What type of backlight is this? - Page 1
Forum section: electronics / projects

author: Eth7an
author_rank: Contributor
timestamp: June 12, 2019, 01:17:52 pm
content: I pulled this out of a cheap old monitor. I originally thought it would be easy to use this backlight as a task light, as I am lighting my workshop with a 55" led backlight from an old TV, and its amazing. This backlight is almost certainly high voltage, as I can see the wires going to it are directly connected across the output of two HV transformers on the top side of the power supply. The backlight panel itself is a piece of thick plastic or glass with a grid pattern on one side. This is not connected with any wires, and just sits between the edges of the housing, which is where the wires go.If anyone knows what type of backlight this is, or more information on it, that would be awesome!

author: oPossum
author_rank: Super Contributor
timestamp: June 12, 2019, 01:36:47 pm
content: CCFL (Cold Cathode Fluorescent Lamp)If you remove the diffuser from the frame, there will be 4 CCFL tubes along the edges.

author: Zero999
author_rank: Super Contributor
timestamp: June 12, 2019, 02:22:01 pm
content: Yes, CCFL backlit displays tend to have better colour rendering, but use more power than LED backlit ones, although more modern LEDs are just as good.Efficiency wise, a CCFL is not as good a modern fluorescent lamp with a high efficiency electronic ballast.

author: Eth7an
author_rank: Contributor
timestamp: June 12, 2019, 03:10:44 pm
content: Oh, wow. Thanks a lot! What is the easiest way I can drive them? I have connected the power supply to it and it does nothing, presumably because it needs a power on signal. I guess I'm going to have to probe around and see what the power on does. Any ideas what voltage the signal to start up would be?

author: james_s
author_rank: Super Contributor
timestamp: June 12, 2019, 04:16:41 pm
content: It's probably a logic level signal. You can also buy generic CCFL inverters for a few dollars from China that work fine.Do be careful, the output can be 1kV or more, it's not likely to kill you but it hurts if you touch it and you can get an RF burn which is particularly painful. The tubes are also very thin and extremely fragile so handle them very carefully if you remove the from the frame.

author: lordvader88
author_rank: Frequent Contributor
timestamp: June 12, 2019, 10:12:43 pm
content: I thought it would be nice to try using 1 of these as a lamp in my room, but they're just a scrren, and pretty useless as much more than a reading light by your head maybe.They work ok modded as light boxes for documents and stuff. Other than, I'm not sure what different uses people get from them. I need a bigger lab.

author: lordvader88
author_rank: Frequent Contributor
timestamp: June 12, 2019, 10:18:22 pm
content: Quote from: james_s on June 12, 2019, 04:16:41 pmI just did that this winter. I took apart a TV, and then used it power board, and had to use logic high/low, I think 5V, to turn the light on/off.In my TV, it wasn't to hard to find Vcc for the lamps, and then trace out a few transistors and resistors, and maybe 1 opamp or comparator, or maybe that was a 6 pin resistor in my case.....but anyway it didn't take long to fin the control voltage, just using a DMM and pen/paper when unplugged

author: james_s
author_rank: Super Contributor
timestamp: June 13, 2019, 02:31:21 am
content: I've used the backlight from a broken LCD TV as an xray film viewer but that's not a very common need.

author: mikerj
author_rank: Super Contributor
timestamp: June 13, 2019, 09:07:24 am
content: The 6 way connector at the bottom of the PCB will provide power and control signals. There appears to be some kind of TV backlight connector standard; all the ones I have seen have two power pins (usually 12v) at one end of the connector, two ground pins at the other and the two pins in the middle will likely be a backlight enable and a brightness control.

author: tooki
author_rank: Super Contributor
timestamp: June 13, 2019, 02:33:36 pm
content: Quote from: Zero999 on June 12, 2019, 02:22:01 pmI don’t think that CCFL has been superior to LED backlights for a long time. And that’s not even considering LCDs with RGB LED backlighting, which allow for backlight spectra that closely match the filters on the subpixels.

author: Zero999
author_rank: Super Contributor
timestamp: June 13, 2019, 02:49:02 pm
content: Quote from: tooki on June 13, 2019, 02:33:36 pmHmm, I'm not convinced. I have an LED backlit monitor at home, I can't remember the brand, but it's around 3 years old and the colour rendering is poor, compared to lots of the older CCFL monitors I've used in the past. I do regret buying it and only did so because it seemed like a good price i.e. cheap. The problem is the red is very poor.

author: james_s
author_rank: Super Contributor
timestamp: June 13, 2019, 03:41:30 pm
content: You mentioned the reason right there, you bought a cheap monitor and the color rendering is poor. LED backlit monitors with excellent color rendering are widely available but they cost a bit more. I have one that has very good red, the old ccfl monitors look dull in comparison.The thing about ccfl is that once the phosphors got dialed in there was little savings in trying to cheap out on color rendering, they seem to be more consistent. They're pretty much a thing of the past though, I don't think anyone is still making ccfl lcds.

author: Zero999
author_rank: Super Contributor
timestamp: June 13, 2019, 06:59:20 pm
content: I've just checked the label. It's an Acer V226HQL. My advice is steer clear. It's crap.I still don't have the heart to throw it out. Perhaps I should donate it to a charity shop and get a better one?

author: wraper
author_rank: Unknown
timestamp: June 13, 2019, 07:07:56 pm
content: Quote from: Zero999 on June 13, 2019, 02:49:02 pmThat's because you bought monitor with bottom of the range WLED backlight. If you spent a bit more, you could get IPS, PLS or VA with decent WLED. If not cheaping out, you can get a LED backlit wide gamut monitor which is better than any with wide gamut CCFL, not to say standard CCFL.EDIT: actually you just made a stupid choice, at exactly the same price you could get a quite decent IPS monitor of the same size, not TN junk.

author: Zero999
author_rank: Super Contributor
timestamp: June 13, 2019, 07:36:05 pm
content: Quote from: wraper on June 13, 2019, 07:07:56 pmI accept I made bad decision, but could I have bought that back in 2016? If so, where?

author: wraper
author_rank: Unknown
timestamp: June 13, 2019, 08:02:32 pm
content: Quote from: Zero999 on June 13, 2019, 07:36:05 pmI bought a decent enough 24" IPS display for my father like 5 years ago for around EUR 120, smaller displays such as yours were of course cheaper. Your model is still sold and many good displays can be bought for the same price or even less.Also I have good understanding what is decent as I use wide gamut 30" LCD monitors with GB LED backlight. Previously had 30" with wide gamut CCFL.EDIT: it was AH-IPS PHILIPS 244E5QSD/00 bought in 2014 for EUR 125.98. Not even cheaper E-IPS.https://www.philips.ie/c-p/244E5QSD_00/lcd-monitor-with-smartimage-lite#see-all-benefits

author: tooki
author_rank: Super Contributor
timestamp: June 13, 2019, 09:16:44 pm
content: Quote from: Zero999 on June 13, 2019, 02:49:02 pmSo it’s just a super cheap display.Today’s best LED-backlit LCDs have better color rendition than any CCFL-backlit LCD ever had.

author: magic
author_rank: Super Contributor
timestamp: June 13, 2019, 10:15:15 pm
content: Quote from: wraper on June 13, 2019, 07:07:56 pmIf it really was a TN panel then all explanation you need is here and backlighting is a secondary concern