Re: Oil on my screen? (fwd)

Chris Immer (immer@Magnet.FSU.EDU)
Wed, 23 Apr 1997 12:57:08 -0400 (EDT)

What you are seeing here is not a defect of the OGO. It is a
fundamental principle of physics. What happens is that in order for
the touch sensitive screen to work, they have two pieces of
semiconducting plastic with a very thin layer of insulating fluid
between them. When the thickness of the layers get to be the same
order of magnitude of the light incident on the films this thin layer
of liquid between them causes light in interfere
constructively/destructively and you get an interference/diffraction
pattern. If you notice, the rings are milticolored, just like a
rainbow. This is the same principle that causes the light patterns in
a rainbow, a prism, and...a thin film of oil on water. This is why it
looks like there is "oil" in the OGO. The reason that you notice it
in the grocery store and not at home, or for that matter, the reason
you notice it under different lighting conditions is that different
light have different frequency spectrums. The light in grocery
stores are often halogen lamps, that have a VERY large spectrum
compared with normal incadescent lamps. Some of the wavelengths in
the halogen lamp must be the same order of magnitude as the thickness
between the films, and this wavelength is not present in the
incadescent lights. I have seen these rings most often with halogen
lights, but sometimes I can see them with fluorescent lights (which
also have a larger spectrum than incadescent).

Not to worry, there is no defect in you machine, it is a bueatiful
artifact of physics.

This effect is commonly given the name "Newton's rings". It's not
from the Apple Newton, although you see this effect on the Apple
Newton as well, it's named after the physicist Issac Newton.

Hope this helps.

> I have this problem as well, however, I did not notice it until
> one day in the grocery store which had high hanging fluorescent(sp?)
> lighting. That is just about the only place I can notice it. I think
> I saw it another time in a similar type lighting environment but can't
> remember where. After leaving the grocery store the 'oil' was
> impossible to see. I thought about sending it back but I figured the
> new one would do the same thing and other than the 'oil' everything was
> working perfect...I love my omnigo. From my experience I believe it to
> be a lighting thing. I suppose that it could be temperature related since
> it is colder in a grocery store, however, I have been in other cold places
> with my OG and not noticed it.
> Hmmm...I wonder if anyone has asked HP about this?
> Good Luck,
> Scott
> > Dear Frank,
> >
> > I have had the same problem for a long time. I also asked the list for
> > comments, but didn't receive any explanations other than to return it
> > while it was still under warrantee.
> >
> > However, I think the problem may be temperature-related. It doesn't seem
> > to be on the screen if the room temperature is above 70 degrees or so. In
> > the Bay Area many houses (eg. mine) do not use central heating unless it
> > gets below 60 or so. So I find that in the early morning and late night
> > that oil slick appears, but disappears during the warmer times of the day.
> >
> > It could also be light-related, but I don't think so.
> >
> > Peter
> >
> >
> > On Wed, 23 Apr 1997, Frank Koedood wrote:
> >
> > > Date: Wed, 23 Apr 1997 03:33:30 -0700
> > > From: Frank Koedood <>
> > > To:
> > > Subject: Oil on my screen?
> > >
> > >
> > > Hiya,
> > > I recently bought an Omnigo 100 and I must say I really like it,
> > > but something has been happening and I'm wondering... Sometimes an oil
> > > like splash develops underneath my screen. A bit like does early
> > > seventies light effects. It seems to be sensitive to the pen. I think
> > > it has to do with changes in temperature but I'm not sure. Can anyone
> > > help me? TIA.
> > >
> > > Peace,
> > >
> > > Frank.
> > >
> >


Chris Immer