Who's arguing

I'm pretty sure the algae is only going to grow as long as their are nutrients to consume. So whether or not you have your sump lights on for 3 hours, 12 hours, or 24 hours, as long as they are soaking up all your nitrates and phosphates I dont see how it really matters. Unless the pH is more stable one way from another

 

Regarding 24/7 light on macroalgae... there are a few things to consider.

1) Although most text books split the photosynthetic reactions into the "light reactions" and "dark reactions", this is really just poor terminology and is misleading. The "dark reactions" in macro algae happen all the time, including during the day. A dark period is not always required.

2) The main idea behind a dark period is that it prevents the photosystems/ electron transport carriers from becoming over reduced, or in other words not saturated with electrons. If too many photons hit the light harvesting complex too quickly, then photosynthesis will become saturated, and the extra energy from the extra photons will be shed in other ways, such as heat or fluorescence. In extreme cases, this can damage or kill the cell.

3) Light also plays non-photosynthetic roles. For example, in the reproductive cycle for some species.

So, in my opinion, as long as you are not using highly intense lighting there are no issues with lighting most algaes 24/7. If you want a number, I'd estimate 50 umol/m2/s is safe for most species. The number likely varies by orders of magnitude however, some species will tolerate much more light.

On a side note, the literature for micro algae overwhelmingly supports 24/7 lighting.

 

I have 4 light fixtures on 4 timers

Noon - 10:30 = Blue LED Strip
1:00 - 9:30 = Actinics
2:00 - 8:00 = 1x 10k / 1x Blue Plus
3:00 - 7:00 = 1x 10k / 1 x Blue Plus

 

All on your macro algae?

 

no, main 'display' tank.

The OP didn't say anything about refugiums or macro algae, just asked about lighting.

I just gave my response to OP.

I don't run a refugium.