LED and wattage is also tricky to answer..
And with LEDs the times are over that brightness and wattage could somehow be related as it used to be with oldfashion bulbs and tubes.There are so many different types of leds in a range from 15 to 100 lumen per watt and some calculate lumen per led on the pcb.
Than in the old days it was simple with a tube light giving x amount of lumens at x watt it was pretty steady..Than common practice was if 2 tubes are used, simply add the lumen of both tubes together for a total. But nowadays a led tube is build with for example with 72 small led as single light source per metre that could produce 50 lumen per led. 50 lumen is about nothing only good for finding a keyhole in the dark, 50 x 72 = quite a bit stronger. But if the total is 3600 lumen is rather very doubtfull, more likely far from it. But that is still the formula used by vendors and the general publiic. Just to get an idea which is brighter and then stick a fictional number to it for convenience. And still with the general idea more watage is more light.. But it aint anymore with leds. Without any flux/par measuring equipment it is all the customer has to go with you never know if they sell you the truth.
But indeed
I do have a dimmer in case it’s too bright.
Than find something dimmable and take something rather over calculated and you can't go wrong if it prooves to be to much at full power.
For example read the Journal section find setups in comparable dimensions and plants they grow etc. Most journals have their equipment specified usualy also amount of lumens for the lights and or what kind of light is used from which you likely can look up its performance to compare. See the results they adchieve and use this information to get an idea what you might need for your own setup.
I used on a simmular dimension 40x25x25cm tank 2 x COB led lights - specified with 1350 lumen each and 30 watt total, installed it with a dimmer and it performed like a charm at 70% with easy t grow plants.
And or searching around i also find other/newer types of leds alledgedly performing the same at 20 watt..