Tank lighting can and does affect cichlid behavior. I have posted before about how some fish become killers at night whereas sometimes everything is calm and peaceful. See Lights on or lights off?, Lights off equals calm, When the lights are off, it’s not always tranquil. My show tanks are all individually lighted. My larger tanks, which are community tanks, also contain considerable cover (e.g., caves, rock work). The lights on those tanks are only on for a couple of hours each day. However, those same tanks are also exposed to ambient lighting (e.g., window light or room lights) about 14 hours a day, leaving my fish in complete darkness for the remainder.
Behaviorally, my fish (both Tangs and mbuna) are different during periods of no light, exclusive ambient light, and tank light. In no light, they largely “sleep” or what we call sleep, which is an anthropomorphization. In only ambient light, most of my fish are very calm and less energized, but out in the open (except my mbuna who are more out and about). Under tank light, many of my fish hide or otherwise at least partially conceal themselves. Some even become a bit erratic. This isn’t all that abnormal, especially in tanks with lots of cover.
So what’s the point? Light does have an impact on your fish’s behavior, often in conjunction with the amount of cover in the tank. If you have some generally shy fish, try observing them when the tank light is off and under ambient light alone. Even if you have very little cover, I would bet your fish are more active when the tank light is on. Why? A couple of reasons. First, light isn’t always a fish’s best friend. Light exposes fish to predators from both above and below, depending on the light. The innate sense of this exposure tells fish to be cautious (even in tank bred fish), which is why they might be swimming very actively. Laying idle in the open makes them a “sitting duck” in the wild, especially when they stand out because of the light. Second, you probably feed your fish when your tank lights are on. Thus, when the light comes on, your fish anticipate getting fed, or when they see you approach they anticipate getting fed. Such anticipation promotes active swimming as they begin jockeying for feeding position.
It’s a bit hard to tell in the two photos above, but in the top photo with the tank light on you can see some of the fish (shellies) higher up in the water column. They see me in front of the tank about 4 feet away and anticipate getting fed. The bottom photo is the same tank with the tank light off and only overhead, ambient light on. The fish have mostly moved back down toward the substrate and their shells, even though they can still see me. NOTE: The two photos weren’t taken at the same time. They were taken about 30 minutes apart (the photo with tank light on was taken first).
As I alluded to earlier, in my mbuna tank the fish are out in the open more under ambient light. That tank has lots of cover. When that tank light comes on, the fish dart toward the cover. This runs counter to some of what I said above, which I think is for two reasons. One, the amount of cover I have and two, I have few fish. Many hobbyists provide little cover in their mbuna tanks, and many of those tanks will contain a dozen or more fish. It’s a common practice in mbuna community tanks to overstock in order to mitigate aggression. I think that is the rule rather than the exception for most mbuna keepers. Thus I am certain that I am in the minority of mbuna keepers.
Observe this in your own tank(s) sometime. Watch your fish under different lighting conditions and see if they, overall, behave differently under different conditions. I bet you’ll be surprised if you’ve never noticed before.