Maybe it's just another "dieselgate"?
My professional notebook computer I got recently shows in the "Lenovo Power Manager" 4 Watts used in the Normal Mode (radios turned on, screen lit 13/15) and 3 Watts in the Airplane Mode (radios turned off, screen dimmed to 3/15) - see attachments.
Well, it's got new 14nm CORE i7 CPU and a solid state disk so they won't probably take too much. There are other components consuming some power. So what's left for the screen backlit?
I haven't got any means to measure the real battery drain but I somehow can't believe those values. It sounds a bit fishy. What do you think?

Easy to test :

 - Wth the battery disconnected, manually set the computer to battery mode and measure current at the power adapter DC input

 - Measure the time it takes for the computer to drain the battery from disconnecting adapter to low battery shut down in this mode. Repeat the experiment and this time plug in the USB port something that draws a few watts but is really precise and constant (such as : short circuited constant-current drive made of a transistor). Compare and do the math (this method is generally wrong since the battery discharge characteristic is non linear, but for very low loads it is fair enough i think). Keep the conditions ie. initial temperatures etc the same in both tests, and let the computer stay "indefinitely" on the adapter before the test start to be sure the battery really is fully charged

How much does the laptop heat ?

Maybe it's just another "dieselgate"?
My professional notebook computer I got recently shows in the "Lenovo Power Manager" 4 Watts used in the Normal Mode (radios turned on, screen lit 13/15) and 3 Watts in the Airplane Mode (radios turned off, screen dimmed to 3/15) - see attachments.
Well, it's got new 14nm CORE i7 CPU and a solid state disk so they won't probably take too much. There are other components consuming some power. So what's left for the screen backlit?
I haven't got any means to measure the real battery drain but I somehow can't believe those values. It sounds a bit fishy. What do you think?

I don't think it's much impressive: consider an battery about 40-50 W/h
Actually it can be the minimum power consumption, because low cpu load etc...

If you do not even move the mouse, with LED backlight it should not be that difficult. You do not need that much brightness, the 10inch screens used no more than 5W CCFL with about 30lm/W for full brightness, while LED's efficacy uses to be now in the 120lm/W range (for the low power devices, typically used with backlight), so about 3W power input at full brightness for a 2x larger screen area would be about equivalent. And as your brightness setting is 3/15, it means less than 1W for the backlight...

@Ash: It doesn't heat much. When used for work that could be compared to a Word document editing (or a little more), the only slightly warmer part is the area above keyboard (near screen joints). The cooling fan starts only when something's compressing etc. The LCD screen is cold for my hand.

@Medved: Didn't know that LED backlit is 4 times more efficient than CCFL one. The main difference I think is the absence of that optical grid(?) transferring the light (more or less evenly) from CCFL tubes on top and bottom of the screen to the pixel array. This might be the main cause of losses. No more needed with flat light emitting diodes behind pixes groups. Moreover, some designs turn off/dim particular LEDs in case there's a black/dark portion of the image above them, thus increasing the contrast. Impossible with CCFL tubes and also more energy saving.
Btw. how was the backlit intensity regulated in case of CCFLs?

With the fan off at all times, slightly warm in 1 spot and room cold elsewhere is consistent with few W power draw

With CCFLs it is usually PWM controlled ie the HF output is modulated on-off at a lower frequency (still invisible as flicker, but sometimes audible as whine from the inverter). Same for the LEDs in the screens where they are in a line along the edge

@Medved: Didn't know that LED backlit is 4 times more efficient than CCFL one.

CCFL has about 40lm/W, the LED's about 100..140lm/W (bare lamps, without ballast losses). Then the optical properties (see below) are responsible for the further system efficacy gain...

The main difference I think is the absence of that optical grid(?) transferring the light (more or less evenly) from CCFL tubes on top and bottom of the screen to the pixel array. This might be the main cause of losses. No more needed with flat light emitting diodes behind pixes groups. Moreover, some designs turn off/dim particular LEDs in case there's a black/dark portion of the image above them, thus increasing the contrast. Impossible with CCFL tubes and also more energy saving.

That method is not usable with thin panel designs like notebooks or tablets or mobile phones. It needs quite thick spacer to allow the light from the individual LED's diffuse into smooth pattern (so it can be handled by the LCD). And even there it requires the LED's to be placed rather close to eachj other - yielding very high number of LED's, so rather high cost. This is used in fixed mount panels, where the required thickness of 10mm or so is of not big problem and the high number of LED's is anyway necessary for the required brightness.

With portable devices I've seen nothing else than a string of LED's at the edge of the panel, like it used to be with the CCFL. But that means about 40% reduction of raw lumen output, as from the CCFL shining all around the tube, only part of the light get utilized to provide the backlight. From the way smaller LED's it is way easier to harvest way bigger portion of the light output

Btw. how was the backlit intensity regulated in case of CCFLs?

Two methods:
Older is using PWM for keying the CCFL inverter, newer method is to really reduce the lamp current by the ballast. In fact combination of both was used.

With LED's it is again a combination of both current reduction, as well as PWM. But the LED's can go way deeper with the output reduction (easily down to 1% or so), the CCFL was limited to about 10..15% when both methods combined (the main problem is the temperature change altering the gas composition, so the light color and bad arc stability or light uniformity at low currents with the CCFL, the LED's do not suffer from any of these issues)

My 3 years old lenovo X220 (i5-2540, 12"screen, ssd) shows in idle (not very easy to have a really idle system with windows 7) these values:
screen at 0 (very very dark)= 6.1W
screen at 12 (standard indoor settings, pretty bright)= 7.1W
screen at 15 (maximum, settings used only outdoor)= 8.6W

The screen is an LCD IPS option with better color/contrat than the standard TN version and stronger backlight (300cd vs 200cd), I think that the power consumption of the standard version would be lower. In any case it seems that the backlight doesn't drawn more than 2.5W

Anyone with CCFL laptops here ?

My 3 years old lenovo X220 (i5-2540, 12"screen, ssd) shows in idle (not very easy to have a really idle system with windows 7) these values:
screen at 0 (very very dark)= 6.1W

The screen is an LCD IPS option with better color/contrat than the standard TN version and stronger backlight (300cd vs 200cd), I think that the power consumption of the standard version would be lower. In any case it seems that the backlight doesn't drawn more than 2.5W

The question is, whether the "0" means really backlight OFF (only that would mean no power for backlight) or just the minimum brightness setting (quite frequent implementation - in reality ithe minimum means something around 20% brightness, and about 30% lamp power)

Otherwise 300Cd for a 14" 4:3 screen means about 18lm from the screen. Given the fact the color filters let pass only 11% of the illumination power (1/3 area occupied by a filter passing 1/3 of the power, so total 1/9 of the power), which could mean about 20% of the lumen output (given the main lm contributor is the green one), it means the panel gets 100lm for it's backlight. That means 3..4W for the CCFLL, pretty inline with the consumption you see.
And the same will easily do a 1W of LED's...

Anyone with CCFL laptops here ?

I used to but don't anymore.  both my desktop monitors are CCFL and both take about 1.5 amps from the wall at 120v.  I always figured the backlighting was most of that but maybe it isn't?  maybe the control circuitry and the LCD panel itself take more than the backlight.   

My oldest laptop, which was bought in 2003, had Ccfl backlighting.

The power supply in the monitors have power factor on the order of 0.5 (atleast on 240V so), so 1.5 * 120 * 0.5 = ~90W. Still unreasonable

The backlight of a desktop monitor is 4 6W..8W CCFLs. that is 30W. Add few W ballast losses, PSU losses and LCD panel/video processing components power. that is about 40W

Perhaps i am wrong with the power factor ?



My few laptops - newest one being a 2007 Thinkpad - are all CCFL

The question is, whether the "0" means really backlight OFF (only that would mean no power for backlight) or just the minimum brightness setting (quite frequent implementation - in reality ithe minimum means something around 20% brightness, and about 30% lamp power)

Otherwise 300Cd for a 14" 4:3 screen means about 18lm from the screen. Given the fact the color filters let pass only 11% of the illumination power (1/3 area occupied by a filter passing 1/3 of the power, so total 1/9 of the power), which could mean about 20% of the lumen output (given the main lm contributor is the green one), it means the panel gets 100lm for it's backlight. That means 3..4W for the CCFLL, pretty inline with the consumption you see.
And the same will easily do a 1W of LED's...

No with 0 the backlight is not completely off, but it's very very dark, it' visible only in the darkness. I think that's the LEDs are powered only a few % of the maximum power. I can also made a measurement with the screen completely off, but this wouldn't be useful because both the LCD control circuitry and part of the video card would be powered off.

Btw I have also a seven years old Lenovo W500 with a 15.4" LCD with 1 ccfl (TN technology, very rubbish compared with the IPS in the X220...)
These are the idle measurements:
screen at 0 (very dark, but not as with the X220)        = 10.8W
screen at max 15 (equal about at setting 12 of the X220) = 15.8W

First the net lumen output goes with square of the diagonal, so a 20" panel will have to glow by double the light output of a 14" screen with the same brightness.

Second the desk top monitors are designed to have perfect color with wide view angle. That means an extra grid of microtubes (usually a form of glass or foil the front). What it does is take the light from the small angle in front of each pixel and then throw it to the required wide angle on the viewer's side. That means excellent picture, but about 80% or more light loss compare to narrow view angle monitor. Full 180deg view angle types may lose easily 90% of the light compare to an equivalent narrow angle notebook monitor.

Then the brightness for a desk top monitor uses to be higher than the power limited portables.
That means for a 300cd 24" panel you may easily end up with a requirement of 600lm or more. With a 40lm/W CCFL's it means 15W lamp.

Plus about 70% efficiency of the backlight inverters, another 70% efficiency of the power supply, so barely 50% efficiency in powering just the backlight, so at least about 30W and we still are not talking about the full 180deg view angle (there it may easily be in the 60W range).
And on top of that is some picture processing power and driving the main LCD array (all the chips tend to be quite hot, by the way), so getting into the 50..90W range total is nothing unusual. Unless you especially select some low power type monitors, but then you should be consent with reduced view angle (but I've personally never needed anything more than +/-30deg, so "paying" 50W of power just to get a view angle I'm not able to use at all because my monitor is placed in a corner, is quite nonsense for me)