As many know, analogue LCD monitors are coming down in price and approaching the $200 mark. It is now becoming economical to purchase a 14 inch or 15 inch LCD monitor and use it for a projection panel.
Advantages are
Modern technology
Easy interface to computer
Good resolution
Better light transmission characteristics than older projection panels
Ready availability
Relatively cheap.
With these advantages compared to projection panels one would think traditional 10 - 15 year old projection panels would be abandoned in favour of modern LCD monitors.
Traditional high end projection panels just as Sharp QA 2500 on Ebay have been sold at $500. Vga panels such as Nview Spectra C are close to $200 on Ebay and some models do not have video in, only computer in. Freight to areas outside the USA can be very high so if you live in an area outside the USA there is not only the panel cost and depending on your currency conversion ratio to the US dollar that can be quite high, but freight costs can make the whole purchase too expensive.
Desk mounted LCD monitors seem to be the natural succesor to projection panels and could be in widespread use already except for one serious problem.
Most LCD monitors have a pc board up one side of the panel, and a pc board across the top of the panel. The two boards are joined together by a short length of (usually brown ) flex cable.
This flex cable has to be lengthened to allow the two pc boards to be moved out of the way to allow a powerful external back light source to project the image.
It is not an easy job to lengthen the flex cable.
On this forum, of four known attempts to do this two have succeded and two have failed. In the case of the failures, the panels have become inoperative and unusable.
So the success ratio is not very high and it is unlikely to become higher because each individual attempt is usually a solo effort.
It did occur to me that it may be unneccessary to lengthen the flex cable at all, and the monitor could be used with only minor modifications.
Many modern LCD monitors have side mounted backlight(s) which direct their light onto a piece of prepared glass or plastic which pipes the light across the panel and directs the light forward and hence provides an illuminated panel.
If the side mounted light could be replaced by a much stronger light it may be possible to create a usable projector.
Many folk are using 400 w Metal Halide. It is a relatively simple optics matter to collect a portion of that light and turn it into a replica of the original LCD panel backlight.
In addition, as is well known, conventional MH setups waste half their light output because LCD's only accept ploarized light of one particular polarization. This may be either the P polarizartion or the S polarization depending on panel details. The other polarization is simply wasted in heating the LCD first polarizer. This causes gradual clouding of the first polarizer and gradual dimming of the picture.
However many modern LCD monitors recycle the normally wasted 50 percent light by reflecting it several times from a very highly reflective mirror mounted behind the normal backlight assembly. The reflection causes a reversal of polarization and now the full output of the light is available rather than 50 percent.
It does need proven that replacing an LCD backlight with a much higher power unit would indeed result in a usable projector,
The advantages seem considerable and well worth further investigation.
Advantages are
Modern technology
Easy interface to computer
Good resolution
Better light transmission characteristics than older projection panels
Ready availability
Relatively cheap.
With these advantages compared to projection panels one would think traditional 10 - 15 year old projection panels would be abandoned in favour of modern LCD monitors.
Traditional high end projection panels just as Sharp QA 2500 on Ebay have been sold at $500. Vga panels such as Nview Spectra C are close to $200 on Ebay and some models do not have video in, only computer in. Freight to areas outside the USA can be very high so if you live in an area outside the USA there is not only the panel cost and depending on your currency conversion ratio to the US dollar that can be quite high, but freight costs can make the whole purchase too expensive.
Desk mounted LCD monitors seem to be the natural succesor to projection panels and could be in widespread use already except for one serious problem.
Most LCD monitors have a pc board up one side of the panel, and a pc board across the top of the panel. The two boards are joined together by a short length of (usually brown ) flex cable.
This flex cable has to be lengthened to allow the two pc boards to be moved out of the way to allow a powerful external back light source to project the image.
It is not an easy job to lengthen the flex cable.
On this forum, of four known attempts to do this two have succeded and two have failed. In the case of the failures, the panels have become inoperative and unusable.
So the success ratio is not very high and it is unlikely to become higher because each individual attempt is usually a solo effort.
It did occur to me that it may be unneccessary to lengthen the flex cable at all, and the monitor could be used with only minor modifications.
Many modern LCD monitors have side mounted backlight(s) which direct their light onto a piece of prepared glass or plastic which pipes the light across the panel and directs the light forward and hence provides an illuminated panel.
If the side mounted light could be replaced by a much stronger light it may be possible to create a usable projector.
Many folk are using 400 w Metal Halide. It is a relatively simple optics matter to collect a portion of that light and turn it into a replica of the original LCD panel backlight.
In addition, as is well known, conventional MH setups waste half their light output because LCD's only accept ploarized light of one particular polarization. This may be either the P polarizartion or the S polarization depending on panel details. The other polarization is simply wasted in heating the LCD first polarizer. This causes gradual clouding of the first polarizer and gradual dimming of the picture.
However many modern LCD monitors recycle the normally wasted 50 percent light by reflecting it several times from a very highly reflective mirror mounted behind the normal backlight assembly. The reflection causes a reversal of polarization and now the full output of the light is available rather than 50 percent.
It does need proven that replacing an LCD backlight with a much higher power unit would indeed result in a usable projector,
The advantages seem considerable and well worth further investigation.
Verbose Mustafa and I were thinking of replacing the CCFT with a line of high-output LED's... granted that the sum of the outputs of the LED's was greater than the single CCFT. I might try this with my small Sharp 5.7" panel when it comes in the mail, although I think it's truly backlit, and not side-lit. I think your idea definately has merit, and I would like to see it tried.
--Clint
--Clint
something new everyday 🙂
Good info! I'm interested to know if the theory could be emulated on a "non hi-tech" screen. I have a couple of "light pipe" panels from these junk LCD's I first got, behind them is a "super white" sheet of paper (sort of reflective). Curious what would happen if that were replaced with say "mylar" pulled tight to eliminate wrinkles.
zardoz
Good info! I'm interested to know if the theory could be emulated on a "non hi-tech" screen. I have a couple of "light pipe" panels from these junk LCD's I first got, behind them is a "super white" sheet of paper (sort of reflective). Curious what would happen if that were replaced with say "mylar" pulled tight to eliminate wrinkles.
zardoz
I'd say "go for it" Zardoz. 🙂 I don't know if you got any of those polarizing sheets in your junky LCD panels, but using those might help also to reflect back the light, switch polarization, and back through the screen or something. I just heard a little bit about that in the forums. 🙂 I'm not sure if any of what I just said is correct. 🙂 Good luck! Keep up the good work. 🙂
--Clint
--Clint
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