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--- health:screen-brightness [2019/07/18 21:01]
john [The effect of screen brightness]
+++ health:screen-brightness [2020/04/27 01:48] (current)
marcos
@@ Line 1: / Line 1: @@
-Under construction
-====== The effect of screen brightness ======
-Screen brightness has an effect on Saccades [[https://www.sciencedirect.com/topics/medicine-and-dentistry/saccadic-eye-movement]]. Saccades can easily be defined as rapid shifts in the gaze, that aligns the line of sight (between the two eyes) on the desired object on the screen. They are rapid eye movements that enable us to scan a visual scene.
-{{:health:capture5.png?400 |}}
+====== Screen Brightness ======
+===== Bright Screens are Harmful to Your Eyes =====
-These eye movements depict how the nervous system relates to the repertoire system. In short, the screen brightness of your computer, tablet or phones has an effect on your brain. The brighter the screen the less the pupils of your eyes dilate, and reduce the ambient light that enters your eyes: probably why most people prefer to turn their brightness all the way up. Saccades move slower in a dim screen than on a bright screen. Because saccades move faster on a brighter screen[[https://www.ncbi.nlm.nih.gov/pubmed/29111439]], you are able to see more details.
+==== Blue Light Photons ====
-However, it is not advisable to use a very bright screen--be moderate. A very bright screen might cause headaches: though not to everyone.The light intensity might trigger migraines, especially for people with neurological deficits [[https://www.theraspecs.com/blog/computer-screens-headaches-migraines-and-concussions/]].
+Screens may look nicer when their brightness is up, but the high intensity of light is harmful for your eyes. ((https://pubs.rsc.org/en/content/articlelanding/2017/IB/c7ib00032d))\\
+https://www.chemistryworld.com/news/phone-screen-light-kills-human-eye-cells/3007113.article\\
+http://www.eyecarefun.com/bad-for-eyes-to-use-computer-in-dark
+Especially high frequency blue/violet light that carries more energy per photon. ((https://en.wikipedia.org/wiki/Visible_spectrum)).  Human eyes are designed to block UV light from reaching the retina.  Thus, the danger of creating reactive oxygen species (ROS) on the retina is highest from the blue light frequency range. ((https://www.allaboutvision.com/cvs/blue-light.htm))
-The goal is to let in as much light into your eyes as possible, to see the detail you need to see.  So while working at your monitor, the light comes in through both ambient and monitor sources.  If the monitor light is low, and ambient light relatively high, ambient light will burn your peripheral nerves, as eyes dilate to see the monitor (the low light intensity of the monitor causes your pupils to dilate). The effect is that the dilated pupils will allow more light to get into your eyes from the ambient light source. The best situation is low ambient light matching low screen brightness; if you increase the ambient temperature, you better increase screen brightness.
+In order to reduce retinal nerve damage, the goal is to let in as little light into your eyes as possible, where you can still see the detail you need to see.
-At low light, the pupils dilate and allows more light to enter the eyes. But that does not mean you will see more details. Saccades allow you to see more details, and they are very low at a low light intensity. Therefore, the best situation is to have a balance between the ambient light and the screen brightness.
+==== Reducing Concentrated Regions of Retinal Light Intensity ====
+The eyes can regulate the amount of incoming light through the [[https://en.wikipedia.org/wiki/Pupillary_light_reflex |pupillary light reflex]], where the pupil contracts or dilates according to the summation of light intensity onto both retina. ((https://www.quora.com/Does-peripheral-light-affect-the-pupillary-light-reflex-such-that-pupils-watching-TV-in-a-dark-room-will-be-slightly-wider-than-pupils-watching-TV-in-a-lit-room))
+Eyes evolved to have a relatively even intensity of light from the entire visual field, as obtained from sunlight's [[https://en.wikipedia.org/wiki/Atmospheric_optics |dispersion through the atmosphere]].
+While working at your monitor, light comes in through both ambient and monitor sources.  The summation of the light from the entire visual field contribute to how much your pupils contract.  The retinal nerve cells responsible for pupillary-light-reflex are the [[https://en.wikipedia.org/wiki/Intrinsically_photosensitive_retinal_ganglion_cells |Photosensitive Ganglion Cells]].
+If the light distribution reaching the retina is uneven, some cells may receive an unhealthy amount of radiation which can lead to cell death.  In the case of electronic displays, the distribution of retinal light intensity can be uneven if the ambient light and screen brightness are not balanced.
+For example, if you are watching a bright TV in a dark room.  As an extreme example, staring at the sun.  The opposite would be too dim of a display with intense ambient light, where peripheral nerves of the retina may be stressed.
+==== Improving Visual Acuity ====
+"As in a photographic lens, visual acuity is affected by the size of the pupil. Optical aberrations of the eye that decrease visual acuity are at a maximum when the pupil is largest (about 8 mm), which occurs in low-light conditions. When the pupil is small (1–2 mm), image sharpness may be limited by diffraction of light by the pupil (see diffraction limit). Between these extremes is the pupil diameter that is generally best for visual acuity in normal, healthy eyes; this tends to be around 3 or 4 mm." ((https://en.wikipedia.org/wiki/Visual_acuity))
+The best situation is where the monitor light and the ambient light have matching intensity.  But it's still not optimal if both sources are extremely bright.  A low ambient light and a matching low screen brightness, which still allows you to see the detail you need to see, is the best option for eye healh.
+In practice, with most computer monitors and most indoor lighting, you will be dialing the brightness level to zero.  Monitors are just too bright, unless sunlight is shining through your window in the background.  You can also play with the contrast to optimize image clarity and readability.
+If you practice this from an early age, you will find that most people in the era-of-screens have limited vision in low light.  Manufacturers are starting to take note, with now common features such as screens with automatic brightness, and a blue-light cycle that follows the [[health:circadian-rhythm|circadian rhythm]].
+==== Eye Strain (Asthenpia) ====
+The physiology of eye strain, or asthenopia, is not fully understood. ((https://scholar.google.com/scholar?q=related:9epKqfJgBQUJ:scholar.google.com/&scioq=cause+of+asthenopia&hl=en&as_sdt=0,33))
+Asthenopia has been categorized into eye surface and internal symptoms. ((https://www.tandfonline.com/doi/abs/10.1080/09500340600855460)) ((https://journals.lww.com/optvissci/Abstract/2003/11000/Is_all_Asthenopia_the_Same_.8.aspx))  Explanations for internal eye strain include muscular ache from [[https://en.wikipedia.org/wiki/Accommodation_%28eye%29 |accomodative]], [[https://en.wikipedia.org/wiki/Vergence |convergent]] and pupillary contractions.  External eye strain consists of "sensations of dryness and irritation on the front of the eye and caused by compromised conditions in the viewing environment."  ((https://www.tandfonline.com/doi/abs/10.1080/09500340600855460))

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