LCD TV Power Characteristics

[crashsite]

I wonder if someone here knows about the relative power consumption in an LCD TV or monitor.

As I understand it, there is an EL panel behind a sandwich that consists of polarizing filters, the liquid crystal matrix, a layer of a conductive pattern that transfers energy to the crystal matrix, RGB optical color filters and protecive cover. There's probably some more, such as the transistor matrix for active (the TFT) displays, etc.

The EL panel has a uniform brightness and the pixel brightness we see is due to the amount of twist in the liquid crystal material. Because the cryatal interaction is electrostatic (is it?), when it's in a static state (transmitting light, blocking or in between), it uses almost no power. Thus, the LCD panel should use the most power with a changing picture.

It should be different than a CRT whose pwer is directly proportional to the beam current (pixel brightness). Since the EL panel is on all the time that the set is on, the total power of the set should be pretty constant regardless of whether the screen is light or dark.

But, is that true? Is there a difference in power consumption to hold the pixels light or dark? If so, does it take more power to hold the pixel light or dark? In other words, does the crystal normally pass light or block it when no voltage is applied?

What is the relative amount of power typically consumed in the different parts of an LCD TV or monitor (as divided up among the electronics (power supply, prrocessor, tuner, etc.), LCD twisting circuits and lighting the EL panel)?

 

[kchriste]

On some LCD TVs the EL backlight brightness is adjusted for light vs dark scenes to boost the contrast ratio so it's power consumption may vary. The liquid crystal part of the device draws very little current compared to the back light.

 

[Nigel Goodwin]

The back light isn't an EL panel in a TV, it's a number of flourescent tubes - as already suggested, modern high quality sets dim them on dark scenes to give improved dynamic contrast ratios (and coincidently, reduce power consumption).

As also mentiond, the LCD itself takes next to zero power.

 

[blueroomelectronics]

They do draw less power with the backlight turned down. You should always calibrate your LCD TV else they are way too bright out of the box.

 

[Nigel Goodwin]

They do draw less power with the backlight turned down. You should always calibrate your LCD TV else they are way too bright out of the box.

Most sets come set to Vivid (or similar), this is for demonstration in the shop - obviously the manufacturers think shop staff are too thick to turn it up

Simply setting it to 'Standard' is mostly all you need to do, and the later Sony sets ask during auto-setup if it's for Home or Shop, and set it accordingly.

 

[blueroomelectronics]

Also look for DVDs with calibration videos. Star Wars 3 has a video setup in the menus.

 

[Ubergeek63]

The other thing that happens is that it is hard on the tubes. What I do not know, not having looked into it, is if they have light sensors and adjust accordingly.

 

[Nigel Goodwin]

The other thing that happens is that it is hard on the tubes. What I do not know, not having looked into it, is if they have light sensors and adjust accordingly.

What do you mean 'hard on the tubes'?, obviously it depends how you have the back light set, but they are specced for a similar life to a CRT.

As for sensors, assuming you mean to adjust the contrast/brightness according to how bright the room is, some sets have them, and some sets don't - but it's always been a crappy feature and absolutely useless - even back on the old 1950's B&W sets where it first appeared. If it's there, turn it OFF

 

[Ubergeek63]

Tube life is dependent on intensity and tube ratings, they can be anywhere 10K - 50KHrs and I would not put it past cut rate outfits to cut corners there since it is not expected to be on 24-7 and as long as it does not fail in the warranty period, what do they care?

The brightness control is actually a good feature since it reduces eye strain in dark rooms as well as saving power. The biggest problem with it is that you can only disable it on the ones that I have seen. What is needed is for the customer to be able to set it based on his or her preferences, some might like it to go darker than others in a dark room.

 

[Nigel Goodwin]

Tube life is dependent on intensity and tube ratings, they can be anywhere 10K - 50KHrs and I would not put it past cut rate outfits to cut corners there since it is not expected to be on 24-7 and as long as it does not fail in the warranty period, what do they care?

Most of the cheaper sets will be long gone before the LCD panels reach the end of their life, Plasma's even more so - I've never seen either type 'worn out' yet, but many Plasma's have been scrapped because of PDP faults, or plain lack of spares (such as Fujitsu).

The brightness control is actually a good feature since it reduces eye strain in dark rooms as well as saving power.

I've never seen one yet that wasn't improved (under any conditions) by turning it OFF.

 

[Ubergeek63]

Most of the cheaper sets will be long gone before the LCD panels reach the end of their life, Plasma's even more so - I've never seen either type 'worn out' yet, but many Plasma's have been scrapped because of PDP faults, or plain lack of spares (such as Fujitsu).

The panels have potentially a significantly longer life than the backlights

I've never seen one yet that wasn't improved (under any conditions) by turning it OFF.

You are NOT an eye doctor...nor am I. I do know that it causes eye strain and that it has been commonly accepted for quite some time... and The Lighting Research Center (LRC), part of Rensselaer Polytechnic Institute, did a study that proves it:

New Study Tests The Effects Of Watching TV In A Dark Room

So what it really boils down to is what you think looks better is worse for your eyes and your disposition ( eye strain begets a headache, and a headache begets a foul mood )

 

[Nigel Goodwin]

The panels have potentially a significantly longer life than the backlights

Well PDP's don't have backlights, but they both 'wear out' by the same mechanism - lack of response in the phosphurs that convert UV to visible light. Both drop in brightness drasticlaly over the first few months, and it's this mechanism that makes PDP's prone to screen burn in their early life.

'Potentially' doesn't mean squat sets or panels aren't lasting long enough to get to the 'worn out' stage, but neither have been around long enough for their life span to be reached yet.

You are NOT an eye doctor...nor am I. I do know that it causes eye strain and that it has been commonly accepted for quite some time... and The Lighting Research Center (LRC), part of Rensselaer Polytechnic Institute, did a study that proves it:

New Study Tests The Effects Of Watching TV In A Dark Room

So what it really boils down to is what you think looks better is worse for your eyes and your disposition ( eye strain begets a headache, and a headache begets a foul mood )

So you spend a £1000 on a TV, then set it so it has a crappy picture - I suspect that's more likely to make you miserable

Notice the study is for watching in a dark room! - you shouldn't be watching TV in a dark room to start with, sensors or not.

 

[Ubergeek63]

Well PDP's don't have backlights, but they both 'wear out' by the same mechanism - lack of response in the phosphurs that convert UV to visible light. Both drop in brightness drasticlaly over the first few months, and it's this mechanism that makes PDP's prone to screen burn in their early life.

The topic is not about PDPs therefore your comments about them are irrelevant.

However, since you brought it up... while the wear out mechanism is the same the effect is not. A PDP will also display a screen burn if left on the same image for an extended length of time. An LCD backlight will only display a color shift as the phosphors age at different rates, and that is easily compensated for with a hue and tint type of adjustment.

'Potentially' doesn't mean squat sets or panels aren't lasting long enough to get to the 'worn out' stage, but neither have been around long enough for their life span to be reached yet.

The LCD itself has a very long useful life and the new LED back lit panels will not have the burn in characteristic.

So you spend a £1000 on a TV, then set it so it has a crappy picture - I suspect that's more likely to make you miserable

Notice the study is for watching in a dark room! - you shouldn't be watching TV in a dark room to start with, sensors or not.

Which is what the sensors are for, hence relevant.