3 ms·

Staring directly at a light source strains the eyes more than watching reflected light.

mrob 8y ago
By what mechanism of action? It can't possibly be true in general: e.g. staring at the reflection of the sun in a mirror strains the eyes more than staring at a candle.
- bonzini 8y ago
  A reflection of the sun on a mirror is a reflection of a very strong light source through a perfectly reflective medium.. A book or an e-ink screen is still ultimately sunlight, but it has scattered (which is reflection too) while passing through the atmosphere many times before reaching what you are looking at.
  - Avamander 8y ago
    Could this be some unknown effect of polarized light vs. non-polarized?
  - enriquto 8y ago
    So it's a question of total light intensity, not of being reflected or "direct" (whatever that means).
    - hestipod 8y ago
      I don't think so myself because I don't have pain in full sunlight reading print or E-Ink which is much brighter "nits" than an LED backlight produces ....but even low settings on an LED backlit computer hurt. There is in my opinion a difference between looking into a light source and looking at things that are visible due to reflected light like E-Ink, paper, the objects around us even if I cannot quantify it with scientific explanation.
      - enriquto 8y ago
        This makes no sense to me. There is only one kind of light and it has just so many parameters: basically, the distribution of intensities along the spectrum. If reflected and emitted light have the same intensities there is no physical way to distinguish them.
        hestipod 8y ago
        Ok. Regardless of the intuition, staring into a light source feels different to everyone I have ever known that staring at normal objects reflecting light, like paper etc. Someone above claimed that reflected daylight was a lot more nits than a laptop could put out so I was going with the idea that this is true. I can look at paper in bright daylight with no eye strain. I cannot look at most LCDs even at low brightness without bad eye strain. It's not PWM in my case as I have ruled that out. Its much worse on LED displays. Fact remains that staring at backlit stuff gives people eye strain in ways printed or reflective never does and it seems logical that staring at the direct light source is a part of this. I know its not scientifically measuring nits/lumens etc but stare into even a low wattage (15w etc) light bulb for a few min and see how it leaves you feeling...seeing spots etc. Then stare at a newspaper or book or E-Reader under a 250w lightbulb or even brighter sunlight outside...and notice how you do NOT have that same problem. Even with a much brighter light source there is something different about how/how much actually enters your eye. I'd love an answer as this is a major life problem for me.
        enriquto 8y ago
        I think the difference may be in the contrast between the letters. A printed paper under the sun is very bright, but the black letters absorb most of the light and they are very dark and easy to tell apart. For a bright computer monitor, both the black and the white pixels are very bright, forcing the eye to strain itself to distinguish between two very bright intensities, which is difficult. Does it add up?
        hestipod 8y ago
- yomly 8y ago
  If I had to guess it is probably a few things. Firstly staring directly at a light source means that you are seeing most the rays directly. The only attenuation you will receive will be scattering from the medium - presumably air which will be low. Seeing it from a second surface adds more effects - the surface may have absorb some of the light. Any real surface is also not going to have perfect reflectivity (everything from scattering, internal diffraction and destructive interference could occur). In short there will be loads of secondary/tertiary effects causing attenuation. Someone also mentioned polarisation, I also wonder about interaction between reflective surfaces which could cause additional attenuation via interference but the physics of waves has never been a strong point. The other major factor is the physiology of the eye - we evolved from a world that didn't have abundant light sources and it's hard to know the effect of focusing on a source of light that differs from the ambient profile.

mrob 8y ago

By what mechanism of action? It can't possibly be true in general: e.g. staring at the reflection of the sun in a mirror strains the eyes more than staring at a candle.

bonzini 8y ago
A reflection of the sun on a mirror is a reflection of a very strong light source through a perfectly reflective medium.. A book or an e-ink screen is still ultimately sunlight, but it has scattered (which is reflection too) while passing through the atmosphere many times before reaching what you are looking at.
- Avamander 8y ago
  Could this be some unknown effect of polarized light vs. non-polarized?
- enriquto 8y ago
  So it's a question of total light intensity, not of being reflected or "direct" (whatever that means).
  - hestipod 8y ago
    I don't think so myself because I don't have pain in full sunlight reading print or E-Ink which is much brighter "nits" than an LED backlight produces ....but even low settings on an LED backlit computer hurt. There is in my opinion a difference between looking into a light source and looking at things that are visible due to reflected light like E-Ink, paper, the objects around us even if I cannot quantify it with scientific explanation.
    - enriquto 8y ago
      This makes no sense to me. There is only one kind of light and it has just so many parameters: basically, the distribution of intensities along the spectrum. If reflected and emitted light have the same intensities there is no physical way to distinguish them.
      - hestipod 8y ago
        Ok. Regardless of the intuition, staring into a light source feels different to everyone I have ever known that staring at normal objects reflecting light, like paper etc. Someone above claimed that reflected daylight was a lot more nits than a laptop could put out so I was going with the idea that this is true. I can look at paper in bright daylight with no eye strain. I cannot look at most LCDs even at low brightness without bad eye strain. It's not PWM in my case as I have ruled that out. Its much worse on LED displays. Fact remains that staring at backlit stuff gives people eye strain in ways printed or reflective never does and it seems logical that staring at the direct light source is a part of this. I know its not scientifically measuring nits/lumens etc but stare into even a low wattage (15w etc) light bulb for a few min and see how it leaves you feeling...seeing spots etc. Then stare at a newspaper or book or E-Reader under a 250w lightbulb or even brighter sunlight outside...and notice how you do NOT have that same problem. Even with a much brighter light source there is something different about how/how much actually enters your eye. I'd love an answer as this is a major life problem for me.
        enriquto 8y ago
        I think the difference may be in the contrast between the letters. A printed paper under the sun is very bright, but the black letters absorb most of the light and they are very dark and easy to tell apart. For a bright computer monitor, both the black and the white pixels are very bright, forcing the eye to strain itself to distinguish between two very bright intensities, which is difficult. Does it add up?
        hestipod 8y ago
yomly 8y ago
If I had to guess it is probably a few things. Firstly staring directly at a light source means that you are seeing most the rays directly. The only attenuation you will receive will be scattering from the medium - presumably air which will be low. Seeing it from a second surface adds more effects - the surface may have absorb some of the light. Any real surface is also not going to have perfect reflectivity (everything from scattering, internal diffraction and destructive interference could occur). In short there will be loads of secondary/tertiary effects causing attenuation. Someone also mentioned polarisation, I also wonder about interaction between reflective surfaces which could cause additional attenuation via interference but the physics of waves has never been a strong point. The other major factor is the physiology of the eye - we evolved from a world that didn't have abundant light sources and it's hard to know the effect of focusing on a source of light that differs from the ambient profile.