Photoperiod and general light exposure

Houpt, Katherine A., Hollis N. Erb, and Genaro A. Coria-Avila. “The sleep of shelter dogs was not disrupted by overnight light rather than darkness in a crossover trial.” Animals 9.10 (2019): 794.

The population studied consisted of 10 dogs (four males and six females).
The timing of treatments was balanced so that half the dogs were filmed first in the light provided by a standing lamp with a 200-watt bulb (3000 lumen), or by florescent light (2000 lumens) which could not be extinguished in an adjacent hallway and the other half first in the dark (no light source in a windowless building).
no differences in total minutes slept, number of sleep bouts, or time active
extremely small sample size though

Piccione, Giuseppe, et al. “Influence of different artificial lighting regimes on intraocular pressure circadian profile in the dog (Canis familiaris).” Experimental animals 59.2 (2010): 215-223.

similar, no difference of photoperiod on intraocular pressure (a factor of circadian rhythm), but extremely small sample size (10 dogs)

European Food Safety Authority (EFSA), et al. “Scientific and technical assistance on welfare aspects related to housing and health of cats and dogs in commercial breeding establishments.” EFSA Journal 21.9 (2023): e08213.

Gotta love EFSA!! Amazing review articles for both my work (chicken welfare especially!) and for my doggies.
Defining the parameters for artificial light (i.e. the illuminance (lux), the spectrum and the light-time schedule) would be important for breeding cats’ and dogs’ welfare; however, more research is recommended to define these parameters quantitatively and qualitatively.
White artificial lighting, preferably broad or full spectrum
From the scoping literature search, there is available evidence that setting parameters for artificial light is important for breeding dog welfare.
Parameters for artificial light should be set, however more research is recommended to define light parameters quantitatively and qualitatively. The frequency of artificial light should never be lower than 80 hertz.
Artificial light at a lower frequency than 80 hertz produces flickering which can be disturbing to the animal.

Flicker

Inger, Richard, et al. “Potential biological and ecological effects of flickering artificial light.” PloS one 9.5 (2014): e98631.

Little considered is that many types of lamp do not produce a constant stream of light but a series of pulses. This flickering light has been shown to have detrimental effects in humans and other species. Whether a species is likely to be affected will largely be determined by its visual temporal resolution, measured as the critical fusion frequency. That is the frequency at which a series of light pulses are perceived as a constant stream. Here we use the largest collation to date of critical fusion frequencies, across a broad range of taxa, to demonstrate that a significant proportion of species can detect such flicker in widely used lamps.
A key measure of the temporal resolution of vision systems is the critical fusion frequency (CFF), the threshold at which an animal ceases to perceive a flickering light source as a series of flashes, but rather as a continuous stream of light. An obvious first step towards assessing the likely effects of the flickering of artificial lights on animals other than humans is to determine in which species the CFF is higher than the flicker rates of widely used electrical lamps, and hence those that will perceive the light source as flickering.
in table 3, dogs are reported to have a mean CFF (critical flicker frequency) of 75.0

https://www.sunlightinside.com/light-and-health/light-flicker/

Humans can see lights flicker up to 60-100 Hz (60-100 cycles per second) which is called the critical fusion frequency
The electricity which comes out of a regular wall socket alternates at 50 or 60 Hz (AC = alternating current) which means the power feeding most lights is cycling on/off 100 or 120 times a second. As a result, many light sources flicker at 100 or 120 Hz, since they have power twice in every cycle. Almost all artificial light sources are associated with flicker, including TV screens and computer monitors.

So flicker is probably fine, seems similar in dogs and humans.