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Red light is the most suitable light for observing astronomy

News Trade News2021-10-03 01:10:30

I believe that the little friends who have stargazing experience are familiar with the red light as a sharp weapon, which allows your eyes to switch freely between the ground and the sky.

Red headlamp

Red lighting

Observation bases like the Stellafane2 Starry Sky Conference often use weak red light.

The ability to protect the eyes to adapt to the dark environment is crucial for visual astronomers. At this point, they have common needs with pilots, seamen, soldiers and even security personnel. Even pedestrians who move at night will benefit from the absence of "night blindness." But few researchers have studied the damage to vision caused by exposure to a weak light source, or which color of light is the least likely to interfere with the human eye's ability to adapt to the dark.

Red light has always been the traditional lighting color chosen by visual astronomers. It can not only help them travel safely at night, but also can be used to look up star catalogs.

When asked about the reason for using red light, astronomers often explain that our retinal receptors cannot detect red light in the dark, so night vision is immune to red light. Another possibility for astronomers to choose red light may be attributed to the historical factor that red light is often used in photographic darkrooms.

In the June 2016 issue of Sky and Telescope, author Robert Dick believes that from the perspective of visual physiology, for most people, red light is less for visual images, but his test is limited to personal experience. As a doctor who has received postgraduate training in visual physiology, I decided to test his theory.

Crash Course in Visual Physiology

The visual cells behind the human retina-rods and cones, play the role of receptors, and they can convert the received photons into nerve impulses. The response of the two to different colors of light is also different: rod cells are about 1,000 times more sensitive to green light than cone cells, but the two are equally sensitive to red light. Among them, cone cells can distinguish colors under bright light and produce photopic vision, but cannot perceive dim light; rod cells are responsible for providing monochromatic vision in dim light, causing scotopic vision, and bright light will make them very Fast saturation. Between photopic vision and scotopic vision to adapt to the brightness range, the vision that is acted on by cone cells and rod cells at the same time is called intermediate vision.

Rods and cones

Rod and cone receptors have different responses to the spectrum of visible light. The rod system is more sensitive to most colors of light than the cone system. But when the light wavelength exceeds 620nm, the light sensitivity of the two systems tends to be the same.


Red headlamp

In visual astronomy, an important function of the telescope is to collect enough light so that the eyes can work in the state of intermediate vision.

Many observers mistakenly believe that visual astronomy only relies on scotopic vision, but rod cells only provide low-resolution monochromatic vision in peripheral vision. The center of vision falls on the retina called the fovea, which is composed of cones that are closely packed together. Because only here are so many dense cones gathered, which is why only the fovea can perceive visual details. On the other hand, the sensitivity of off-axis vision (also known as afterglow) will decrease by 50% or more with every 1-degree deviation. When it deviates from the central axis by 10°, the observer's vision is even lower than 20% of the central vision. The edge details we perceive are often the result of our brain concocted in the same way.

Therefore, only the cone receptor can see the intricate patterns on the moon or planet, or distinguish two frontal stars that are close to each other; the role of the rod receptor in visual astronomy is basically limited to detecting dim stars that are not in the center of vision Or whether the nebula exists or not. This is why the observer sometimes needs to use the peripheral light to make the image deviate from the visual axis by about 20°, so that the image will eventually fall in the area with the highest rod cell density to observe the nebula more clearly. Not only that, but the sensitive sensitivity of rod cells to green light can weakly enhance the observer's color perception ability.

Dark adaptation

Eyes that are fully adapted to the dark are 500,000 times more sensitive than those that are fully adapted to light. The pupil dilation plays only a minor role in dark adaptation. It can increase the sensitivity of the human eye to light by a factor of 30. The main process of dark adaptation occurs in rod cells and cone cells. Under dark conditions, photochemical substances are continuously depleted and regenerated, and finally self-regulation sensitive to light is completed.

It takes 15 minutes for cone cells to fully adapt to the dark, while rod cells need at least 30 to 40 minutes. In order to distinguish between extremely dim objects and dark backgrounds, the rod receptors are connected to many other rod receptors to generate a common signal and reduce background noise, but it will also cause the vision's sensitivity to the edge area to be further weakened.

Our goal is to find the right combination of intensity and color of the light used during observation, so that the light has the least effect on the dark adaptation of the human eye. For most observers, they need to rely on cone cells to observe details, so the use of red light will bring benefits, because it will adapt to the dark adaptation of red-sensitive cone cells; on the other hand, rod cells are resistant to blue Green light is very sensitive, and this type of color should be the worst color for protecting rod receptors.

It is worth noting that although most people have about 70% of the total number of red cones, researchers have recently discovered that this proportion may be as low as 27% in people with normal color vision. It ranges from as high as 90%. This result indicates that the best color to protect dark adaptation may also vary from person to person.

Red headlamp


The Queensland Astronomical Festival provides an excellent opportunity to test this theory, and we can test it with experienced astronomers in extremely dark conditions.

I conducted a 90-minute test with 15 astronomers in 10 nights. Before the test, I first confirmed that they did not have color blindness, poor eyesight, diabetes, or other diseases within the exclusion criteria, and determined the limit visual astrology of these astronomers.
After the subjects have fully adapted to the darkness, they need to read the optometry chart on the laptop and distinguish these black letters on various colored backgrounds. I measured the brightness of the screen at this time with a illuminance meter. The screen background for testing is red, orange, green, white, and finally bright red. In order to test how reading the graph screen affects their dark adaptation, after 1 to 4 minutes of reading the graph, I re-evaluated their extreme visual magnitude.
The bright Alpha Southern Cross (upper right corner) is full of dust clouds, which form part of the huge dark nebula, the Coal Sack Nebula. The subject’s ability to see the Coal Sack Nebula and the nearby Small Magellanic Cloud indicates the sensitivity of their rod receptors.


The red light screen needs to be three times brighter than the green light screen in order for the subject to read at the baseline visual acuity level. As we expected, the damage caused by green and white light is the most significant; unexpectedly, the damage caused by rods and cones is comparable to the damage caused by green or white screens, which confirms that night vision will affect red Light immunity. Although green light is obviously much darker than other colors, it is the most destructive to the vision of rod cells.

Exposure to a variety of different color screens will result in a unequal drop in the number of stars visible to the human eye, but orange light illumination has obvious advantages in a dark sky; exposure to green light and white light will make the human eye total visible stars count Reduce by about 50%.

Among the 15 subjects exposed to red light, 11 subjects were able to observe the Coal Sack Nebula and the Small Magellanic Cloud, while the number of people who observed the Coal Sack Nebula and the Small Magellanic Cloud after exposure to green light dropped to There are only 6 people. 4 minutes after the eyes are exposed to red and orange light, and within 10 minutes of exposure to green, white or bright red light, the dark adaptation of the eyes can basically be completely restored.
Under different colors of screen light, the screen brightness required by the subjects to read the same test chart is different.

Red headlamp

Although the difference between this conclusion and the existing conclusion is not significant enough, it is also in line with the recommendations of the International Dark Sky Association: using more red light instead of blue light to illuminate the pedestrian area can not only minimize light pollution, but also maximize Ground improves our ability to observe shadow areas outside the illuminated area.

In view of the fact that this discovery will have an impact on many people working in low-light environments, it is absolutely necessary to carry out more extensive and in-depth research. At the same time, I believe this research shows that red light will be the most suitable light for observing astronomy.
The USB rechargeable outdoor LED headlamp is a good headlamp that I think is suitable for observing astronomy. It is a radioactive red light with a lighting time of >12 hours.

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