LED backlight flicker

[majkel]

Hi!
I'm new to this forum, but a long time reader of AT. I wanted to ask my question here, because I really enjoy AT reviews and forum discussions, as it seems that editors as well as most of the forum users know what they write about (which unfortunately isn't the norm...), so I count on your experience

To the point (sort of): I recently bought a few monitors (both DELL: 24" IPS reviewed at AT and 22" touchscreen IPS, don't remember exact models but that's not the point) and a laptop. I've read few reviews before buying, including AT's review of the laptop (DELL XPS L502x), so I opted for the FullHD display there. I run a small software company, so we mostly stare at text all day and we wanted good displays as crappy ones that we've had were making our eyes bleed.

Everything about the new displays is a million times better than the old ones except for the backlight. Old ones where CCFL, these are LED.

As far as I know, dimming LED brightness is just about making in blink more and more so that it's on for shorter periods of time and off for longer which makes it appear darker. Similar concept is used in DLP projectors to expose the eyes to each color separately, but very quickly, so that eyes only see the combined color.

The problem is that if I focus on it, I can see the rainbow effect when looking at the DLP projected image. It's even easier to see when you move your eyeballs randomly for a while looking at it.

Similarly, I can see the backlight blinking in these monitors when they're below 80-90% brightness. It's not as annoying as 60Hz CRT, but it makes your eyes tire quicker. You can easily see the strobe effect when you wave your hand in front of the screen. The lower the brightness, the easier it is to see. I feel as disappointed as with fluorescent lightbulbs which were supposed to be great and turned out to blink and make colors look crappy.

The questions:
1. Am I the only human having this problem?
2. Are all LED backlit displays like this? I guess not, because a crappy (standard 14": 1366x768 dark, bad colors and viewing angles) display on a Lenovo Y470 laptop we have doesn't have this problem even at darkest setting.
3. Are all good/hi res/bright displays like this?
4. Why don't reviewers mention the blinking when reviewing monitos?
5. Why is high brightness considered a perk in reviews? Especially in a desktop monitor that never gets to be outside? I imagine that the brighter the display is, the more it blinks when dimmed and dimmed it must be if you don't want to wear sunglasses at night

 

[Phynaz]

Try this:

http://en.wikipedia.org/wiki/Backlight#Flicker_due_to_backlight_dimming

I wouldn't expect a modern display to exhibit flicker.

 

[majkel]

Thanks!
That answers the first question: I'm not the only one.
The rest remain even stronger - I also didn't expect a modern display to exhibit flicker, but apparently they do and noone mentions it in the reviews.

 

[Modelworks]

LED used for back lights pose a problem not easy to fix. There are two ways to control the brightness, PWM like in the wikipedia article and current control . Current control is just like it sounds, you lower the current going to the LED and it dims. LED used as back light are a problem when dimmed by lowering current because LED change color when the current flowing to them changes. Lower the current to an LED that is bright white at full current and it can look blue, which destroys the white balance of the colors displayed.

If a manufacturer is extremely careful they can mix and match LED so that dimming via current control doesn't change the white balance, but it takes someone who really knows what they are doing and that will figure into the cost of the display since a lot of testing is involved.

The ideal back light is actually incandescent lighting. It can be dimmed easily, exhibits easily manageable color changes but produces too much heat and uses more power.