I meant, is it continuous, or is it flashing like CCFL?
I mean... Why does Hong Kong and its people think that UseNet is for selling their namebrand knockoff products? How many aliases does the original poster have and use for spamming UseNet? Only The Shadow knows... --
Here's the question. Oh no, I forgot what was the question after having to wade through a signature that comprises 78% of the lines in the post consisting of random fluff quotes, proselytizing linux, and pointing at a particular gov't agency in a worldwide publicized post.
I can't answer the question, but I can make a few suggestions. My guess is, it is "flashing". First of all, LEDs give a relatively consistent color output, if operated at a constant current. If you attempt to control their intensity, by changing the current flowing in them, the color shifts. And good color control is necessary to get a nice white balance from the backlight. The next alternative, is called PWM or pulse width modulation. A constant current is delivered to the LED, for a variable period of time. The modulation will be at a frequency above the ability of humans to perceive. For the LED and control circuit, it probably isn't that critical what the frequency is - in other words, it is easy for them to make it high enough so you won't see a flicker. You might ask, why would intensity adjustment be necessary at all ? Two reasons. 1) Modern monitors have dynamic contrast specifications. When you view a movie, the backlight is turned down on demand, frame by frame, to give the best contrast ratio. This allows 3000:1 contrast from LCD panels that have only 500:1 contrast from the panel itself. It allows the quotation of an exaggerated contrast spec. 2) LEDs age with time. A LED will lose 50% of intensity within the first two years of service. To compensate for the loss of intensity, a photodetector in the LCD monitor can detect the shift, and increase the pulse width period to compensate. The compensation can be applied during the entire life of the monitor. The backlight level may also be adjusted, according to ambient lighting conditions in the room. The old LCD monitors, with their CCFL illumination sources do much the same thing. CCFLs are modulated at two frequencies. 1) The inverter runs at 25KHz or so. It converts 12VDC to 700-1000 VAC to start the CCFL running. The CCFL tube runs at a high voltage. The reason the CCFL inverter runs at 25KHz, is so the noise from the inverter operation, will be above the range of human hearing. 2) For intensity control, the inverter is run in bursts, at about 200Hz. The exact frequency is selected, so you won't perceive a flicker. (It's that old PWM thing again ) This provides a wider range of light intensity settings, than simply varying the 12VDC fed into the inverter. And it also allows the CCFL to run with a consistent coloring (at least, until the tube wears out and the light turns brownish). So in some ways, they're equivalent technologies, with similar capabilities. The ability to provide dynamic contrast, the ability to compensate for loss of light output with age. And relative freedom to select operating frequencies which won't be perceived by humans (either visually or aurally). The LED provides an advantage on color gamut. It's unclear, whether in all cases, the LED monitor is really saving a lot of power. I haven't seen measurement numbers to back up such a statement. And the LED might last longer, because it isn't dependent on a dirt-cheap inverter for its operation. That potentially makes it a more reliable technology. The reliability, really depends on the manufacturing, and how many corners they cut while making the product. (Extended Gamut) http://www.xbitlabs.com/images/monitors/samsung-sm-xl24-xl30/p2s.png Paul
That depends on the context. If that were entirely true, they would be rich. I have been messing with spam for a long time here on UseNet. No telling what that stuff is supposed to mean. --
LEDs age with time. A LED will lose 50% of intensity Does this mean all LED monitors, though cheaper to make, require replacement every few years?
The LED continues to operate, so it is not a problem. There is a graph here, to show the relative loss in intensity of various light sources, for comparison. Every generation of LEDs, has different properties in this regard. http://www1.eere.energy.gov/buildings/ssl/depreciation.html I just looked at a recently introduced high power LED, and it lists "70% lumen maintenance (L70) at 50,000 hours of operation", and 50000 hours is a decent lifetime. Paul