View Full Version : LCD uneven brightness?

Jon P. Inghram
8th February 2007, 23:39
I'm having a problem (I think) with uneven backlighting or something like that with my new LCD. A couple days ago I bought an LG L1732TQ 17" and noticed that, especially with darker colors, the brightness fades darker towards the top of the screen. I figured it was a bad LCD so I returned it and got a "better" LCD, a 19" Samsung 931BF. However, it too becomes darker towards the top of the screen. I'm not sure if it's just a LCD disadvantage or if I've just got really bad luck. Here's three photos taken with the same exposure showing the effect with a dark background (RGB value of 53) viewed from above, directly in front, and below the screen.

8th February 2007, 23:57
Sadly I've seen that with a lot of LCDs over the years. In most cases it just seemed to come down to how well the screen was sealed or how flush it was with the mounting. If there's not a good seal you get leak through of the backlight.

I'm sure there's a better explanation of it, but it's actually a rather common occurrence.

Jon P. Inghram
9th February 2007, 00:05
Hmm... I'm finding it annoying enough that I may just return it (thankfully there's no restocking fee at Best Buy on monitors) and just put up with my old 17" Samsung CRT until SED, OLED, or some other technology replaces LCDs.

9th February 2007, 00:08
Yeah, it's a very common issue. You have to do some research before buying any model of LCD. Even within the same brand there can be a big difference in overall quality.

Jon P. Inghram
9th February 2007, 00:53
Yeah, it's a very common issue. You have to do some research before buying any model of LCD. Even within the same brand there can be a big difference in overall quality.

Unfortunately, I did do research and didn't see anyone complain about this. And just hooked up my CRT and it really looks icky running along side the LCD.

9th February 2007, 01:07
Have you looked at any of the Dell LCDs by chance? Not sure what sort of use you're after, but I've had two so far and they've been great (latest is a refurb at that).

9th February 2007, 01:22
I've noticed that in a lot of LCDs too Jon, but then once you have images on screen you don't ever notice it with the very odd exception. That case does look a little worse than normal though - (for the directly in front pic) - might be a case of bad luck. Neither of the samsungs in my home are quite that bad.

Jon P. Inghram
9th February 2007, 01:52
It was pretty annoying on websites with darker background graphics, and when looking at photos. I tried to ignore it but near the top there was a noticeable amount of dark image detail lost that would magically reappear when moved near the bottom of the screen.

I'm going to email Samsung and see if they'll just exchange it for a good one.

As for what it's used for... pretty much everything: internet, games, and non-professional photography. Hadn't looked at any Dell stuff, not sure where in town I'd even find any.

9th February 2007, 01:58
Yeah, if it is that noticeable there is a good chance it is not normal.

Just tried a bunch of different grey levels on my LG and Samsung, my samsung was pretty much perfect viewing straight on, and the LG just has a little bit of darkness in the top right corner extending about an inch.

9th February 2007, 03:39
To me, this does not look like ordinary backlighting unevenness - I'll post a pic later of my laptop's screen that shows that.

I think this is a problem with cheaper/faster LCD TN panels' viewing angles, as evidenced by the fact that it gets worse when you view from below. The further below it you get, the angle gets more acute. The angle towards the bottom of the panel is more obtuse than the angle towards the top if your eyes are positioned below the middle of the panel, so the problem gets worse for the top (because the viewing angle there is even worse - more acute - than from your eyes to the bottom).

TN panels often have very bad vertical viewing angles, and most of them are a lot worse if viewed from below, because most people view their monitors from above (that's also what ergonomics norms advise: Sit so that your eyes are aligned with the top of your screen - this will get you a 0° deviation from the perpendicular, while when you look at the bottom edge of the screen in this position, you'll view from ~30° above the perpendicular. There will be no point of the screen you'll view from below, in theory, and if you sit upright all the time.).

This is no defect; it's normal for cheaper screens and for most screens with fast response times, because they use TN panels. Get a screen with an IPS, S-IPS, MVA or PVA panel and you shouldn't have that problem anymore (or at least much less obvious).

9th February 2007, 08:16
Looks like thats a side-lit lcd module where they only use bulbs on one side instead of two. So, the light diffuser isn't designed very well since it isn't pulling enough light to the far end of the display. Usually you see that on laptops where the ccfl is at the bottom/hinge area of the display. Most desktop displays traiditonally use bulbs on two sides to light the display. You might be able to tell what kind of backlight array they use if you can look through the back and see any bright spots from the bulbs, or pop it open and look if the inverter connects to bulbs on both sides or just one side of the display.

Oh and yes and AZ mentioned, if you have a TN display then you're going to see quite a bit of color inversion at low levels at even small off center viewing angles.

Jon P. Inghram
9th February 2007, 12:58
Going to return the 931BF and get a 971P, which is a S-PVA screen that comes with a much nicer stand, full 8 bit color, and it can rotate to portrait mode too.

9th February 2007, 15:07
Hmm...I honestly haven't ever seen LCDs that wouldn't show this behaviour...but everybody here buys cheapest they can get for size and response time (stated by manufacturer) and cheapest laptops.

9th February 2007, 19:08
I've stuck with 8ms for my last two LCDs (17") - never see any ghosting so I won't bother going any faster.

Does anyone know if slow response time is more apparent on larger panels?

9th February 2007, 20:03
Generally speaking a larger lcd module will have slower response due to capacitance in the cells. Bigger panel = longer driver lines = slower response without using some overdriving and look ahead framebuffering techniques. Its pretty much gotten to the point however where a 17" and 21" panel have about the same response.

Jon P. Inghram
11th February 2007, 12:04
I've stuck with 8ms for my last two LCDs (17") - never see any ghosting so I won't bother going any faster.

Does anyone know if slow response time is more apparent on larger panels?

After playing with that 971P for a couple days, I've given up on LCDs entirely and am just going to go get a 19" ViewSonic CRT. The ghosting wasn't noticeable when looking at black text on a white background, but when I fired up Orbiter (http://orbit.medphys.ucl.ac.uk/orbit.html) the stars disappeared whenever there was movement, and darker textures in HL2 blurred into mud when moving. When watching a DVD like The Matrix the RTC artifacts looked like crap, turning smooth graduations of light into icky 4 bit looking bands and ghosts when moving.

11th February 2007, 16:27
Looked up a review on that 971P, it does suffer major ghosting. http://neoseeker.com/resourcelink.html?rlid=143537

Seems like you just have bad luck with buying LCDs :(

Jon P. Inghram
11th February 2007, 22:15
And worse luck finding reviews. :) The reviews I found didn't indicate it had partictuarlly bad ghosting.

13th February 2007, 11:39
Classic case of not looking at reviews then reading user comments.

Too the orginal problem sounded like poor viewing angles. I won't go back to CRT's now as they tend to suffer from annoying geomentry problems that used to send me crazy with frustration.