On Tue, Apr 3, 2018 at 1:02 PM, Alistair Grant <akgrant0710 at gmail.com>
wrote:

> Hi Eliot,
>
> On 3 April 2018 at 15:20, Eliot Miranda <eliot.miranda at gmail.com> wrote:
> > Hi Dark Themers,
> >
> >     in an earlier life I worked in optics, designing holographic cameras
> for
> > bubble chamber physics, so I know a little about focussing systems and
> depth
> > of field.  The iris in the eye expands or contracts to allow or restrict
> the
> > amount of light entering the eye, attempting to maintain a constant
> > luminosity on the retina so that either not too little, or not too much
> > light falls on the cones and rods in the retina.  When the iris is
> dilated
> > (open) the eye allows as much light as possible into it.  You can
> visualize
> > the light from a point (say a pixel) that reaches the iris as a cone.
> The
> > lens in the eye focuses this expanding cone back into a contracting one
> that
> > comes to a point on the retina corresponding to the position of the pixel
> > "out there on the screen".
> >
> > Focusing is achieved by a muscle around the eye's flexible lens, the
> cillary
> > muscle, which squeezes the lens into a more spherical shape to cause rays
> > entering the eye to bend more, brings no objects closer to the eye into
> > focus, or by the cillary muscle relaxing, allowing the lens to stretch
> back
> > to a flatter shape, to bend rays less, bringing objects further away into
> > focus.  In old age shortsightedness is caused by the lens loosing its
> > elasticity and remaining squeezed, and longsightedness by it losing
> > flexibility and the cillary muscle losing strength so that the lens
> cannot
> > be squeezed as much.  By the time we hit our 40's many of us will suffer
> one
> > of these two extremes and have to wear glasses either for reading or for
> > driving or, in my case, for both.
> >
> >
> > Getting back to the cone of rays from a pixel that the iris and lens
> > conspire to bring to a point on the retina, if there is a lot of light
> > incident on the eye and the iris is undilated then this cone is much
> > slimmer.  The result of these differing cones on focus is called depth of
> > field.  When the cone is "fat" depth of field is reduced; only pixels in
> the
> > same plane (actually a spherical surface, not a plane, because the
> retina is
> > spherical; film cameras have planar light receptors; the eye and camera
> > obscures etc have spherical light receptors) will be in focus; others
> out of
> > the plane will produce a diffuse circle on the retina.  When the cone is
> > "slim" (because more light is incident on the eye) depth of field is
> > increased because the size of the out of focus diffuse circle is smaller.
> > Consequently, when there is less light falling on the eye, depth of
> field is
> > reduced; the cones are fatter and as the eye roams the cillary muscle
> must
> > work to alter the curvature of the lens to keep things in focus.
> >
> > The implication for the dark theme is that, while it appears to have
> better
> > contrast (it does not; but more on that below), the real effect is that
> it
> > causes the eye to do more work than a light theme because the amount of
> > light entering the eye is less.  So both in the short term and especially
> > over the long term the dark theme, relative to the light theme, will tire
> > your collate muscle and cause your lens to stiffen or squish sooner.
> >
> > Why then, if what I'm saying is true, did all those World War Two
> military
> > aircraft use white letters on a black background?  My lotus europa is the
> > same.  The disc of the instrument is illuminated by a lamp so one can
> see it
> > at night, and were the panel painted white then, for the same contrast,
> much
> > more light would hit the eye that for white letters on a black background
> > and the pilot's (or driver's) night vision would be impaired as the iris
> > would contract.
> >
> > I don't want to fear monger, but I do want to suggest that it is
> healthier
> > and less wearing on the eyes to use light themes.
>
> Great description, thanks!  I went through this 2 or 3 years ago - I
> used to like dark themes because they looked "nicer".  Now I'm
> exhausted after looking at them for a few minutes.  I also get to
> enjoy dealing with multi-focal glasses.
>
> Although I do miss my green-on-black terminal...
>

Ha!!



> > Eliot
> > _,,,^..^,,,_ (phone)
>
> How can you type all this on a phone?  I'd be cross-eyed, as well as
> feeling like my phone had a dark theme (which it doesn't). :-)
>

Because I was snuggled up in bed having woken up early :-)


> Cheers.
> Alistair
>

_,,,^..^,,,_
best, Eliot
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