A few hours a day is probably enough. If it's LED you can probably adjust the color temperature too, so like a warmer light in the evening and a bluer light in the morning, maybe pure white around late morning/early afternoon. Or just get three different bulbs.

Might help for a few hours of high-focus time, then take a break with some dimmer light to reset. Doesn't need to be all day.

Doesn't need to be 30k lumens either. 5k-10k is already insanely bright and should be effective when combined with the right white-balance. Even 500-1000 lumens is plenty bright enough for most purposes. Higher kelvins (like 5k-8k) makes the light more bluish and that's what's most important for treating SAD. Some UV spectrum is helpful for that too as it helps with vitamin D synthesis

If color fidelity is important to your line of work, a bulb with 90-100 CRI is a great idea too.

My desk lamp has a 500 lumen, 5000 kelvin, 90+ CRI bulb and I can't imagine a situation where I would need it to be brighter. I have a similar bulb that's 1100 lumens but it feels like overkill.