Living in the Dark: What Light Might Be Doing to the Mind

I have a habit of keeping my room dark. Not dim in the cozy, intentional sense. Genuinely dark, sometimes for almost the entire day. The curtains stay closed, the main light stays off, and a screen becomes the brightest object in the room. After enough hours, the arrangement stops feeling unusual.

There is one particular light I switch on for video calls. It makes my face visible, which is its stated job. But I began to notice something else. When it came on, my mood seemed to move with it. The change wasn't dramatic. I didn't become a different person or suddenly feel happy. The room simply felt more available, and I felt a little more available inside it.

I remember something similar from university. I could spend several days in a dark room and then stay at a friend's place, where life seemed brighter and more open. I felt as though I could think more clearly, or see life more clearly and brightly. It was a strange contrast.

Until then, I had never seriously considered light as something that might influence my mental state. It was either present or absent, useful when I needed to see, annoying when I wanted to sleep. The repeated shift made me wonder whether living in a dim environment for long periods could affect mood, alertness, cognition, sleep, or general wellbeing.

My experience was the reason for the question. It wasn't evidence for the answer.

What light is doing

Light entering the eye does more than produce vision. A small class of retinal cells contains melanopsin, a photopigment involved in detecting environmental light. These cells send signals to areas including the suprachiasmatic nucleus, the brain's central circadian clock. Together with input from rods and cones, this pathway helps the body coordinate daily rhythms in sleep, wakefulness, temperature, and hormone release (Hattar et al., 2002).

Melatonin is one marker of that timing. It usually rises in dim conditions during the biological evening. Light at night can suppress that rise or shift it later. The effect depends on when the light appears, how long it lasts, its intensity and spectrum, what light someone encountered earlier, and the person themselves. In one controlled study, sensitivity to evening light varied by more than an order of magnitude between participants (Phillips et al., 2019).

So brightness isn't simply good or bad. Timing changes what it does. Light during the day can support alertness and help anchor the circadian system. The same light late in the evening can make someone feel alert while delaying the body's preparation for sleep.

Ordinary artificial light counts. In a study of 116 adults, room light below 200 lux during the eight hours before bed delayed melatonin onset in nearly every participant and shortened melatonin duration by about 90 minutes compared with very dim light (Gooley et al., 2011). This doesn't mean every lamp will ruin sleep. It shows that indoor light can be biologically meaningful even when it looks unremarkable.

The pattern I had created in my room now seemed more relevant than darkness alone. My days could be extremely dim, while screens remained bright late into the night. That weakens the difference between day and evening. An expert consensus on indoor light recommends the opposite pattern for healthy adults: more light during the day, less in the evening, and darkness during sleep (Brown et al., 2022). It is a general recommendation about circadian physiology, not proof that my own schedule had been disrupted.

What the research can and can't tell me

The evidence closest to my actual question is thinner than I expected. Researchers have studied short exposures in laboratories, lighting in workplaces, light therapy, and light at night. Far fewer studies have followed healthy people living for weeks or months in persistently dim homes. A systematic review of home lighting found only 28 eligible studies across natural light, artificial light, sleep, and physical and mental health. The methods were too varied to support a simple conclusion about what prolonged dimness does to a person (Osibona, Solomon and Fecht, 2021).

The evidence is firmer for alertness. A meta-analysis of 29 experiments found small improvements in subjective and objectively measured alertness under light interventions, although the studies differed considerably (Xu and Lang, 2022). A separate systematic review of daytime electric light found some benefits for reaction time and simple tasks, but results for memory, problem solving, and other higher cognitive functions were inconsistent (Siraji et al., 2022).

That distinction matters because “thinking clearly” is not a precise scientific outcome. A study can measure reaction time, attentional lapses, working memory, errors, or sleepiness. Those may contribute to the feeling of clarity, but none completely captures it.

One small randomized crossover study felt unusually close to my observation. Sixteen sleep-restricted adults worked under low ambient light, then under the same room lighting supplemented by an LED task lamp. With the lamp, they performed better on attention and arithmetic measures and reported better alertness, mood, and motivation. Other measures, including declarative memory and overall mood disturbance, didn't change (Chinoy et al., 2023). It shows that a daytime lamp can produce measurable short-term effects under specific conditions. Sixteen tired people in a simulated workday still can't tell me what years in my bedroom did.

Bright-light therapy provides stronger evidence that carefully timed light can influence mood in clinical settings. A 2025 meta-analysis found that adding bright-light therapy improved response and remission rates in nonseasonal depressive disorders across 11 randomized trials (de Almeida et al., 2025). But a therapeutic light box, often delivering around 10,000 lux on a schedule, is not an ordinary household lamp. These trials don't show that a dark room causes depression, or that turning on my video-call light treats it. They show that light can affect mood-related symptoms when it is used as a controlled clinical intervention.

There may also be a simpler, more immediate explanation. When I turn on the light, the room itself changes. I can see its boundaries, surfaces, and depth. Lighting experiments have found that the amount and distribution of light can alter how spacious, clear, pleasant, or relaxing a room feels (Durak et al., 2007). That is an effect on perception, not evidence of improved mental health. Still, it gives some substance to my memory of life feeling more open. A brighter room may feel like a different place even before any circadian mechanism enters the explanation.

The problem with my observation

My friend's place contained much more than different lighting. It contained a friend. I was leaving my usual environment, moving around more, perhaps going outside, using my screen less, and following a different sleep schedule. The room had another layout, temperature, noise level, and set of associations. There was novelty, social interaction, and a break from isolation. Any of those could change how I felt. Several probably changed together.

The video-call light is no cleaner as evidence. I turn it on because I'm about to speak with someone. The light arrives with anticipation, conversation, a change in posture, and the feeling that I need to become presentable. It may also have become a learned signal that I'm leaving one private state and entering a more social one. Perhaps I remember the calls when the shift was noticeable and forget those when nothing happened.

This doesn't make the experience unreal. It changes what I can reasonably claim about it.

I can say with confidence that light entering the eyes participates in circadian timing, that evening indoor light can affect melatonin, and that brighter daytime light can improve alertness in some controlled settings. I can say that lighting changes the way a room is perceived. I can also say that direct evidence on long-term dim residential environments is limited, and that the research doesn't establish dim rooms as a cause of depression, cognitive impairment, or low motivation.

What remains is a plausible mixture. Some of what I noticed may have been alertness. Some may have been the room looking larger and less closed. Some may have come from sleep timing, social contact, movement, or simply leaving a place where I had settled into a particular state of mind. I can't separate those explanations by looking backward.

Back in the room

The evidence doesn't prove that my dark room was making me feel worse. It has changed how I understand the light switch.

When that particular light comes on, it may be doing several ordinary things at once. It reaches biological systems that care about time and wakefulness. It changes the room I can see. It marks the beginning of a conversation. None of these explanations needs to be dramatic for the small shift I feel to be real.

I used to think of light as background, something that let me see the environment without really being part of it. Now I think the amount and timing of light may be one of the ways a room participates in our experience of being there. Whether lighting alone explains what I felt at university, or what I still notice before a video call, remains uncertain. But the room is no longer just a container for that experience. Its darkness, and the moment it changes, are part of the question.

References

Hattar et al. “Melanopsin-containing retinal ganglion cells”, Science, 2002.
Phillips et al. “High sensitivity and variability in the circadian response to evening light”, PNAS, 2019.
Gooley et al. “Exposure to room light before bedtime suppresses melatonin onset”, JCEM, 2011.
Brown et al. “Recommendations for indoor light exposure”, PLOS Biology, 2022.
Osibona et al. “Lighting in the home and health”, IJERPH, 2021.
Xu and Lang. “Alerting effects of light in healthy individuals”, Neural Regeneration Research, 2022.
Siraji et al. “Effects of daytime electric light on alertness and cognition”, Frontiers in Psychology, 2022.
Chinoy et al. “Task lighting improves daytime alertness and cognitive performance”, Sleep, 2023.
de Almeida et al. “Bright light therapy for nonseasonal depressive disorders”, JAMA Psychiatry, 2025.
Durak et al. “Impact of lighting on impressions of a room”, Building and Environment, 2007.