out even more if your plant is not covering the substrate, but with time it look amazing..
For the first time i have success to grow walichii in perfect shape without stress, tuberculatum is growing nicely too. For the best color high light is amazing, but i once read ceg answer on the topic which said that growing plant for colors is a bad plan, growing them healthy is the goal and i think it's the truth, once you have nicely plant growth, it's all that matter, colors can come later.
CO2 growth plant not light, for the first time i agree with that, maybe i'm finally out of the matrix
12l means the margin of error is even smaller, if you want challenge go with 10w led but it's really high light, i'm too old for that lol