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Are you afraid of the dark?

Apparently, the answer is no. You aren’t afraid of the dark; you’re afraid of the night. A team of researchers from the Ministry of Education and Southwest University in China wanted to know what was the difference between “night” and “darkness” in the context of fear, so they asked participants to rate their fear during the day versus the night under light and dark conditions(1). Participants were randomly presented with fear-inducing sounds, like screams or creaky doors, and spooky images like spiders or violence. The researchers also measured skin conductance and heart rate to gauge the physiological response to fear. The participants had a greater physiological response (think racing heart, sweaty palms) and rated the fear-related materials as scarier during the nighttime condition compared to the day. Just turning the lights off did not cause the same increase in fear.

Of course, you don’t need a research study that sounds like a scene from Clockwork Orange to tell you that things are scarier at night. Haunted houses are not known for their matinee shows. The fact that the circadian rhythm influences emotional perception may have implications for safety. SAFTE-FAST accounts for the circadian rhythm (the human biological concept of time) when estimating fatigue risk. Even when an individual is fully-rested, their reaction times will be slower during the night or if they are jet-lagged. This allows organizations to prospectively analyze the risk associated with night shifts or travel crossing multiple time zones. What organizations may not be taking into account though is the increased spookiness of working at night. This phenomenon is particularly relatable in the context of driving.

“Road rage” gets the most attention when discussing the negative influence of emotions on driving ability, but the truth is that any strong emotion can impact decision-making. Anger on the road can lead to an underestimation of risk and making more errors than usual. Fear, on the other hand, may cause drivers to overestimate risk or workload(2,3). Darkness/driving at night also contributes to vehicle accident risk(4-6). Taken together, it’s no wonder that horror movies frequently feature car chases at night: Understanding the interplay between human emotion and driving skills isn’t just in the domain of filmmakers; it’s also a target for computer scientists trying to design intuitive on-board computers systems like we may see in self-driving cars someday. Ironically, Christine is a movie about a self-driving car who plays on human emotions that is second on the above list of scary films.

Another thriller that does a good job of exploring the concept of fear and anger while driving is Spielberg’s 1971 classic Duel. This movie is presented from the point of view of a driver who is terrorized by a tanker truck after cutting the truck off in traffic earlier. Dennis Weaver plays the protagonist who becomes increasingly jittery over the course of the movie. The truck driver is never shown but he must have had a serious case of road rage in order to follow Weaver for a runtime of 1 hour 31 minutes. The moral of the story is that emotion on the road is a safety hazard. Interestingly, Duel is marketed as an action movie rather than a horror movie despite having a similar premise to the scary movies on the list above. Duel may be less scary than Christine or The Car because it takes place during the day. The plot would be much more frightening at night.

Professionals who regularly work at night might be less inclined to get the heebie-jeebies after sunset. No one has directly studied the prevalence of nyctophobia (fear of the dark) or differences in fear perception at night in adult shift-working populations. As it stands, more research needs to be done to understand the influence of time of day on fear responses in humans at all. It has been hypothesized that the circadian rhythm plays a role in memory encoding for fear-related or traumatic experiences(7). In other words, someone may be more likely to remember a nighttime event as traumatic, which would have implications for developing post-traumatic stress disorder (PTSD). Sleep is related to PTSD risk as well(8,9). Getting good sleep consistently could perhaps protect against developing symptoms of post-traumatic stress.

The goal of this post is not (just) to scare the reader. Night work is associated with human factors risks like sleep disturbances and circadian disruption. Biomathematical modeling tools like SAFTE-FAST can help organizations take these risks into account. But a well-designed fatigue risk management system (FRMS) is more than just understanding the biological underpinnings of fatigue. Risk management should acknowledge the social and emotional impact of working nights on human operators as well. Also, it’s probably a bad idea to keep a collection of horror movies in the company breakroom.


1. Li Y, Ma W, Kang Q, et al. Night or darkness, which intensifies the feeling of fear? International Journal of Psychophysiology. 2015; 97 (1): 46-57

2. Lu J, Xie X, Zhang R. Focusing on appraisals: How and why anger and fear influence driving risk perception. Journal of safety research. 2013; 45: 65-73

3. Jeon M, Yim J-B, Walker BN. An angry driver is not the same as a fearful driver: effects of specific negative emotions on risk perception, driving performance, and workload. In: proceedings from the Proceedings of the 3rd international conference on automotive user interfaces and interactive vehicular applications; 2011.

4. Fotios S, Robbins CJ, Uttley J. A comparison of approaches for investigating the impact of ambient light on road traffic collisions. Lighting Research & Technology. 2021; 53 (3): 249-261

5. Raynham P, Unwin J, Khazova M, Tolia S. The role of lighting in road traffic collisions. Lighting Research & Technology. 2020; 52 (4): 485-494

6. Herd DR, Agent KR, Rizenbergs RL. Traffic accidents: Day versus night. 1980;

7. Albrecht A, Stork O. Circadian rhythms in fear conditioning: an overview of behavioral, brain system, and molecular interactions. Neural plasticity. 2017;

8. Maguire DG, Ruddock MW, Milanak ME, Moore T, Cobice D, Armour C. Sleep, a governor of morbidity in ptsd: a systematic review of biological markers in PTSD-related sleep disturbances. Nature and Science of Sleep. 2020; 12: 545

9. Germain A, McKeon AB, Campbell RL. Sleep in PTSD: Conceptual model and novel directions in brain-based research and interventions. Current opinion in psychology. 2017; 14: 84-89


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