How to change the color of an LED?

[Jackie1]

An item I want to buy comes backlit blue and I need it to be GREEN. I contacted the seller and asked if I could change the bulb color with a green bulb condom and asked if it was currently a clear led, with a blue cover. THey said yes, but later they then wrote me back saying they made a mistake and the led inside doesn't have a cover, and an actual BLUE LED.

If I put a yellow bulb cover overtop the blue led, would it make it green?

https://www.ebay.com/itm/141731838162?ul_noapp=true

 

[berkeman]

Welcome to the PF.

It's not likely you can change the color of that display. White LEDs are more expensive than single-color LEDs, so it's unlikely they would use them in their display. Instead, just look for another display with the desired backlight color.

 

[Jackie1]

I've looked everywhere for weeks and there are none like this in green. THis is the size and color I want. It's just a single led that's lighting the screen. What can I just put a rubber yellow bulb condom over it, or remove and put in a green one?

 

[Jackie1]

EDIT, another pic added:

Ok, the seller was able to show me a picture of the board... The red circle are the leds. Crap, I wonder how hard to change to green led?

 

[trurle]

Seems like standard 3mm through-hole LED mount. You need to take the soldering iron, take out the blue LED and replace with green one, without any cap.

 

[Charles Link]

Note with an LED, there is a + lead and a minus lead. It will only light up if it is installed with the correct polarity.

 

[Jackie1]

Thank you. I've soldered before, a few times, and by no means an expert at all. What do you mean "without any cap?"

WHere would I buy green led's to fit this and wish I could send it to someone on here to help me if I can't do it.

 

[trurle]

Typically that through-hole LEDs can be found in some home centers (for example, Royal Home stock them). Or on Digikey.
Theoretically, i can fix it (have a large box filled with unused LEDs), but not sure the modification have any merit for you if you already do not have all necessary hardware - these thermometers are actually "cheap as dirt", and may be less money and time consuming to just buy the correct one.
Search something like
Pro LED DC 12V Digital Thermometer
on ebay.

 

[Jackie1]

Thanks. I actually saw that one, but it won't work as that one is C - celsius as most are, and i need the degress in F. This is being used in a car. Below are pics of the OLD SETUP.

This is the old unit above, Worked for 10 years. Ran off 1 AAA battery, and a friend helped out and found a resistor to make it work off 12v... It has a green backlight (hard to see in this day pic) and everything is green backlit in the vehicle, dash, radio, volts, etc, and wants to stick with green theme. I found the same silver unit again, as shown above and bought 3 of them for backups but they don't work correctly, as the outside looks the same, but the inside circuit boards changed and the green backlight turns off after 5 seconds not matter what I try inside, which is pointless at night...

SO, that's why I'm onto the new one I found, and I've looked for weeks for something that will fit in the hole I made out of the plastic veneer wood, but the blue will... I'm not that smart to figure out how to get the old one to work as there are a few new capacitors on the board of the older silver unit, again where the green light only stays on for 5 sec. Before, I soldered two leads together and the light would stay on all the time constant, but these updated ones I bought... I can't stop the light from tuning off after 5 sec... Again, this is why I wanted to try a new solution, and the new blue one will fit, but I just need it GREEN.

I appreciate all the replies and hope to get this working somehow. All I'm waiting for is the new blue led light, that's all I need as it's already a 12 v unit. Or I could ship it to you to inspect? Thanks again.

 

[Jackie1]

That's cool of you and thanks for helping out! THe one I found is in Kentucky. Meaning I can have it to me in 3-4 days. I'll have it ship to me first to make sure again it fits in that window, but it should...

 

[DaveC426913]

A little late, but I don't think just putting something yellow over / in front of a blue LED will work.
LEDs have a pretty narrow spectrum.

Filtering it through yellow will get you pretty close to ... black.

 

[Jackie1]

Thanks. Wish it was as easy as adding a filter :)

Just wanted to update. I got the unit and it fits in the old location that I posted above in the vehicle :) It fits perfect which in kinda unreal since that hole was custom sized with a file by me 10 years ago, got lucky I guess...

Now just got to figure out how to get it green led. Maybe someone knows what leds to buy or would anyone want to help me out with this project? I'm in PA.

It was mentioned above that from the circuit board it might be a 3mm hole through led. Are these it?

 

[trurle]

It was mentioned above that from the circuit board it might be a 3mm hole through led. Are these it?

Yes, on photo is most common LED with 3mm lens.

 

[Jackie1]

Ok. So. Confused again. As shown abovein my earlier post, the manufacturer sent pics of the circuit board before I ordered this and circled the leds supposedly on this board in red, see above posts. I just took the unit apart and I don’t see any leds on the board? I powered it up and they look like they are part of the lcd display and are embedded in the lcd? Am I right? Confused here. Below is pic of board and lcd I twisted off to the side.

 

[trurle]

View attachment 233978 Ok. So. Confused again as shown in my earlier post, the manufacture sent pics of the circuit board before I ordered this and circled the leds supposedly on this board. I just took the unreal apart and I don’t see any leds on the board. They look like they are part of the lcd display and are embedded in the lcd? Am I right? Confused here.

I see. This is the "LED backlight module" intended to reduce light losses of LED. It can still work with discrete LED, although with complications. You need to:
1) Cut the existing LED clear from diffusor plate using knife or heavy-duty nail cutter.
2) Either use "right angle" packaged LED, or bend leads of your LED to look sideways into diffusor panel
3) Connect LED lens and diffusor plate with a drop of transparent acrylic or silicone adhesive (recommended)

 

[Tom.G]

1) Cut the existing LED clear from diffusor plate using knife or heavy-duty nail cutter.

NO! Do not use a nail cutter.[/color] The hard plastic of the diffuser will crack. Use a hobby knife such as an X-Acto, or similar. Using the tip of the blade, make shallow cut strokes on the surface until you get thru the hard plastic. Carefully, like you are doing surgery on your finger.

Cheers,
Tom

 

[trurle]

NO! Do not use a nail cutter. The hard plastic of the diffuser will crack. Use a hobby knife such as an X-Acto, or similar. Using the tip of the blade, make shallow cut strokes on the surface until you get thru the hard plastic. Carefully, like you are doing surgery on your finger.
Cheers,
Tom

Well, you may have tried to cut used diffuser. I suspect some embrittlement by light happens. New one is more easy to handle, i had in one case even drilled 4mm mounting holes in diffuser. Although about knife you correct - my preferred tool for cutting materials like diffusers or rigid PVC is 30-degree cutter similar to X-Acto.

 

[Jackie1]

I see. This is the "LED backlight module" intended to reduce light losses of LED. It can still work with discrete LED, although with complications. You need to:
1) Cut the existing LED clear from diffusor plate using knife or heavy-duty nail cutter.
2) Either use "right angle" packaged LED, or bend leads of your LED to look sideways into diffusor panel
3) Connect LED lens and diffusor plate with a drop of transparent acrylic or silicone adhesive (recommended)

@Turle and others. THANK YOU... So, what the heck did the manufacturer send me above? They said this was where the led's were:

Is that for a backup led? Could I disconnect those side leds and put one led in the red circle? Lol. Why on Earth did they say that's where the leds go? And Tthere are two total leds in this, one at end end of the lcd glass...

I'd like to try this myself but I'll probably destroy it. As my father would say "Custom items just cause problems" LOL, well, the original unit lasted 10 years with a resistor to converted to 12v so that was a good run. As mentioned I can still buy the original unit but the circuitry changed and not sure how to get that orignal backlight to stay lit but someone here could prob figure it out (the silver unit that I had originally)

Crap.

Also, a search revealed this... Same idea?

https://www.instructables.com/id/DIY-LCD-backlight/

 

[Jackie1]

Another update. I wrote the company again and they tell me the factory led is: 0603 LED light

Is that wrong again?

 

[gneill]

Perhaps you could just change the whole backlight module? These guys appear to provide customized modules:

https://www.alibaba.com/product-det...m=a2700.7724857.normalList.126.5b6b2c99PMJBVL

 

[Jackie1]

Perhaps you could just change the whole backlight module? These guys appear to provide customized modules:

https://www.alibaba.com/product-det...m=a2700.7724857.normalList.126.5b6b2c99PMJBVL

Wow, that's pretty cool also. Had no idea that was even offered... I'll check that out as well.. So, the image that's displayed/projected on my screen now for the temp is programmed by the circuit board I guess in my current unit?

 

[gneill]

Wow, that's pretty cool also. Had no idea that was even offered... I'll check that out as well.. So, the image that's displayed/projected on my screen now for the temp is programmed by the circuit board I guess in my current unit?

That would be my understanding, yes.

The question is, how are the LCD and current backlight module bonded? Are they bonded, or does the module simply fit behind the LCD panel?

 

[trurle]

@Turle and others. THANK YOU... So, what the heck did the manufacturer send me above? They said this was where the led's were:

View attachment 233999

Is that for a backup led? Could I disconnect those side leds and put one led in the red circle? Lol. Why on Earth did they say that's where the leds go? And Tthere are two total leds in this, one at end end of the lcd glass...

From engineering standpoint, likely maker at first used stand-alone LED. Afterwards, they moved to SMT LED integral to diffuser, and interfaced it to the existing PCBs layout, either to consume stock of old PCBs or to save on PCB development.
Actually LED position is not that important - some light will go to diffuser anyway, regardless of location. Brightness may suffer though.

Also, a search revealed this... Same idea?
https://www.instructables.com/id/DIY-LCD-backlight/

Yes, very similar to what i do, down to the shape of diodes (i used stock of 2x4mm rectangular LEDs in previous projects). The only difference may be is what i prefer to use cuttings of diffuser plate scavenged from defective PC monitor instead of generic plastic plate - for better illumination uniformity and therefore reduction of number of LEDs. The 4-LED assembly in tutorial is a bit cumbersome, i.m.h.o.

 

[Jackie1]

Very interesting again! So I'm not crazy, it seems that board can be used a few ways.

Ok, now I saw this! Exactly what I want... BUT! Looks like this is only C, when I need it to display in F, and it shows 5v, where the blue one on ebay shows 5-25v. I'm using for 12v. Argh, don't think it will work? but this is what I want it to look like 100%

https://www.overclockers.co.uk/xspc-lcd-temperature-display-green-v3-flat-sensor-wc-206-xs.html

 

[trurle]

Very interesting again! So I'm not crazy, it seems that board can be used a few ways.

Ok, now I saw this! Exactly what I want... BUT! Looks like this is only C, when I need it to display in F, and it shows 5v, where the blue one on ebay shows 5-25v. I'm using for 12v. Argh, don't think it will work? but this is what I want it to look like 100%

View attachment 234036

https://www.overclockers.co.uk/xspc-lcd-temperature-display-green-v3-flat-sensor-wc-206-xs.html

Regarding temperature units (C or F), not much can be done without reprogramming firmware, which is not really feasible unless you are maker of thermometer. Regarding voltage range, most LCD units (as opposed to LED 7-segment) have stable enough supply current so you can adjust input voltage using ballast resistor or 2-3 LEDs in series in power supply line.

 

[Jackie1]

Perhaps you could just change the whole backlight module? These guys appear to provide customized modules:

https://www.alibaba.com/product-det...m=a2700.7724857.normalList.126.5b6b2c99PMJBVL

Well, I contacted them, and they want min order of $100 and no guarantee it will work or fit. So, so much for me trying to do this myself. I'm not giving up and one of the members on here will let me send it to him and he can make it work, but he's not in USA and it will take a while.

 

[trainman2001]

If you need to buy a good selection of LEDs for little $$$, try LEDswitch.com. They have many sizes, many colors. LEDs are temp sensitive so be careful when soldering to not stay on the junction too long. They are also easy to damage if you attempt to bend the leads too near the plastic body. Arrow Electronics sells some very tiny surface mount LEDs. They are very bright, and cost less than 30 cents a piece. Again… watch you soldering temp and how long you're on the joint. I'm a model railroader and use LEDs exclusively for scenic and building lighting. They're perfect for the application: little power consumption, little or no heat, don't burn out (in my lifetime) and I don't have to worry about opening up structures to replace them. I used to use current limiting resistors (max current 20ma), but now use LED driver chips where any applied voltage from 5 VDC to 90 VDC puts out 20ma. Only limiting factor in how many you LEDs you can string together in series is the voltage drop across each LED and the supply voltage. Example: 12 VDC source gives a series string of 4, 3 volt LEDs. If you need to run more from the source, since, depending on the source, you've only consumed about 80 ma, is to run series parallel configurations with a separate driver on each leg. The driver chips are $0.29 each, again, very inexpensive.

 

[davenn]

The question is, how are the LCD and current backlight module bonded? Are they bonded, or does the module simply fit behind the LCD panel?

they are generally just a strip of individual LEDs non-bonded, just held in place with the panel casing ...
I pull dozens of these apart to get the LED strips for other projects

here's 2 different strips from two different sized LCD panels I pulled apart

Dave

 

[sophiecentaur]

A little late, but I don't think just putting something yellow over / in front of a blue LED will work.
LEDs have a pretty narrow spectrum.

Filtering it through yellow will get you pretty close to ... black.

For anyone whether needs a particular practical solution or who just likes to 'know' stuff, I recommend a miniature spectroscope (sold for gemnologists mainly I believe). They're about the size of an AA battery so they fit a vest pocket easily. I bought one for about £30 and I have had hours of fun looking at various different light sources. Of course, it's only a qualitative thing and actually measuring levels could be a bit of a problem but I have been able to compare the spectra of tungsten, CFL and various LED sources. The LEDs used in domestic lighting are surprisingly wide band and it just may be worth while trying a simple filter if the source is 'blueish" white and fairly modern. I believe domestic lamps use a UV source with a range of phosphors to produce the nice filament-like spectrum.
Edit: The OP should EXPERIMENT with various coloured materials - like the green glass of a red wine bottle, for instance. The experimental filter doesn't need to fit over the display- just view through the bottle glass and then order a cinemoid stage lighting filter gel if it works. Only use a soldering iron if really necessary.

 

[Edelmere]

Green LEDs are the least efficient of all the visible LEDs. If you need really bright green LEDs it is probably better to use a green phosphor on a Blue LED similar to the way that white LED's are made.