Ah ha! Good old Newton's Rings.
This is very easy to explain.
Newton's Rings are formed by the constructive and destructive
interference of light rays as they pass through a medium that
refracts to various degrees.
On the Newton, the LCD glass has a plastic touch screen on top.
The touch screen is separated by a tiny amount from the glass.
When the screen is pressed, that part moves closer to the LCD
glass.
A ray of light can reflect off the bottom surface of the touch
screen or reflect of the top surface of the LCD glass.
Due to the fact that the ray travels a wee bit further to the
LCD then the touch screen, it will be slightly out of phase
with the touch screen reflected one.
Now for the magic...
If two signals are 180deg out of phase, they cancel.
If they are in phase, they add.
If they are anything in-between then they add or cancel a little bit
depending on their relative phase difference.
So, the upshot of all this is that you get dark patches where there
is cancellation, light patches where there is addition and Grey
patches in-between. (actually, the in-between will be colored but
lets keep things simple).
On certain peoples Newton's, the space between the touch screen and the LCD
will vary and can change with time/temperature/pressure/humidity so
these rings will manifest themselves from time to time.
Annoying but no harm, these rings cannot be washed away as they are not
a physical but a visual phenomenon.
And there are definitely no liquids involved here but the same kind
of phenomenon can be observed when oil and water mix.
PCBman
> If it's like my ump2000, it is caused by contact between the
> actual LCD
> glass and the protective writing surface that 'floats' above
> it. I'm not
> sure if there is some sort of fluid in between the two, but
> that's the look
> of it, oily and rainbowy (is that a word?).
>
> Cleaning my screen does nothing to counteract this, and the better the
> lighting in the room, the less noticeable the phenomenon...
>
> --
> Joe Anthenat ><>
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