LCD Backlight question

I was prompted by the "Dixons" thread to Google for LCD Backlights and found
a site that sells them for lap-tops. I was amazed to see that they are just
very thin tubes. http://www.lcdpart.com/index.html
Question: How is the light so evenly spread (without banding or hot-spots)
across the whole panel.
Secondly - do you think that manufacturers will eventually rationalise the
range of tubes (it should be in their interests) and make them replaceable?

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John

John Plant wrote:
I was prompted by the "Dixons" thread to Google for LCD Backlights and found
a site that sells them for lap-tops. I was amazed to see that they are just
very thin tubes. http://www.lcdpart.com/index.html
Question: How is the light so evenly spread (without banding or hot-spots)
across the whole panel.

Google
Light guides, that spread the light over the back of the display, then
reflect or refract it forward through the display.
It's quite complex to get right, with many compromises.



Secondly - do you think that manufacturers will eventually rationalise the
range of tubes (it should be in their interests) and make them replaceable?

They typically are replacable, but not easily so.
Making them more easily replacable may cost a bit more, especially if
user replacement of a 3mm dia fragile glass tube is determined to be too
dangerous.

Having done a simpe backlight repair once or twice to a couple of old
laptops, it is uually done using one or two thin fluorescent tubes
positioned at the side(s) of a sandwich usually made up of (from the front
of the viewable screen) a protective plastic front cover, the LCD screen
itself, a thin diffuser layer of plastic (think of a piece of tracing paper
in terms of appearance) then a piece of perspex or glass that has finely and
highly polished edges - this was about 5mm thick on the models I repaired,
and finally a very white sheet of plastic. There was also a protective
plastic covering at the very back.

The process uses the internal reflective properties of glass/clear plastic
in a similar way to how light is channelled down a fibre optic cable. In
simple terms, the light from the tube at one side of the perspex is
reflected millions of times inside, and any light that escapes is reflected
off the white backing sheet back into the perspex sheet. This process
removes most of the uneveness by effectively scattering the particles we see
as light. The result of this is then blurred by the diffuser sheet which
also serves to prevent what's under the LCD screen being clearly visible to
the user.

Some screens with less efficient light scattering properties can appear
darker or brighter in certain areas when viewed from certain angles. The
LCD part of the screen needs the backlight so that the user can see what's
being displayed. When a backlight dies, shining a flashlight from certain
angles at the front of the screen usually allows enough light to pass
through to the underlying reflective material to allow you to see whether
the LCD itself is working.

Repairing LCD backlights can be straightforward if the only problem is the
tube and as long as you're very respectful of the electrical properties of
the inverter circuit which can give a nasty shock even when the screen is
powered down due to capacitors remaining charged. Definitely not for
someone who doesn't know what they're doing. Unfortunately, LCD screen
problems are often down to a bad inverter, and these are often hard to
source. With the price of LCD technology tumbling at an alarming rate, it
probably isn't worth risking injury trying to repair them.

Nick

"John Plant" wrote in message
...
I was prompted by the "Dixons" thread to Google for LCD Backlights and
found
a site that sells them for lap-tops. I was amazed to see that they are
just
very thin tubes. http://www.lcdpart.com/index.html
Question: How is the light so evenly spread (without banding or hot-spots)
across the whole panel.
Secondly - do you think that manufacturers will eventually rationalise the
range of tubes (it should be in their interests) and make them
replaceable?


One would think that with the cost of some of this stuff now being so high,
that manufacturers would be only too willing to try and sort problems out.

However according to a friend of mine who works for a local company which
specialises in repairing this sort of technology, when it comes to technical
assistance, information and spares, they are apparently finding it an uphill
struggle, especially when compared to the old days of CRT equipment.

I suppose like almost everything else these days, manufacturers design
(hopefully) for several years of trouble free performance, before an item is
relegated to the local landfill and the customer replaces it with the newer
and better model.


--


--
John

On Sat, 28 Jan 2006 08:54:26 GMT, "John Plant" wrote:

I was prompted by the "Dixons" thread to Google for LCD Backlights and found
a site that sells them for lap-tops. I was amazed to see that they are just
very thin tubes. http://www.lcdpart.com/index.html
Question: How is the light so evenly spread (without banding or hot-spots)
across the whole panel.

Very clever optics - I took one apart recently and there ware about 8 layers of different sheets of
interesting optical plastic stuff - diffusers, diffraction grating type stuff, selectively
mirror-halftoned layer etc. The diffraction sheets are really cool to look through - you get double
images of everything...

"Mike Harrison" wrote in message
...
On Sat, 28 Jan 2006 08:54:26 GMT, "John Plant"
wrote:

I was prompted by the "Dixons" thread to Google for LCD Backlights
and found
a site that sells them for lap-tops. I was amazed to see that they
are just
very thin tubes. http://www.lcdpart.com/index.html
Question: How is the light so evenly spread (without banding or
hot-spots)
across the whole panel.

Very clever optics - I took one apart recently and there ware about 8
layers of different sheets of
interesting optical plastic stuff - diffusers, diffraction grating
type stuff, selectively
mirror-halftoned layer etc. The diffraction sheets are really cool to
look through - you get double
images of everything...

I would imagine that putting that lot together again would prove
extremely difficult if not impossible.
Regards Mike.

"Mike GW8IJT" wrote in message
...
"Mike Harrison" wrote in message
...
On Sat, 28 Jan 2006 08:54:26 GMT, "John Plant"
wrote:

I was prompted by the "Dixons" thread to Google for LCD Backlights
and found
a site that sells them for lap-tops. I was amazed to see that they
are just
very thin tubes. http://www.lcdpart.com/index.html
Question: How is the light so evenly spread (without banding or
hot-spots)
across the whole panel.

Very clever optics - I took one apart recently and there ware about 8
layers of different sheets of
interesting optical plastic stuff - diffusers, diffraction grating
type stuff, selectively
mirror-halftoned layer etc. The diffraction sheets are really cool to
look through - you get double
images of everything...

I would imagine that putting that lot together again would prove
extremely difficult if not impossible.
Regards Mike.


Thanks for all the interesting info.


John

Mike GW8IJT wrote:
"Mike Harrison" wrote in message
...
On Sat, 28 Jan 2006 08:54:26 GMT, "John Plant"
wrote:

I was prompted by the "Dixons" thread to Google for LCD Backlights
and found
a site that sells them for lap-tops. I was amazed to see that they
are just
very thin tubes. http://www.lcdpart.com/index.html
Question: How is the light so evenly spread (without banding or
hot-spots)
across the whole panel.

Very clever optics - I took one apart recently and there ware about 8
layers of different sheets of
interesting optical plastic stuff - diffusers, diffraction grating
type stuff, selectively
mirror-halftoned layer etc. The diffraction sheets are really cool to
look through - you get double
images of everything...

I would imagine that putting that lot together again would prove
extremely difficult if not impossible.

Of course not.
Tedious and fiddly, yes.