Post by thread:[EE]: Different backlight color on LCD?

Yes, it is possible, but the key is how the attachment of the lighting system is done and how the LED's are connected to the module. I would also think that it is not simple. Sometimes LED's are on a carrier PCB or on a flexible PCB. Often the same PCB is attached to the module glass via Conductive adhesive. If the LCD driver bonds took place in such a way you have to break them to get to the LED's then you will probably break the module and not be able to easily repair it. The LED's are piped into a plastic light pipe. This is often sandwiched between the flex and the PCB. So for LED's, if you can remove the PCB without destroying the bond to the glass, you can remove the LED's and replace with a different color. Remember that the voltage requirements for White and BLUE LED's are different than those for RED, Ambers, Green and Yellow (There are GaP, AlInGaP, and the White and Blue GaN's). You will likely also need to find a LED in a similar package to the original to make it work. Mechanical Tolerances are tight for Backlights. Finally the backlight light pipe may be tuned to the particular wavelength of light it was designed for, but this is less critical. For EL's it's a bit more tricky. If they are attached with conductive adhesive, then you probably will not easily be able to replace the EL. If they have solder tabs, then you have a better chance, but solder tabs are delicate and take care to work with - don't get your iron too hot during removal. Also going from EL's at > 150 Volts at 1000 to 250 hertz is not compatible with LED's a circuit change is again needed. If you go from a EL to a LED you also need a light pipe which is difficult to find that matches your particular display mechanics. In both cases if the light pipe or EL panel is adhesively attached to the glass, then you have to be careful on disassembly. This could damage the transfector -- the thin piece of paper which is between the light pipe and the rear polarizer for the display. This would make an uneven spot in the display. Finally if you get any dirt between the transflector and the backlight it will be visible. So you can do it, but I don't think it is easy and it depends on your particular display and its initial type of backlight. Steve Smith Electrical Engineer {Original Message removed}

On Mon, 7 Oct 2002, Pic Dude wrote: *>About to order a 24x2 or 40x2 LCD, but before I do.... *> *>For either LED or EL-type backlit LCD's, can I change the backlight *>color easily (to red)? No. *>Okay, forget "easily" -- can it be done w/o *>destroying the display? Sometimes. Older displays had the backlight a slab of plastic with chip leds molded in it and you could take it out and change it for another. Newer displays almost always have the backlight unit laminated to the back polariser to improve light transfer. Attempts to take those off lead to bad results. Peter -- http://www.piclist.com#nomail Going offline? Don't AutoReply us! email .....listservKILLspam@spam@mitvma.mit.edu with SET PICList DIGEST in the body

So what's wrong with using a red filter in front of the display? This has the advantage of giving the display additional protection against physical damage and a nice look when the display is off. KISS "Peter L. Peres" wrote: {Quote hidden}> > On Mon, 7 Oct 2002, Pic Dude wrote: > > *>About to order a 24x2 or 40x2 LCD, but before I do.... > *> > *>For either LED or EL-type backlit LCD's, can I change the backlight > *>color easily (to red)? > > No. > > *>Okay, forget "easily" -- can it be done w/o > *>destroying the display? > > Sometimes. Older displays had the backlight a slab of plastic with chip > leds molded in it and you could take it out and change it for another. > > Newer displays almost always have the backlight unit laminated to the back > polariser to improve light transfer. Attempts to take those off lead to > bad results. > > Peter > > -- > http://www.piclist.com#nomail Going offline? Don't AutoReply us! > email listservKILLspammitvma.mit.edu with SET PICList DIGEST in the body -- http://www.piclist.com#nomail Going offline? Don't AutoReply us! email .....listservKILLspam.....mitvma.mit.edu with SET PICList DIGEST in the body

I tried that with a small piece of light red acrylic (no backlight) and it was next to invisible. But now that I think about it, perhaps I could just keep the backlight on all the time. Will need to find one with a backlight and run a test... Robert Rolf scribbled: > > So what's wrong with using a red filter in front of the display? > This has the advantage of giving the display additional protection > against physical damage and a nice look when the display is off. > KISS > -- http://www.piclist.com#nomail Going offline? Don't AutoReply us! email EraseMElistservspam_OUTTakeThisOuTmitvma.mit.edu with SET PICList DIGEST in the body

At 01:03 PM 10/7/02 -0600, you wrote: >So what's wrong with using a red filter in front of the display? >This has the advantage of giving the display additional protection >against physical damage and a nice look when the display is off. LEDs are fairly monochromatic (compare the output curve in nm to the pass band of your filter in nm) so a red filter on a yellow or green backlight will not have results that are typically desirable. >KISS But not *too* simple (A. Einstein, I believe). Best regards, Spehro Pefhany --"it's the network..." "The Journey is the reward" speffspam_OUTinterlog.com Info for manufacturers: http://www.trexon.com Embedded software/hardware/analog Info for designers: http://www.speff.com -- http://www.piclist.com#nomail Going offline? Don't AutoReply us! email @spam@listservKILLspammitvma.mit.edu with SET PICList DIGEST in the body

On Mon, 7 Oct 2002, Robert Rolf wrote: *>So what's wrong with using a red filter in front of the display? *>This has the advantage of giving the display additional protection *>against physical damage and a nice look when the display is off. Nothing assuming you have white or at least orange backlight. Otherwise the backlight will be mostly dark and still green (there is NO red light in a green LED backlight. One look at an optical spectrum analyzer output will tell you all you need to know). Strangely some older green LEDs DO have weak red output in them, especially at low current. None of the new ones have it. (by old I mean 10+ years old). Peter -- http://www.piclist.com#nomail Going offline? Don't AutoReply us! email KILLspamlistservKILLspammitvma.mit.edu with SET PICList DIGEST in the body

Shouldn't be too hard. LCDs are often built to allow backlights to be inserted late on in the production process, and so they can often be easily removed. On Mon, 7 Oct 2002 13:10:47 -0400, you wrote: >About to order a 24x2 or 40x2 LCD, but before I do.... > >For either LED or EL-type backlit LCD's, can I change the backlight >color easily (to red)? Okay, forget "easily" -- can it be done w/o >destroying the display? > >Thanks, >-Neil. -- http://www.piclist.com hint: The list server can filter out subtopics (like ads or off topics) for you. See http://www.piclist.com/#topics