Thinkpads Forum

It's only visible to the human eye at the very lowest brightness setting (at 60hz too, its not in power save 50 or 40hz)

but its visible to a digital camera live preview all the way up to full brightness where it manifests as a scan line.

Is this normal or should i seek to replace the screen under warranty?

Anyone else ever notice this?

Fwimbw, I can't detect it on mine at the lowest brightness setting, but certainly people vary on how sensitive they are and at what threshold such things are detectable or not.

Some people are more sensitive to refresh rates. Some people can use 60hz all day even on a CRT and be fine while other need at least 85hz (me for sure). LCDs don't refresh as a CRT does, no scanning lines from top to bottom 1 by 1. CRT uses phosphurs that light up and eventually fade again till the electron gun comes back to light them back up in effort to keep them in "on" state. LCD pixels are just ON or OFF.

There are some newer LCDs that offer 120Hz (Samsung) but at that rate it probably sucks lots more power and therefore not a good idea for laptops. That new shiny $2,500 55" X 1080P LCD is only 60hz also and you probably never noticed it there.

Then again i could be on crack and just didn't read your question clearly, it's 2am! (WTF am i doing up!!)

well, simply put it flickers at brightness 0. at 1 thru max its not as noticable or bothering.

My only theory is that brightness is controlled by the inverter scaling the a/c hz that the backlight CCFL runs on.

//i guess if the T62 has LED backlit screen ill have to get that fru.

It's worth noting that while LCDs don't have millions of microscopic phosphors arranged in a RGB matrix like a CRT, LCDs do have millions of microscopic transistors arranged in a RGB matrix instead and just like how phosphors bleed photons over time, transistors bleed electrons over time. Both display technologies require continuous refreshing of the entire display area via different means but the net effect is identical.

So basically LCDs do in fact refresh line-by-line just like CRTs. The displayed image on an LCD is not updated in a piecemeal fashion with just a few clumps of pixels here and there updated whenever the GPU feels like they should be.

That said, the CCFL backlight can very well cause a perceptible flicker, especially if the LCD is view with one's peripheral vision which is more sensitive to minute variations in light compared to direct vision.

blackomegax wrote:My only theory is that brightness is controlled by the inverter scaling the a/c hz that the backlight CCFL runs on.

Exactly. Typical frequency is above 200 Hz so it can not be noticable at all. Although considering how crappy LCD panels Lenovo currently use I wouldn't be surprised that there is very low frequency when the brightness is set to min. Still, I'd try to compare it with another unit because it might indicate that the lcd panel is defective.

Bigger LCD panels (> 20") might also exhibit a flicker effect when displaying a solid color (mostly grey color) but it has different reason, it is described in this document http://www.intersil.com/data/an/an1208.pdf