1. Why Does Your Vision Look Red or Orange When You Close Your Eyes Facing a Window?
When you face a daytime window and close your eyes, your field of view is not black. It is a color close to red or orange. This happens because light from outside passes through your eyelids and reaches your retina [3]. The skin of the eyelid is thin and has many blood vessels inside it. One explanation is that light passing through the eyelid takes on the color of blood, making it look red [3]. Another reason given is that eyelid tissue lets red wavelengths pass through well but blocks blue wavelengths [3]. This is one way to explain why the view looks red. How much of each color passes through has been checked in studies. The next section looks at those numbers.
2. How Much Light Passes Through Your Eyelids, and Why Do Measurements Differ?
One study reported percentages for each color of light passing through eyelids. For red light (wavelength 630 nanometers, where wavelength is a guide for color), about 9% passed through. For green light (550 nanometers), about 0.5% passed through. For blue-green light (490 nanometers), about 0.4% passed through [1]. If you calculate 9 divided by 0.5 using the values from this report, red is about 18 times more likely to pass through than green.
Professor Hideki Sakai at Osaka Metropolitan University and his team measured the "effective transmittance" for 33 people when they closed their eyes. The average was 52.4% for red, 26.2% for yellow, 21.6% for green, and 4.5% for blue. For white light, it was 42.7% [2]. In this study too, red passes through the most and blue the least. If you divide red by blue using the averages from this study, the result is about 11.6 times.
The numbers differ because the studies measured different things. Professor Sakai’s team reported that their values are up to about 10 times higher than previous reports, and there are large individual differences [2]. Effective transmittance is based on how bright people feel it is, so it is different from the physical transmittance of the eyelid. Therefore, you cannot simply line up these two sets of numbers and decide which one is "correct." What is clear is that in both studies, red passes through the most, and blue and green pass through less. So, what color is the view when you close your eyes in a dark room where almost no light passes through?
3. Why Do You See Dark Gray Instead of Black With Eyes Closed in a Dark Room?
Even if you close your eyes in a dark room with the curtains drawn, you do not see complete black. It is often explained that you see a dark gray haze [4]. This uniform dark gray seen in low-light places is called "eigengrau" [4]. This gray looks slightly brighter than a black object viewed in a well-lit room. [Delete this sentence.] However, this name alone does not explain why it feels dark when you close your eyes. To understand this, we must look at what is happening inside the eye. How the retina creates signals in darkness
4. How Can Heat Make Rhodopsin in the Retina React Without Light?
The retina has photoreceptor cells that catch faint light in dim places. One type is the "rod" cell. Inside rod cells, there is a molecule called rhodopsin that receives light. Even in total darkness, rhodopsin can react naturally due to heat. The signal from this reaction cannot be distinguished from a signal caused by a real photon (a particle of light) [4]. Because there are many rod cells in the retina, there is a possibility that these small signals overlap.
In 1980, Baylor and others examined electrical fluctuations (dark noise) in the rod cells of toads in darkness. They showed that discrete signals within this noise are caused by the natural activation of a single rhodopsin molecule by heat [5]. This size matches the "dark light" that Barlow proposed in 1956 to explain the statistics of human vision adapted to darkness [5]. In other words, it is thought that even in complete darkness, the retina sometimes creates signals that look like light. So, does the retina create light signals even from non-light stimuli?
5. Why Do You See Light When You Press Your Eyes? Phosphenes and the Retina
The sensation of seeing light or patterns when no light is entering the eye is called "phosphenes." This can happen with stimuli other than light [6]. The MSD Manual also explains that this can happen when you rub your eyes [8]. This phenomenon has been known for a long time. It is reported that Newton recorded seeing colored rings of light on the opposite side when he pressed his eyes with a finger. Ancient Greek literature also describes light seen when pressing the eyes [6].
In 1989, Grüsser and others conducted an experiment deforming the eyeball in darkness. They found that "on-center" retinal ganglion cells became active, while "off-center" cells were suppressed [7]. On-center cells are the type that react strongly when light hits them. The pressed retina showed a reaction similar to when light arrives. If you see light frequently without rubbing your eyes, or if it suddenly increases, you are advised to consult an ophthalmologist [8]. Note that Newton’s own description is introduced through secondary sources, so it is safe to read it as "it is reported that."
6. How Can You Compare What You See With Eyes Closed at a Window and in a Dark Room?
All you need to do is With an adult’s help, compare what you see in these three situations. Do not face the sun or a very bright light, even with your eyes closed. First, face a daytime window, close your eyes, and describe the color you see (do not look directly at the sun). Second, turn your back to the window, close your eyes, and compare how the brightness changes. Third, make the room as dark as possible, close your eyes, and compare the color and brightness to the first situation. How do the color and brightness change depending on the direction of the window and the room's brightness? Putting your experience into words helps you compare it with the numbers and explanations in this article. Do not rub or press your eyes. If you see light frequently without rubbing, or if it suddenly increases, you are advised to consult an ophthalmologist [8].