From: Robin Myers <email@hidden>
Date: Sat, 16 Jun 2007 17:55:30 -0700
To: <email@hidden>
Subject: Re: question on LED-backlit displays
On Jun 16, 2007, at 17:22 , Marco Ugolini wrote:
In a message dated 6/16/07 3:36 PM, Steve Upton wrote:
At 11:18 PM -0700 6/15/07, Marco Ugolini wrote:
The way I understand it, LED backlighting allows for control over
the actual
color temperature of the light source itself, whereas the current
crop of
LCDs uses a fluorescent backlight whose color temperature cannot
be altered.
this is only if the LED backlighting is supplied using a
combination of red,
green, blue (and perhaps other) LEDs
So, there is a possibility that the LEDs are single-source, not
triplets of
R, G and B light sources?
Marco Ugolini
Most high-brightness LEDs used for backlighting are "white" LEDs. The
actual LED chip is a blue LED coated with a blue light excited yellow
emitting phosphor. The phosphor allows some of the blue light to pass
through so the result is blue plus yellow light, thus "white".
Although single LED devices containing red, green and blue individual
dies have been around for many years, they are not as bright as the
white LEDs, so they are not usually used for backlights. High
brightness LEDs are needed because the LCD they are backlighting
greatly cuts the backlight intensity down before it gets out for us
to view.
Backlights using individual high brightness red, green and blue LEDs
are possible, but they present a very challenging task to the optical
designer to get the light to mix evenly in the narrow confines of a
display.
One technology that shows great promise for high brightness LED
displays is Organic Light Emitting Diode displays, known as OLED
displays. These are LEDs that can be created in large area patterns
on glass and plastic substrates making large self-luminous displays.
The main drawback to this technology is the lower lifetime of blue
OLEDs, about 5000 hours right now. This would be about 2 years of
24/7 operation. Most people think that a 10000 hour lifetime is
necessary for a viable full color OLED display. There are many
companies working on this technology so we should be seeing some OLED
displays in the near future.
Robin Myers