How bad is PWM in monitors?

[johnnyTheMac]

Is it true that it is bad for your health and that most newer models have it? Is there a way to disable it? Can you get monitors without it? I just received my ASUS PB238Q and learned that it uses PWM for backlighting. I am wondering if I should take it back now and look for other options.

 

Thanks!

 

 

[lapris54]

Is it true that it is bad for your health and that most newer models have it? Is there a way to disable it? Can you get monitors without it? I just received my ASUS PB238Q and learned that it uses PWM for backlighting. I am wondering if I should take it back now and look for other options.

 

Thanks!

PWM in a monitor? I though that's a way to control motors?

[T.Vengeance]

PWM as in that square wave signal? Then yes it's perfectly safe. Your lights flicker at 60hz too so it's no different than your lamps.

[Joshyy]

Huh? Pulse Width Modulation? It's in fans, I don't think it'll kill you.

[Imabigmac]

There are alternatives, but not everyone is affected by it.

[T.Vengeance]

PWM in a monitor? I though that's a way to control motors?

I guess it could be used in the same respect for LED brightness too.

[Jaybird]

Pwm is not an object. It is a form of voltage regulation. while some fan controllers rely on a voltage regulation through set volts, PWM allows for a more precise voltage regulations. this also allows you to monitor your fan speed. 

 

http://en.wikipedia.org/wiki/Pulse-width_modulation

[johnnyTheMac]

Thank you for the responses everyone. I changed the title because there seems to be some confusion about the subject of the thread.

 

I have a brand new Asus PB238Q sitting right here, but I am debating on whether to send it back or not. I keep reading about backlight PWM frequencies and how some people are getting migraines and eye strain from it. That is way I am concerned. I just didn't realize that this was an issue until I went researching a new monitor.

[RatedBlam]

Pwm in monitors is used to control backlight I believe.

Shouldn't be bad for you but you might be sensitive for it.

And the new dell p series monitors(at least some of them) use an actual dimming circuit not PWM.

But and "upgrade" to those might be pointless. Unless you're sensitive to the flicker.

 

And if you havent previously noticed you probably aren't

[GoodBytes]

Not sure what was the original title to get people confused.

But let me clear it up for those who don't know.

They are 2 ways to control the light illumination levels for LED's, which is what most monitors uses today for their back light.

You have an actual dimmer circuit, which allows the LED to stay at a fairly steady illumination level (special equipment required to detect the small variations), and you have, using a PWM (Pulse Width Modulation) method, which flickers the LED full ON and full OFF at a certain rate continuously. Basically, the lower the illumination, the slower the flickering, and at near max, it goes a very rapid rate, and at max, well, it sets the LED full ON all the time.

Actual dimming circuit is costly... well: ""costly"", while PWM method is dirt cheap. PWM controlled backlight is found mostly on lower end monitors, or by monitor manufactures that seek in maximizing profits.

So what's the problem with PWM controlled back light? Well, nothing really. It's not bad per se (well, I don't think they are any studies that check for that), but for some people (it's not a problem for the majority of people), can have trouble reading the screen until screen brightness is increase or set to max, especially if the individual is tired, or have a headache after prolong usage, or while can't identify it, they can sense it, and bothers them. I fall into the last group. I can use a PWM back light screen just fine, but I feel the flickering, and I find it annoying, like I can't focus on what I am doing on the computer properly after using it for several hours.

"But!" you may say: CFL and well: normal fluorescent light, are like PWM, as they have an electrode that fires repeatably at 60Hz, how come you have no problem in office areas, school, or monitors with CFL's/fluorescent light's?

Simple. It does affect me, but only if the CFL is are the crappy one. Most places or my desktop monitor which uses CFL's, does not. The good CFL has a thick layer of phosphor that retain lights properly between the firing of the light electrode. The cheap ones are not in used, as the light output is a green'ish white which makes people skin color look sick and strange. Also, they burn out faster, as the rest of the light is made of inferior quality. So no one in the office space or schools, or stores, buys them. They were used on low end, especially budget class monitors however (I mean, all the manufacture cares is that it passes it's 1 year warranty).

Similarly for CRT monitors. My CRT monitor's was like looking a nice high-end LCD monitor, while everywhere else it was a flickering mess? Why? because we got good ones where at 75Hz, and even better 85Hz, the monitor provided a steady flicker free image due to the high grade phosphor layer. Mind you, the monitors were not cheap, hence why most people didn't have them. It didn't help for the fact that back them 1500$ didn't really get you a gaming computer.. you had to spend a lot more.

[johnnyTheMac]

Not sure what was the original title to get people confused.

But let me clear it up for those who don't know.

They are 2 ways to control the light illumination levels for LED's, which is what most monitors uses today for their back light.

You have an actual dimmer circuit, which allows the LED to stay at a fairly steady illumination level (special equipment required to detect the small variations), and you have, using a PWM (Pulse Width Modulation) method, which flickers the LED full ON and full OFF at a certain rate continuously. Basically, the lower the illumination, the slower the flickering, and at near max, it goes a very rapid rate, and at max, well, it sets the LED full ON all the time.

Actual dimming circuit is costly... well: ""costly"", while PWM method is dirt cheap. PWM controlled backlight is found mostly on lower end monitors, or by monitor manufactures that seek in maximizing profits.

So what's the problem with PWM controlled back light? Well, nothing really. It's not bad per se (well, I don't think they are any studies that check for that), but for some people (it's not a problem for the majority of people), can have trouble reading the screen until screen brightness is increase or set to max, especially if the individual is tired, or have a headache after prolong usage, or while can't identify it, they can sense it, and bothers them. I fall into the last group. I can use a PWM back light screen just fine, but I feel the flickering, and I find it annoying, like I can't focus on what I am doing on the computer properly after using it for several hours.

"But!" you may say: CFL and well: normal fluorescent light, are like PWM, as they have an electrode that fires repeatably at 60Hz, how come you have no problem in office areas, school, or monitors with CFL's/fluorescent light's?

Simple. It does affect me, but only if the CFL is are the crappy one. Most places or my desktop monitor which uses CFL's, does not. The good CFL has a thick layer of phosphor that retain lights properly between the firing of the light electrode. The cheap ones are not in used, as the light output is a green'ish white which makes people skin color look sick and strange. Also, they burn out faster, as the rest of the light is made of inferior quality. So no one in the office space or schools, or stores, buys them. They were used on low end, especially budget class monitors however (I mean, all the manufacture cares is that it passes it's 1 year warranty).

Similarly for CRT monitors. My CRT monitor's was like looking a nice high-end LCD monitor, while everywhere else it was a flickering mess? Why? because we got good ones where at 75Hz, and even better 85Hz, the monitor provided a steady flicker free image due to the high grade phosphor layer. Mind you, the monitors were not cheap, hence why most people didn't have them. It didn't help for the fact that back them 1500$ didn't really get you a gaming computer.. you had to spend a lot more.

Wow! Thank you for a very informative post. What is considered a low-end monitor? I mean, specifically, does the ASUS PB238Q fall into that category? Am I just overthinking this entire thing? I have read some positive reviews about it, but there are some not so positive ones, too. However, I guess you can find that with anything.

 

I am just trying to decide if I made a good choice. I know that to a certain extent it is personal preference, but I cannot test it out until I get home from work.

 

Thanks again!

[GoodBytes]

The ASUS PB238Q or the Dell U2312HM (similar monitor), both uses PWM back light, and they8 are part of the low-end of the high-end consumer grade monitors.

Basically, they were the early affordable, low cost IPS panels. So you have a nice IPS panel, 6-bit panel, not a true 8-bit, but regardless, visibly better in colors than nearly all TN panels (basically, can be compared with the top end TN panels), plus you have IPS panel advantages, such as reduce back light bleeding, back light bleeding does not effect colors (just visible on blacks), and wide view angle. You also enjoy a solid monitor with a solid stand, non glossy screen and body, and fully adjustable one for a more comfortable computer experience.

If I am not mistaken, sadly, most ASUS monitor uses a PWM, even their higher ones, while this is not the case for Dell. And Dell jsut started to make their lower end monitor not have a PWM with the Dell P2314H. So, you can see Dell pushing the market.

[johnnyTheMac]

The ASUS PB238Q or the Dell U2312HM (similar monitor), both uses PWM back light, and they8 are part of the low-end of the high-end consumer grade monitors.

Basically, they were the early affordable, low cost IPS panels. So you have a nice IPS panel, 6-bit panel, not a true 8-bit, but regardless, visibly better in colors than nearly all TN panels (basically, can be compared with the top end TN panels), plus you have IPS panel advantages, such as reduce back light bleeding, back light bleeding does not effect colors (just visible on blacks), and wide view angle. You also enjoy a solid monitor with a solid stand, non glossy screen and body, and fully adjustable one for a more comfortable computer experience.

If I am not mistaken, sadly, most ASUS monitor uses a PWM, even their higher ones, while this is not the case for Dell. And Dell jsut started to make their lower end monitor not have a PWM with the Dell P2314H. So, you can see Dell pushing the market.

I did not know that this monitor was not 8 bit. I thought I read that it had a 16.7 million color display. Will this cause gradient banding or anything?

[Tam3n]

I bet you won't notice any difference between PWM and "dimming" backlighted monitors

 

What's your current monitor?

[GoodBytes]

All monitors (ok well, I am talking about the computer monitor we use, ignoring the specialty monitors, for example, EIZO has a medical purpose monitor that can display 1.07 billion shades of grays for mammogram analysis), will display 8-bit colors per channels (red, green and blue are channels) so that would be 2^8 * 2^8 * 2^8 = 256 x 256 x 256 = 16777216 colors -> ~ 16.7 million colors. That is the standard RGB model that has been defined ages ago in the early days of color displays for computers.

On the consumer market you have 6-bit, 8-bit and 10-bit per channel panels (you also have 12, 14 and 16-bit on the professional and specialty monitors).

So how does a 6-bit panel output 8-bit colors? It uses something called Frame Rate Control (FRC) or Advance Frame Rate Control (A-FRC). (i don't know why it's called like that, but you can check that I am correct on how it works)

What it basically does, is that it on a color it can't produce it takes 2 colors that it knows it can switch between the 2 that will emulate the color that it can't produce. (They are other technics, but today, this is what is used, and is the best, due to the fast panels actual response time we have). The "advance" in front of FRC, just means that instead of using a algorithm to guess the missing color and how to replicate it, it uses a color processor and a look up table to really know the specific set of colors to choose.

Normally, the color switch is not visible assuming you have a good monitor with decent actual response time (like you won't see it even on a 16ms response time monitor).

So in result, a true 8-bit panel will get you the best colors, as it doesn't use an algorithm to estimate the color. Is there a visible difference? Well that depends on you. Some don't, others do, and others it's night and day, even if you pull a color calibrator on the 2. Of course, another factor is the manufacture calibration if a manufacture set the red to be pink, blue to be orange, and green to be yellow... welll... Personally, I can see a difference between 6-bit and 8-bit. However, for a 6-bit panel well calibrated, it will take me some time to notice it. Basically, I'll notice it from gradients or something. I don't do color critical work, but I love colors.

For 10-bit panels, well this is interesting. It does 1.7 billion colors, which is very nice, but you need the graphic card (most AMD FirePro's or most Quadro's), use Display Port (well assuming you want a high resolution display), and well the content, as everything assumes 8-bit colors. So you need the software (PhotoShop, for example) and image (RAW picture).

The great majority of 10-bit consumer grade monitors, are 8-bit panel with FRC to emulate the 10-bit colors via A-FRC if you have the hardware.

[LDG]

Huh? Pulse Width Modulation? It's in fans, I don't think it'll kill you.