The short answer for corydoras lighting
Corydoras are bottom fish from shaded streams and leaf-strewn pools, and their lighting should feel like that home: moderate rather than brilliant, steady rather than erratic, and broken by real shade at floor level. A timer giving roughly eight hours of light a day suits most community and species tanks, and the brightness only needs to satisfy the plants. What transforms a cory tank is cover over the substrate: plants arching above the sand, driftwood overhangs, and leaf litter in corners, so the group can choose between lit foraging lanes and dim resting shade without leaving the bottom layer where they live.
Why bright, bare tanks shut corys down
Keepers often meet corydoras as a row of fish parked under the filter, apparently doing nothing, in a tank that is brightly lit with nowhere to hide. That stillness is a lighting verdict. In the open glare over pale, uncovered sand, a small bottom fish feels exposed to every passing shadow, so the group freezes together in the one dim spot and waits for dusk. Give the same fish dappled light and floor-level shade and the behaviour flips: they nose through the sand in twos and threes, rest in loose piles under leaves, and make their famous dashes to the surface throughout the day. Light level also interacts with substrate; a gentle light over dark sand reads far dimmer to the fish than the same lamp over bright white gravel, so judge the combination, not the lamp alone.
Setting a schedule the group can trust
Corydoras thrive on rhythm. Fix the timer, keep the same hours daily, and let room light soften the transition before the main light comes on where possible, because a tank that snaps from black to full brightness startles bottom fish into the glass. An evening ramp-down or a short period of dim light before darkness lets the group shift into its more active night foraging naturally, and corys are often at their busiest in the hour after lights-out. Avoid the keeper's habit of switching the light back on late at night to show guests the fish; repeated interruptions fragment the rest the group takes in its shaded piles. If algae pressures you to cut hours, cut them gradually and watch that plants shading the sand survive the change, since losing the cover hurts the fish more than losing an hour helps the glass.
Shade design for a working bottom layer
Build the shade where the corys actually are. Broad-leaved plants rooted at the back cast shadow forward as they grow, wood pieces laid low make instant caves of dimness along the sand, and a corner of leaf litter gives the group a dark, soft resting bed that also grows the microscopic foods they sift for. Keep some open sand in moderate light too, because watching the group forage there is how you spot a thin fish, a damaged barbel, or leftovers building up. If your group still hides all day after the lighting is softened and the shade is built, look next at group size and companions, since corys kept in twos or under boisterous tank mates stay shy under any lamp. When the whole household tends the tank, KinsLe's Family Sharing keeps the light timer, shade plan, and group notes in one shared profile everyone can follow.