Unfortunately, moving plants further away is not an option due to space considerations. These will be seedlings growing on a shelf, and for maintenance purposes I prefer the top shelf to be lower than eye level. Four tiers maximizes the space I have. I mean I could buy less plants, but...
This is a case where there are trade offs in every decision. I looked at the dimmable LED lights and it seems that they're either too expensive, or that dimming degrades the spectral signature or something. In any case, no one sells grow lights that dim. Most of the aquarium lighting or dimmable grow lights that I saw use a proprietary format with a timer for e.g. 12 hours built into the dimmer, and lacks support for external timers, making them a non-starter.
On the other hand, I could just stick with my current lights and if it gets too bright and plants get too close, I'll put a 50% to 70% shade cloth in between. The problem with this is that it wouldn't be very power efficient. I'd be spending more electricity than I need then blocking off some of the light. It would generate more heat, which would need to be dealt with using more fans. I've bought a bunch of 12V computer fans since it seems this is the only option without spending some hundreds of dollars per light (per tier).
Edit: I measured again and it turns out the light level wasn't as high as when I first measured. I'm not sure what went wrong. But it seems it's not going to be a problem unless it gets within 2-3 inches or so. And since I'm only growing seedlings here that will be in this setup for a year or two max, until they're strong enough to be potted up and put outside... or something else -- so the plan goes... I'm hoping this won't be a huge problem.