Talk:Backlight

Bogus Test Procedure

"This can be tested by a user simply by waving a hand or object in front of the screen. If the object appears to have sharply-defined edges as it moves, the backlight is strobing on and off at a fairly low frequency. If the object appears blurry, the display either has a continuously-illuminated backlight or it is operating at a frequency that is too high for the brain to perceive."

No. Humans can perceive substantially faster flickering if each pulse falls on a different part of the retina. This is the principle behind POV displays, and I have used it to observe LEDs pulse width modulated at many hundred hertz. Furthermore, sharply defined edges indicate short on time, not low frequency. 207.119.52.172 (talk) 08:10, 8 June 2011 (UTC)

I have seizures as a result of certain frequencies of flicker, including the flicker produced by dimmed LEDs. You are definitely correct about being able to see substantially faster flickering, as I'm able to see flicker resulting from things like CFL bulbs--but this test procedure is correct in that you can typically determine whether an LED screen is at full brightness using this method. When I'm in doubt, I often use this technique to make sure I can look at a screen safely. As such, I wouldn't call it a "bogus test procedure," though maybe some rephrasing is needed to make it a bit more accurate. 76.176.202.233 (talk) 11:38, 31 December 2013 (UTC)

LED

I have a question about LED backlighting for LCDs, which I was very excited to hear about, since the color wavelengths could be more closely matched and presumably more efficient.

However, one of the ways I thought it might work is different than what is being done now, and I was wondering if there was any talk of doing this other way?

I had thought maybe the LCD would be MONOCRHOME, and that each color of LED would fire out of phase. So instead of 60 Hz, you'd have 180 Hz, with red, green and then blue LEDs each taking turns.

The advantage would be a high resolution picture and more efficient use of light energy.

So 1/180th of a second the mono LCD displays the image for the red color channel, and then all the red LEDs fire.

Then 1/180th of a second later, the LCD does the green image and the green LEDs fire, etc.

My friend suggested that this would not be fast enough, and that you would be a "rainbow effect", similar to the artifact caused by early color wheels in DLP sets.

I think that "rainbow effect" was fixed by varying the borders on the color wheel in DLP sets, and I wondered if a similar workaround of LED firing patterns could fix it in LCD/LED displays?

Of course another idea would be to run the whole thing at 360 Hz. So for each 1/60th of a second video frame, you'd get the sequence twice, r g b r g b. The only problem there, I realize, is the refresh rates of LCD panels. But I think they are getting close to 5 ms now.

So anyway, has anybody talked about this scheme, and is there a name for it?

Talk pages are for discussing the article. They are not forums for general discussion. 216.69.219.3 08:36, 15 October 2007 (UTC)

It is being considered as an alternative and might need inclusion in the article, however LCD update frequency is not good enough as of yet. It seems that Apple at least is using white LEDs in their labtops. --Thorseth (talk) 08:43, 6 August 2008 (UTC)

Laptop

What kind of backlight was usual for laptop computers of the 1990s, and what kind for modern cellphones? Jim.henderson (talk) 14:52, 15 April 2008 (UTC)

LED technology details needed

There are multiple LED technologies out now, the type of LED technology used needs to be clarified. OLED (organic LED) would be a waste of time, since they have limited lifetimes. Wikip rhyre (talk) 08:05, 5 September 2008 (UTC)

Problem with white LEDs?

The article correctly points out that most current white LEDs are deep blue with yellow phosphor. This is sufficient to fool the eye (for some people, not for me), but cannot be expected to yield a good color range when viewed through an LCD, no matter how the LCD colors might be adjusted. The article should discuss this important point, since it probably occurs to any intelligent person.

This issue may or may not be applicable to the most recent and more expensive white LEDs that have a better color distribution. I don't know. David (talk) 13:57, 3 March 2009 (UTC)

Incandescent backlights

Back in the early 1990's I was offered something called an "Allen Bradley Advisor" color LCD graphics display which used a couple of projector lamps to light the screen. The salesman stressed how easy it was to change the bulbs...every month. We didn't buy that one, holding off till we could afford CCFL backlighting just a little later. Also, I'm pretty sure my first LCD watch had a tiny grain-of-wheat bulb that sucked the battery down at an alarming rate. All personal experience and therefore original research, but surely there's a reference we can find? Restored the section, there's no deadline and today's generation should be exposed to the follies of the past so as not to repeat them. --Wtshymanski (talk) 15:44, 8 December 2014 (UTC)