question: Is it better for your eyes to have a phone brightness set low or high when it's night (pitch black), and why?
comment: Better to set it to low. Your eyes use blue light (light of the sky) to synchronize the body's internal clock. Blue light means daytime which means you should stay awake. Our digital devices nowadays produce a great deal of blue light. The more blue light exposure at night you get, the more your body's internal clock gets confused, causing you to have worse sleep at night. High brightness will also cause your eyes to lose dark sensitivity at night. If you stare at something bright for a long period of time, you'll notice that you won't be able to see well in dim lighting. This recovers in ~20-40 minutes in darkness and is known as dark adaptation. If you find yourself taking a long time to adjust to darkness, go see an eye doctor as this is a symptom of eye disease.
passages: Phone boxes or telephone booths are prominent in most cities. While they range drastically in the amount of cover they offer users (e.g. many only cover the phone itself while others provide full booths) they are typically easy to spot. The widespread use of mobile phones has resulted in a decrease in their numbers.
  
  Streetlamps are designed to illuminate the surrounding area at night, serving not only as a deterrent to criminals but more importantly to allow people to see where they're going. The colour of streetlamp bulbs differ, but are generally white or yellow.
   The non-profit Lighting Research Center, a group of utility companies, experts and government agencies, established the National Lighting Product Information Program (NLPIP) in the USA to provide objective information about the effectiveness of different lighting systems. According to the NLPIP, full-spectrum light does not provide any improved benefits over similar light systems.
  
  A Cornell University study reached mixed conclusions on the use of full-spectrum lighting in restaurants to promote sales.
   Whether it is easier or healthier to read text on a dark background was disputed by vision and perception researchers; there was similar dispute between users. However, a recent article by "Popular Science" suggests that "Dark mode is easier on the eyes and battery"
  
  Section::::Energy usage.
  
  Light on dark color schemes require less energy to display on some display technologies, such as OLED, CRT and LCD displays. This can impact battery life and overall energy conservation.
   Street lamps can be used to display advertisements for nearby businesses or attractions on cellular devices as an individual passes through. A customer walking into a store and passing through the store's front lights can show current sales and promotions on the customer's cellular device.
  
  Section::::Applications.:Education.
   Since tactical lights are intended for use in situations where lethal force is likely to be used, reliability is important.
  
  Section::::Lighting features.:Battery.
   Exposure to light during traditional sleeping hours have are
  
  documented to cause disruptions in the circadian rhythm that regulate human
  
  sleep cycles. Biologists have noted a decrease in the amount of melatonin, a natural hormone that regulates the Circadian rhythm, in humans that are exposed to light pollution of the night sky. In order to prevent major impact, biologists suggest to increase the amount of natural light exposure during the day and decrease the amount of electrical light consumed at night.
  
  Growth patterns of plants and trees:
  
  The growing pattern of trees have been disrupted and less adjusted to seasonal
   There are Orthodox Jewish religious restrictions which, by some interpretations, standard mobile telephones overstep. To deal with this problem, some rabbinical organizations have recommended that phones with text-messaging capability not be used by children. Phones with restricted features are known as kosher phones and have rabbinical approval for use in Israel and elsewhere by observant Orthodox Jews. Although these phones are intended to prevent immodesty, some vendors report good sales to adults who prefer the simplicity of the devices. Some phones are approved for use by essential workers (such as health, security, and public service workers) on the sabbath, even though the use of any electrical device is generally prohibited during this time.
   The daytime running light was first mandated, and safety benefits first perceived, in Scandinavian countries where it is persistently dark during the winter season. As ambient light levels increase, the potential safety benefit decreases while the DRL intensity required for a safety improvement increases. The safety benefit produced by DRLs in relatively dark Nordic countries is roughly triple the benefit observed in relatively bright United States.
  
  Section::::Effect on motorcycle safety.
   A more recent discussion (2009), written by Professor Steven Lockley, Harvard Medical School, can be found in the CfDS handbook "Blinded by the Light?". Chapter 4, "Human health implications of light pollution" states that "... light intrusion, even if dim, is likely to have measurable effects on sleep disruption and melatonin suppression. Even if these effects are relatively small from night to night, continuous chronic circadian, sleep and hormonal disruption may have longer-term health risks". The New York Academy of Sciences hosted a meeting in 2009 on Circadian Disruption and Cancer. Red light suppresses melatonin the least.
   Some frequent travelers carry small nightlights for temporary installation in their guestroom and bathroom, to avoid tripping or falls in an unfamiliar nighttime environment. Gerontologists have recommended use of nightlights to prevent falls, which can be life-threatening to the elderly.
  
  The low cost of nightlights has enabled a proliferation of different decorative designs, some featuring superheros and fantastical designs, while others feature the basic simplicity of a small luminous disc.
  
  Section::::Light source and variants.
   In the effort to reduce light pollution, researchers have developed a "Unified System of Photometry," which is a way to measure how much or what kind of street lighting is needed. The Unified System of Photometry allows light fixtures to be designed to reduce energy use while maintaining or improving perceptions of visibility, safety, and security. There was a need to create a new system of light measurement at night because the biological way in which the eye's rods and cones process light is different in nighttime conditions versus daytime conditions. Using this new system of photometry, results from recent studies have indicated that replacing traditional, yellowish, high-pressure sodium (HPS) lights with "cool" white light sources, such as induction, fluorescent, ceramic metal halide, or LEDs can actually reduce the amount of electric power used for lighting while maintaining or improving visibility in nighttime conditions.
   As the market increases to grow, more light is being shed upon the accompanying behavioural health issues and how mobile phones can be problematic. Mobile phones continue to become increasingly multifunctional and sophisticated, which this in turn worsens the problem.
  
  According to optician Andy Hepworth, blue violet light, a light that is transmitted from the cell phone into the eye is potentially hazardous and can be "toxic" to the back of the eye. He states that an over exposure to blue violet light can lead to a greater risk of macular degeneration which is a leading cause of blindness.
  
  Section::::Effects.:Psychological.
   Night Shift is a display mode introduced in iOS 9.3. The mode shifts the colors of the device's display to be warmer, similar to F.lux, a popular program for Microsoft Windows and Apple macOS computers. When enabled, it uses the device's clock and geographic location to determine when to turn the feature on or off. Optionally, the user can set a manual schedule, or not have a schedule at all. For ease of access, there is a new Night Shift toggle in the Control Center. The settings for Night Shift are located under "Display and Brightness" in the Settings app, and on top of enabling the feature and setting a schedule, the user can also set the warmth of the display.
   BULLET::::- Proper cockpit lighting is paramount in reducing fatigue since it inhibits the production of melatonin. Studies have shown that simply increasing lighting level to 100-200 lux improves alertness in the cockpit. 100 lux level is the same as room lighting and, therefore, would not affect a pilot’s night vision.
  
  Section::::Countermeasures.:Alternative strategies.
   Scientists at the University of Michigan have developed a contact lens that can act as night-vision device. The lens has a thin strip of graphene between layers of glass that reacts to photons to make dark images look brighter. Current prototypes only absorb 2.3% of light, so the percentage of light pickup has to rise before the lens can be viable. The graphene technology can be expanded into other uses, like car windshields, to increase night driving abilities. The US. Army is interested in the technology to potentially replace night-vision goggles.
   Using red light for night vision is less effective for people with red–green color blindness, due to their insensitivity to red light.
  
  Many animals have a tissue layer called the "tapetum lucidum" in the back of the eye that reflects light back through the retina, increasing the amount of light available for it to capture, but reducing the sharpness of the focus of the image. This is found in many nocturnal animals and some deep sea animals, and is the cause of eyeshine. Humans, and monkeys, lack a "tapetum lucidum".
   Signify lighting company (formerly Philips Lighting) has developed a VLC system for shoppers at stores. They have to download an app on their smartphone and then their smartphone works with the LEDs in the store. The LEDs can pinpoint where they are located in the store and give them corresponding coupons and information based on which aisle they are on and what they are looking at.
  
  Section::::Home and building automation.
   A system-wide dark mode was implemented, allowing users to enable a light-on-dark color scheme for the entire iOS and iPadOS user interface and all native applications, as well as all supported third-party apps. It can be manually turned on or set to automatically switch between light and dark modes based on the time of day.
  
  Section::::System features.:Siri.
   A well-designed feature phone can be used in industrial environments and the outdoors, at workplaces that proscribe dedicated cameras, and as an emergency telephone. Several models are equipped with hardware functions — such as FM radio and flashlight — that prevent the device from becoming useless in the event of a major disaster, or entirely obsolete, if and when 2G network infrastructure is shut down. Other feature phones are specifically designed for the elderly, and yet others for religious purposes.
  
  Section::::Rationale.
  
  Section::::Rationale.:For manufacturers.
  
  Feature phones are often kept in phone manufacturers' lineups for several reasons:
   For Police S.W.A.T. use, long-range weapon lights with exceptional range have always been a problem. Tactical weapon lighting companies such as ExtremeBeam for example have created small light duty lights which S.W.A.T. officers are able to mount to their modern weapons giving them an extended range out to beyond 300 meters (325+yards). This has allowed officer to blind suspects and protect officers closer at hand from being detected and thereby allowing for a better resolution of the situation with less lethal force.
  
  Section::::Lighting features.
   UN R48 has mandated the installation of automatic headlamp since July 30, 2016. With Daytime running lamp equipped and operated, the dipped beam headlamp should automatically turn on if the car is driving in less than 1,000 lux ambient condition (Automatic switching condition), such as in tunnel and in dark environment. while driving in tunnel or dark environment, Daytime running lamp would make glare more evident to the upcoming vehicle driver, which in turn would influence the upcoming vehicle driver's eyesight, such that, by automatically switching the Daytime running lamp to the dipped-beam headlamp, the inherent safety defect could be solved and safety benefit ensured.
   In the past, Germany, Spain, France and other European countries have encouraged or required daytime use of low beam headlamps on certain roads at certain times of year; Ireland encourages the use of low beam headlights during the winter, Italy, Hungary and Romania require daytime running lamps outside populated areas, and Bulgaria, Czech Republic, Estonia, Kosovo, Latvia, Lithuania, Macedonia, Montenegro, Poland, Serbia, Slovakia and Slovenia require the use of full or reduced voltage low beam headlights at all times. Whether this requirement is met by the DRLs required on new cars since February 2011 is a matter of individual countries' laws.
   Another study has indicated that sleeping with the light on may protect the eyes of diabetics from retinopathy, a condition that can lead to blindness. However, the initial study is still inconclusive.
   In a study done on the effect of lighting intensity on delta waves, a measure of sleepiness, high levels of lighting (1700 lux) showed lower levels of delta waves measured through an EEG than low levels of lighting (450 lux). This shows that lighting intensity is directly correlated with alertness in an office environment.
   The ComfortLight introduced in the Kobo Glo was also present in the Kobo Aura, allowing a user to read in the dark. Battery life was estimated to be up to 2 months, assuming 30 minutes of reading a day and Wi-Fi turned off.
  
  Section::::Software.
  