Why the same room can feel different at different hours
Core body temperature is not flat across the day. It follows a circadian rhythm, a roughly 24-hour internal cycle, and that rhythm is part of how the body manages heat [1]. The lowest point of core temperature, called the nadir, tends to fall during sleep time [2]. Because thermal comfort is tied to these internal processes, the hour on the clock can change how warm or cool a person reports feeling even when the surroundings have not changed [1].
This matters for how we read comfort complaints. A person who feels chilly in the evening and comfortable in the same spot the next morning may not be imagining it; their internal thermal state has moved. The review literature frames time of day as a real variable in thermal comfort studies rather than noise to be averaged away [1].
What light adds on top of the clock
Light is a separate input. A review of studies linking lighting to thermophysiology and thermal comfort set out to organize evidence on how light exposure affects body temperature regulation and how comfortable people feel [3]. That work treats light as something that can influence thermal responses, not merely as a visual condition.
The two factors can therefore stack. Time of day sets the background rhythm of core temperature [1][2], while light exposure may push thermal responses in one direction or another [3]. For a reader trying to explain a personal experience, the practical implication is that brightness and hour are both worth noticing, and that a bright room at the wrong time of day is not the same situation as a dim room at that same hour.
Does the feeling match what the body is actually doing?
Not necessarily, and the gap is the interesting part. Thermal sensation is a perception, while core temperature and skin temperature are measurements of the body's physical state. The time-of-day work connects the perception to physiological responses including skin temperature changes [2], and the circadian review ties comfort to core temperature rhythms [1]. That is a link between feeling and physiology, but it is not a guarantee that the two move in lockstep.
Outdoor evidence adds a further wrinkle. Among elderly people across different climate zones in China, visual factors including light intensity and solar color temperature were examined as influences on thermal comfort perception [5]. This is a perception study in a specific group and setting, so it speaks to how light shapes reported comfort rather than to measured internal temperature regulation. The distinction is worth holding onto: a change in what someone says about warmth is not the same as a change in what their body is doing to manage heat.
Where the picture is still forming
The direct evidence on light and time of day acting together is thinner than the question deserves. The time-of-day review explicitly does not address light level [1], and the dynamic thermal perception study did not examine light level either, using a long-wavelength light condition mainly to limit interference [2]. The light-focused review addresses light's role but is a structuring of existing studies rather than a single decisive experiment [3].
One older study sits at the edge of the question. In wheelchair shooters, heat affected performance, and the work discussed thermal sensation, skin cooling, and core temperature in relation to light intensity, with signals described as being read by receptors as variations in light intensity [4]. That is a narrow athletic context from decades ago, so it hints at a light–sensation–core temperature connection without settling how it works for people in everyday settings. Taken together, the evidence supports the idea that both light and time of day matter for thermal comfort, while the precise way they combine, and how closely the felt temperature follows the regulated one, remains an open question.
Sources used in this answer
Human thermal perception and time of day: A review
Reviews evidence that circadian rhythms in core body temperature and thermoregulation influence thermal comfort, and that time of day should be treated as a variable in comfort studies; it does not address light level.
Effect of time-of-day on human dynamic thermal perception
Examines how time of day affects dynamic thermal perception and physiological responses such as skin temperature, noting that the core body temperature nadir occurs during sleep time; light level was not examined.
The influence of light on thermal responses
Reviews studies relating light exposure to thermophysiology and thermal comfort, including effects of light at different times of day on core body temperature regulation.
The effects of heat on performance in wheelchair shooters
In wheelchair shooters, heat affected performance, and thermal sensation, skin cooling, and core temperature were discussed in relation to light intensity as a signal.
Assessment on the impact factors of outdoor thermal comfort among the elderly across diverse climate zones in China
Among elderly people across climate zones in China, visual factors including light intensity and solar color temperature were assessed as influences on outdoor thermal comfort perception, without measuring body temperature regulation or time of day.