Last Updated on August 20, 2026 by Rob Cashman
Folklore, classic stories, and modern memes repeatedly place monsters and other frightening creatures in the nighttime.
From what we observe, nighttime (when the Sun goes down and darkness covers the Earth) is where predators lurk, where criminals commit their crimes under the canopy of darkness — hidden from view, hidden from detection. But what properties of night have caused all societies across time to attribute negative traits to darkness and night, even creating spooky campfire stories of the ‘hidden aspects’ of night where ‘the monsters come out’? The missing variable is that darkness changes not only what is illuminating the world around us, but also how our own visual system is able to process the information that remains.
Darkness is typically described as the ‘absence of light’.
Light illuminates; it allows us to see clearly and discern one object from another. It allows us to see colors, shapes, and details in high resolution clarity. When it is ‘sunny’ outside (meaning, when the ‘Sun’ is apparent outside in the sky), we can see details about the world around us.
When it is ‘dark’ outside, we don’t see the world around us as well. The lack of light causes our vision to dim, and to be no longer able to see objects in full color and full resolution as we would in the daylight. In the nighttime, we are unable to discern relationships between objects because our ability to see everything around us is not as strong as it is during the day. At night, the surface also typically cools because it is no longer receiving the Sun’s incoming energy while it continues to lose energy through thermal radiation.
Temperature, and how it relates to light or darkness
Illumination affects us not only by changing what we are able to discern, but it also empowers us to act, move, and create. Just as the nature of fire is to separate what is desired from the waste (which is left as ash), so too the ‘heat’ of the Sun allows us to make use of that energy.
The coincidence that ‘light’ is associated with ‘heat’ (and with it, the ability to act, sort, or discern) gives us a second analogy that occurs concurrently when we encounter daylight.
Darkness, on the other hand, is typically described as being colder, possibly wet, and slow; less is able to be discerned, and less is able to be done with it.
Time, and how it is described through light or darkness
Borrowing the temperature analogy of ‘light’ and ‘dark,’ these concepts also appear metaphorically in the way humans describe periods of history. The term ‘Dark Ages,’ although now considered an overly simplistic description of the European Middle Ages, reflects the metaphor of darkness as ignorance, limitation, or diminished knowledge.
Centuries later, the ‘Enlightenment’ similarly used light as a metaphor for reason and knowledge. The interesting point is not whether these historical periods were literally dark or illuminated, but that humans repeatedly use the physical experience of light and darkness to describe what they believe is happening intellectually.
The Science of Illumination: How Light vs. Dark Affects Us
The absence of light literally means that there is an absence of illumination. “Darkness,” or “night” simply means that light (e.g., from sunlight, or even from a small flame or candle) is no longer illuminating the world around us.
Literally, nighttime too can also be described as the ‘absence of illumination’ from the Sun, where Earth continues its daily rotation, and where the Sun appears to us as if it has descended below the horizon. As we move from daytime, through twilight, and into night, the apparent color of the sky can change dramatically — often passing through shades of blue, pink, orange, purple, and eventually very dark blue or black.
How Illumination Changes What We See
We don’t perceive color as an intrinsic label attached to an object. Our perception of color arises from the interaction between the illumination, the object’s material properties, and our visual system.
When we look at the color “red” in daylight, for example, on a bright red car passing by us, we are told growing up that “the color we are seeing is actually the only color that is not being absorbed by that object; the color we see is the color that is reflected by that object.” This is a useful simplification, but it is not fully accurate.
When we see an object that appears to be red, what we are observing is the result of an interaction between the light illuminating the object, the material properties of the object, and our own visual system. The pigments on the car preferentially absorb some wavelengths while scattering or reflecting others toward our eyes. Our visual system receives that resulting pattern of light and interprets it as the color red.
In other words, when we say “the car is red,” we are describing how that object appears to us under a particular illumination, rather than suggesting that the word “red” exists as a simple label embedded inside the object itself.
Color, therefore, is not something we experience directly from the object. It is something our visual system constructs from the interaction between light, matter, and our eyes.
Colors as a Reflection of Wavelengths of Light
When we look up into the sky, the sky itself does not emit the blue light we perceive from it; in the absence of sunlight scattering through the atmosphere, the sky would appear dark. But light rays from the Sun interact with particles in the sky and with the ‘atmosphere’ itself, causing ‘scattering’ of the Sun’s rays. This affects the wavelengths of light that appear to us, and by extension, it alters the apparent color of the light as it reaches us. The sunlight emitted by the Sun has not suddenly changed; rather, the atmosphere changes which portions of that sunlight reach our eyes, and from which directions.
When I was younger, my mother told me “the sky is black, but it appears to us as blue because it is reflecting the color of the ocean.” For many years, I wondered how the ocean that was over there can affect the sky that we see here.
Rather, the reason the sky appears to us as blue is a result of what happens when the Sun’s rays interact with the Earth’s atmosphere. The Sun produces a huge spectrum of electromagnetic radiation; some of this enters our Earth’s atmosphere. Molecules in the atmosphere (particularly, nitrogen and oxygen) scatter shorter wavelength light across the sky much more efficiently than they would longer wavelengths (which would cause the sky to appear as red).
This is why Earth’s daytime sky appears blue, while the different atmospheric conditions on other planets can produce very different apparent sky colors. On Mars, for example, the daytime sky typically appears as orange or reddish, while sunsets can appear distinctly blue when near the Sun.
As the Sun sets, Earth’s rotation changes the angle at which sunlight reaches us. The same sunlight that once caused us to see the sky as blue needs to travel through a much longer path through the atmosphere before reaching our eyes, changing the apparent color of the sky. As the available visible signal decreases, our perception eventually shifts from the colored illumination of dusk toward darkness—not because “black” is another wavelength, but because insufficient light reaches our visual system to produce the same kind of color perception.
How Colors are Created in Our Minds
To be accurate, there really aren’t colors in light. Our eyes have components (long, medium, and short cones, or L cones, M cones, and S cones) that receive the light, and based on the proportion of light that each component contains, it is our brains that translate this into color.
The three major types of cones are:
- L cones — preferentially sensitive to longer wavelengths
- M cones — preferentially sensitive to middle wavelengths
- S cones — preferentially sensitive to shorter wavelengths
Although red, green, and blue are commonly called the primary colors in additive color systems, the three cone classes are not simply ‘red cones,’ ‘green cones,’ and ‘blue cones.’ The sensitivity curves of each of these cones overlap substantially, and the colors we perceive are the result of our brain comparing their responses.
We don’t experience wavelengths of light directly. Rather, our nervous systems receive patterns of differential activation, and from that we construct our color perception from these.
Thus, for illustration purposes only, a particular spectral distribution might produce:
L cones = relatively high
M cones = moderately high
S cones = relatively low
and our brains would interpret that pattern as a particular color. So it would be misleading to say that ‘the photon is red.’
A photon has a wavelength (or, more precisely, a frequency/energy); ‘red’ is a perceptual experience produced by our visual system in response to patterns of light.
And because human color vision depends on the relative responses of three major classes of cones, the proportions of different wavelengths reaching those cones help determine the colors we perceive. Seeing color as combinations of Red, Greed, and Blue is one useful way of representing color, but it is not the same thing as the biological mechanism by which the eye constructs color.
The colors that we see on an object do not describe the color of that object; they describe how that object interfaces with light.
Human Perception is Based on 3 Types of Vision Contained Within the Human Eye.
There are three functional regimes within the human eye, or ‘modes’ that we use to see the world around us. Simplifying a bit, we have 1) Photopic vision (primarily cones, for use in the day), 2) Scotopic vision (primarily rods, for use at night), and 3) Mesopic vision (a combination of cones and rods). Each type of seeing has a particular set of abilities, but they also contribute to the psychological meaning we give to day or night.
For clarification, while I am referring to them as “modes,” these aren’t three ‘types’ of seeing. Moving from one ‘mode’ to another is NOT the same as ‘shifting gears’ as we would when driving a car.
Rather, receiving light from the Sun (and other sources) provides us with a particular ‘radiation environment,’ and these three regimes help explain the different relationships between cones and rods that we use to understand the world around us (based on the type of light we are experiencing).
Mode #1: Photopic Vision (Primarily “Cones” used for Discernment During Daylight)
With Photopic vision, our eyes primarily use cones to see the world around us. These cones allow us to see colors, fine spatial resolution, detail, to adjust to rapid changes, and to make precise discrimination between objects in the world.
But to function, these cones require high levels of illumination. This is why ‘daylight’ vision is very information-rich. With cones, we can discern the slight difference between colors, and we can identify textures, and edges. With sufficient illumination and visual acuity, we can detect fine facial movements and subtle differences in expression that may be difficult to perceive under low-light conditions.
So too, photopic vision allows us to focus in and discern the boundaries and distinctions within the field of illumination.
Mode #2: Scotopic Vision (Primarily “Rods” used for Night Vision)
With Scotopic vision, our eyes primarily make use of rods to see when there is darkness, because rods are significantly more sensitive to low levels of light.
Rods give us different capabilities than cones do. Because there is less light available for us to make use of, we have a diminished ability to distinguish between colors. However, rods have a superpower.
In darkness, we can still detect things, but we have less information with which to determine exactly what those things are.
In daylight, we would be able to use cones to discern and describe what is there. If we saw a strange shape in broad daylight, we would be able to inspect it. We would distinguish its edges, determine its color, its texture, its size, its position, and its relationship to surrounding objects. If it had a face, we could even determine its facial expression to determine if it is hostile or not. But at night, we do not have this ability.
At night, our visual system shifts to perceive and process what we see using rods.
Rods don’t literally tell us “something is there.” Rather, because they are highly sensitive to low levels of illumination while providing much less spatial and color information than cones, and the information reaching our brains at night is often sufficient to detect something without providing enough detail to identify it confidently.
There is an additional oddity: rods are especially abundant outside the central fovea, while the fovea is densely packed with cones. This means that in very dim conditions, something faint may sometimes be easier to notice when it is slightly off to the side than when we stare directly at it.
Thus, at night, the rods may still give us enough information to detect that “something is there.” If it moves, the rods might help us detect that “something moved.” We might even be able to identify a rough shape in the darkness, but rods wouldn’t give us enough spatial and color information to be able to determine, “I know what that thing is.”
And that gap between presence and identification is where the monsters live.
Mode #3: Mesopic Vision (or, where rods and cones both contribute).
Mesopic vision occurs in intermediate illumination — precisely the kinds of conditions we encounter around dusk and dawn. Both cones and rods contribute to our vision during this time, so the transition is not like a digital ‘on / off’ switch, but rather, an analog transition (like a knob selecting a radio station) where the two systems overlap.
Dusk and dawn are familiar examples of mesopic conditions. Standing outside, we are able to make use of the differentiation abilities that the cones provide us, and the sensitivity of ‘what is present’ that the rods provide us.
So dawn allows us to experience at least three simultaneous transitions:
1) The environment is changing (more solar radiation begins reaching the atmosphere visible to our eyes),
2) The atmosphere affects the radiation coming from the Sun, altering the spectrum and intensity of light reaching us, and
3) Our own visual system moves progressively from predominantly scotopic conditions, through mesopic conditions, toward predominantly photopic vision.
Thus, experiencing sunrise is not merely ‘seeing the Sun come up’. Rather, we experience the relationship between the source of light (the Sun), the radiation field (that the Sun gives off), the atmosphere (the barrier that shields us from the Sun and filters or modifies the light that we receive). Most of all, we ourselves change as we move through this experience (by changing from a scotopic -> mesopic -> photopic vision).
Why the Biological Makeup or Our Eyes is Relevant to How We Interact With the World
It is noteworthy that human eyes have these different methods of seeing. This feature alone does not demonstrate that we are more advanced or superior to other animals, as there are animals whose eyes are significantly more specialized than ours. Some can see wavelengths that are outside a human’s field of vision.
The fact that our eyes contain these different ways of seeing raises another interesting question: why do we have them? I suppose from this biology, we can make inferences as to what our purpose is, answering the universal question, “Why are We Here?” We can also come up with possible reasons about animals and other organisms, answering the question, “Why are They Here?”
Returning to the differences between light (daytime) and dark (nighttime), with the understanding of what happens as the Sun sets, we gain a deeper understanding of ourselves and the world around us.
Darkness can still be described physically as the absence—or severe reduction—of visible illumination. But from the perspective of perception, darkness means something more: the available visual signal has fallen below the levels at which our visual system can extract the same kinds of information it extracts in bright light.
Most interestingly of all, because at night we have a different set of senses which allow us to perceive merely whether an object or an entity is present or not, or whether it moved. We don’t have the abilities that we would have during the day. Perhaps this helps explain why so many human stories place monsters, spirits, and mysterious beings in darkness.
So do Monsters Only Come Out at Night?
With this new understanding, if there were such a thing as monsters, nighttime would be a much better setting for us to mistake them for something mysterious.
During the day, our cone-dominated vision would give us far more information with which to identify whatever we were seeing. At night, our rod-dominated vision may allow us to “notice movement,” or “detect the presence of something,” without giving us enough information to determine exactly what we are seeing.
This does not mean that monsters exist, but this does explain that if they do, why we have only seen them at night. Thus, all the spooky stories happen “at night, under the cover of darkness.” Could they exist during the day? Of course. But if they were visible in daylight, our cone-dominated vision would give us far more information with which to identify them. At night, our rod-dominated vision may allow us to notice movement or detect the presence of something without giving us enough information to determine exactly what we are seeing.
Perhaps if monsters do exist, because of the way our sleep cycles work, maybe we were not meant to see them. Humans are primarily diurnal rather than nocturnal, so our visual system evolved in a world where detailed vision was most useful during daylight, while our rod-dominated system allowed us to remain capable of detecting movement and navigating when illumination was low.
If there was one exception, perhaps, it would only be those of us that rise at dawn, or sit outside at dusk — those people might not only be able to ask the question, “is something there?” but also to observe what ‘it’ looks like.
In the end, it is not the darkness that changes whether what we perceive is there or not, but rather, what we are capable of knowing about what is there.