The properties of LED backlighting discussion
Posted: Fri May 14, 2010 4:18 pm
White LEDs are blue LEDs in sheep's clothing. Specifically, they are BLUE LEDs with a phosphor coat to convert the blue spectrum of light they emit into white light. They emit light in specific wavelengths.
LED life ratings are measured as "lifetime until 50% brightness" in the industry. When a LED is said to have a 50,000 hour life, this is when the LED is run in an environment where it is at 25C ("Room temperature") with proper manufacturing and binning. It will be run at its specified forward voltage and current, being adequately cooled. At 50,000 hours, it will reach 50% output.
LEDs that are overdriven (! Voltage and current too high) and/or often inadequately cooled have much shorter lifespans to 50% or even death! This can be low as a THOUSAND (1,000) HOURS!
However, LEDs run at lower than full power and adequately cooled can often exceed their expected lifetime specs. LEDs do not have a "million hours" of practical life. Numbers such as "100,000 hours" are very lax estimates of what they practically are at full power. Realistic numbers closer to the lower tens of thousands will be what you can expect from a LED until 50% loss of brightness (And as well as efficiency.)
What does this mean for people with LED backlight screens? Well, simply put, don't run the screen at full brightness in a middle of a desert. If you dynamically adjust your brightness (This will save you power as well, I'll put a post in my T410 Ultra Guide later on this subject) to your surroundings constantly, the LEDs do not have to run at high power! This means they do not need to dissipate as much waste heat, running cooler and with less power being driven through them. This means your backlight remain brighter and more efficient (In terms of lumens/watts consumed.)
A note, modern LEDs (As in the last two to three years) have increased in efficiency and practical lifespan, as well as manufacturing consistency.
Not to fighten anyone, but your LEDs will most likely be heatsinked to the thick metal frame of the LCD as well so they do not suffer from being thermally isolated. They are also most likely an array of smaller, low power LEDs driven at low power for efficiency. (Efficiency rises when LEDs are driven at lower than spec, see manufacturer/supplier specs on power draw curve versus lumens produced.)
LED life ratings are measured as "lifetime until 50% brightness" in the industry. When a LED is said to have a 50,000 hour life, this is when the LED is run in an environment where it is at 25C ("Room temperature") with proper manufacturing and binning. It will be run at its specified forward voltage and current, being adequately cooled. At 50,000 hours, it will reach 50% output.
LEDs that are overdriven (! Voltage and current too high) and/or often inadequately cooled have much shorter lifespans to 50% or even death! This can be low as a THOUSAND (1,000) HOURS!
However, LEDs run at lower than full power and adequately cooled can often exceed their expected lifetime specs. LEDs do not have a "million hours" of practical life. Numbers such as "100,000 hours" are very lax estimates of what they practically are at full power. Realistic numbers closer to the lower tens of thousands will be what you can expect from a LED until 50% loss of brightness (And as well as efficiency.)
What does this mean for people with LED backlight screens? Well, simply put, don't run the screen at full brightness in a middle of a desert. If you dynamically adjust your brightness (This will save you power as well, I'll put a post in my T410 Ultra Guide later on this subject) to your surroundings constantly, the LEDs do not have to run at high power! This means they do not need to dissipate as much waste heat, running cooler and with less power being driven through them. This means your backlight remain brighter and more efficient (In terms of lumens/watts consumed.)
A note, modern LEDs (As in the last two to three years) have increased in efficiency and practical lifespan, as well as manufacturing consistency.
Not to fighten anyone, but your LEDs will most likely be heatsinked to the thick metal frame of the LCD as well so they do not suffer from being thermally isolated. They are also most likely an array of smaller, low power LEDs driven at low power for efficiency. (Efficiency rises when LEDs are driven at lower than spec, see manufacturer/supplier specs on power draw curve versus lumens produced.)
