fellow AT members told me to post here instead of off-topic
Is it true ?
or there is just less compared to CRT ?
Is it true ?
or there is just less compared to CRT ?
LCD = 0 radiation ?
- Thread starter jimmyhaha
- Start date
radiation is a very vague term, technicaly if you step outside you are being completely bombarded by solar radiation
only kind of radiation that is truly that dangerous is nuclear radiation such as alpha or beta particles (by that dangerous i mean like hard core damage in short period of time, not like getting skin cancer after 10 years)
only kind of radiation that is truly that dangerous is nuclear radiation such as alpha or beta particles (by that dangerous i mean like hard core damage in short period of time, not like getting skin cancer after 10 years)
Assuming that the kind of radiation you're referring to is low-frequency radiation, then you're nearly correct. LCD screens are nearly 'radiation-free' compared to CRT's.
Demon-Xanth
Lifer
- Feb 15, 2000
- 20,551
- 2
- 81
ANY device that is carring electrical current has some electromagnetic radiation. Monitors, toasters, electric watches, you name it. CRTs just have a noticibly higher amount of radiation due to how they work and it tends to be picked on because of the high frequency whine.
...yes, there is EM radiation coming from the wires in your walls.
Stuff with motors is typically the worst when it comes to EM radiation.
...yes, there is EM radiation coming from the wires in your walls.
Stuff with motors is typically the worst when it comes to EM radiation.
<< ANY device that is carring electrical current has some electromagnetic radiation. Monitors, toasters, electric watches, you name it. CRTs just have a noticibly higher amount of radiation due to how they work and it tends to be picked on because of the high frequency whine. >>
That's correct, further, you are already swamp by Earth's own EM field whereever you are.
I got the cheapest 15'' LCD on the market that I could find at the time, it was labelled as 99% radiation-free!
Ooh that makes me feel good, except it makes me go half blind cos the max refresh rate is 60Hz.
Apart from that, it is a hell of a lot less strain on the ole brain/eyes than a CRT
Ooh that makes me feel good, except it makes me go half blind cos the max refresh rate is 60Hz.
Apart from that, it is a hell of a lot less strain on the ole brain/eyes than a CRT
<< I got the cheapest 15'' LCD on the market that I could find at the time, it was labelled as 99% radiation-free!
Ooh that makes me feel good, except it makes me go half blind cos the max refresh rate is 60Hz.
Apart from that, it is a hell of a lot less strain on the ole brain/eyes than a CRT >>
Huh? I don't see how a 60hz refresh rate would be a problem on an lcd since the image doesn't really go away until after the next redraw. That's one of the drawbacks of lcd screens.
Personally, I don't have a problem with 60hz on any screen. I can't even tell the difference.
<< fellow AT members told me to post here instead of off-topic
Is it true ?
or there is just less compared to CRT ? >>
You can be assured that LCD is free of most harmful ionizing radiation. Ionizing radiation(notably) is emitted in presence of high potential difference in a vacuum.(which is found in CRT) The higher the potential difference, the higher the keV of the radiation.
LCDs don't flicker, regardless of refresh rate. CRTs do because the luminescence triggered in a display pixel by the electron beam fades away
until the beam passes by that spot again. LCDs are different - the entire surface is constantly lit, and each pixel consists of an LC transistor that
either lets that light pass through or not.
If an LCD appears to flicker anyway, then the light tube inside operates at a frequency close to that of the room lighting.
Back to the original question, yes and no. There aren't any strong magnetic fields inside an LCD unit, but there are high voltages (for the backlight).
Electromagnetic radiation and electrostatic effects are drastically reduced from CRTs, but claiming any percentage of "radiation free" is marketing bullshit.
regards, Peter
until the beam passes by that spot again. LCDs are different - the entire surface is constantly lit, and each pixel consists of an LC transistor that
either lets that light pass through or not.
If an LCD appears to flicker anyway, then the light tube inside operates at a frequency close to that of the room lighting.
Back to the original question, yes and no. There aren't any strong magnetic fields inside an LCD unit, but there are high voltages (for the backlight).
Electromagnetic radiation and electrostatic effects are drastically reduced from CRTs, but claiming any percentage of "radiation free" is marketing bullshit.
regards, Peter
Im a little confused about the no flicker thing on LCDs. Don't LCDs us a backlight and don't most lights flicker on and of at something like 60 or 120 Hz. im talking about ordinary house lights here.
<< Im a little confused about the no flicker thing on LCDs. Don't LCDs us a backlight and don't most lights flicker on and of at something like 60 or 120 Hz. im talking about ordinary house lights here. >>
Those backlights are cold cathode lamp operating at 10's of KHz, therefore you will not notice any light flickering.
Jerboy,
Those CCFL inverters typically run from 30-120KHz, 68KHz being closest to typical. If the display can be dimmed, the dimming is usually accomplished by PWM(Pulse Width Modulation). This means that the HV section of the inverter is turned on and off. Often this is synchronized to the refresh. So, yes, he could see flicker. Better inverters will PWM at an exact multiple of the refresh and it is much easier on the eyes. If it is of the non-sychronized type, you will often see banding/rolling patterns at certain "tones" of different colors.
Oh, yeah, CCFL (cold cathode fluorescent lamp) and a inverter creates the HV to light the bulbs.
As far as radiation, the levels compared to a CRT are much lower, for the frequency ranges considered harmful. However, at the data clock rate, a LCD will often have significant radiation from 20MHz-60MHz and at harmonics of the data clock.
Okay, so several here will probably question my answer, so here is what I do for a living:
http://www.upsat.com/mx20_gen.shtml
http://www.upsat.com/at2000_trans.shtml
I am the Product Development Engineer on those, and yes, those are Active Matrix Thin Film Transistor (AM-TFT) LCD displays.
Those CCFL inverters typically run from 30-120KHz, 68KHz being closest to typical. If the display can be dimmed, the dimming is usually accomplished by PWM(Pulse Width Modulation). This means that the HV section of the inverter is turned on and off. Often this is synchronized to the refresh. So, yes, he could see flicker. Better inverters will PWM at an exact multiple of the refresh and it is much easier on the eyes. If it is of the non-sychronized type, you will often see banding/rolling patterns at certain "tones" of different colors.
Oh, yeah, CCFL (cold cathode fluorescent lamp) and a inverter creates the HV to light the bulbs.
As far as radiation, the levels compared to a CRT are much lower, for the frequency ranges considered harmful. However, at the data clock rate, a LCD will often have significant radiation from 20MHz-60MHz and at harmonics of the data clock.
Okay, so several here will probably question my answer, so here is what I do for a living:
http://www.upsat.com/mx20_gen.shtml
http://www.upsat.com/at2000_trans.shtml
I am the Product Development Engineer on those, and yes, those are Active Matrix Thin Film Transistor (AM-TFT) LCD displays.
<< Jerboy,
Those CCFL inverters typically run from 30-120KHz, 68KHz being closest to typical. If the display can be dimmed, the dimming is usually accomplished by PWM(Pulse Width Modulation). This means that the HV section of the inverter is turned on and off. Often this is synchronized to the refresh. So, yes, he could see flicker. Better inverters will PWM at an exact multiple of the refresh and it is much easier on the eyes. If it is of the non-sychronized type, you will often see banding/rolling patterns at certain "tones" of different colors. >>
Actually the cold cathode lamp found in laptops use similar phosphor as standard fluorecent lamps so I would think high frequency flicker is smoothed out very well by the phosphorescence effect of the phosphor. The phosphor will emit visible light when struck with ultraviolet light and continues to glow after power is removed. You can see that a fluorescent lamp glows dim green after it's turned off. Have you ever seen a green neon lamp? It is a regular neon with phosphor inside to produce green light. When powered on 60Hz power and you swing it from side to side, it does not appear dotty, because phosphorescence smooth it out. Regular orange neon lamp is direct light and appears dotty. Anyway you're probably more knowledgeable on this than I am.
The high voltage pulse from inverter can produce RF noise, but no ionizing radiation(most dangerous). Ionizing radiation can only be made from vacuum tube such as CRT and traditional vacuum tubes. Gas filled tubes such as neon and fluorescent doesn't produce any.
<<
Oh, yeah, CCFL (cold cathode fluorescent lamp) and a inverter creates the HV to light the bulbs.
As far as radiation, the levels compared to a CRT are much lower, for the frequency ranges considered harmful. However, at the data clock rate, a LCD will often have significant radiation from 20MHz-60MHz and at harmonics of the data clock.
Okay, so several here will probably question my answer, so here is what I do for a living:
http://www.upsat.com/mx20_gen.shtml
http://www.upsat.com/at2000_trans.shtml
I am the Product Development Engineer on those, and yes, those are Active Matrix Thin Film Transistor (AM-TFT) LCD displays. >>
Jerboy,
The phosphor decay/rise time in CCFL lamps is quite quick, and even at 180 Hz PWM frequencies, I can easily measure the flicker with nothing more than a standard photocell/photodiode and an oscilloscope or frequency counter.
Oh, and NO the phosphor is quite different from a standard fluorescent lamp. I've actually researched the stuff and had our lamps made with different mixes than a normal laptop CCFL, and neither are very close to a standard fluorescent lamp. A very simple test will even show you this. Look at the emitted spectrum bands in the light produced. (You know, like you did back in high school, during chemistry or physics class, with the bunsen burners and loops and chemicals).
Humm, sorry pal, I've spent months in the dark working with CCFL tubes and they absolutely do not glow once they are turned off. Hows that, you say? I've spent many hours dimming bulbs to super low levels, looking at the raw bulb, and changing my circuit design, and looking at the effects. It is a different phosphor. I do know what you are talking about though, because while I was designing a HCFL (Hot Cathode) inverter, durning the early stages of the circuit design I used a standard T-12 fluorescent lamp and I saw the glow you are talking about after I shut it off. After I switched to an Avionics grade HCFL (http://www.thomaselectronics.com/flamps1.html), I had to change my photosensor circuitry do deal with the faster rise and fall times of the phosphors so the loop would not go into oscillation.
Yes, poorly designed inverters can produce lots of RF radiation, along with the bulbs. Well, at least enough that you have to deal with it during EMI testing. Same thing with TFT LCDs. I know, I've been there, done that.
The phosphor decay/rise time in CCFL lamps is quite quick, and even at 180 Hz PWM frequencies, I can easily measure the flicker with nothing more than a standard photocell/photodiode and an oscilloscope or frequency counter.
Oh, and NO the phosphor is quite different from a standard fluorescent lamp. I've actually researched the stuff and had our lamps made with different mixes than a normal laptop CCFL, and neither are very close to a standard fluorescent lamp. A very simple test will even show you this. Look at the emitted spectrum bands in the light produced. (You know, like you did back in high school, during chemistry or physics class, with the bunsen burners and loops and chemicals).
Humm, sorry pal, I've spent months in the dark working with CCFL tubes and they absolutely do not glow once they are turned off. Hows that, you say? I've spent many hours dimming bulbs to super low levels, looking at the raw bulb, and changing my circuit design, and looking at the effects. It is a different phosphor. I do know what you are talking about though, because while I was designing a HCFL (Hot Cathode) inverter, durning the early stages of the circuit design I used a standard T-12 fluorescent lamp and I saw the glow you are talking about after I shut it off. After I switched to an Avionics grade HCFL (http://www.thomaselectronics.com/flamps1.html), I had to change my photosensor circuitry do deal with the faster rise and fall times of the phosphors so the loop would not go into oscillation.
Yes, poorly designed inverters can produce lots of RF radiation, along with the bulbs. Well, at least enough that you have to deal with it during EMI testing. Same thing with TFT LCDs. I know, I've been there, done that.
<< Jerboy,
The phosphor decay/rise time in CCFL lamps is quite quick, and even at 180 Hz PWM frequencies, I can easily measure the flicker with nothing more than a standard photocell/photodiode and an oscilloscope or frequency counter. >>
Oh I see. Different phosphor changes the story completely. Looks like the answer is inverter with better dimming algorithm, such as inductors and multiphase output to cover up each phase's drop and timing and inductor size can be adjusted to limit how high can voltage climb on each on cycle.
<<
Oh, and NO the phosphor is quite different from a standard fluorescent lamp. I've actually researched the stuff and had our lamps made with different mixes than a normal laptop CCFL, and neither are very close to a standard fluorescent lamp. A very simple test will even show you this. Look at the emitted spectrum bands in the light produced. (You know, like you did back in high school, during chemistry or physics class, with the bunsen burners and loops and chemicals). >>
Is it using the same concept? Low pressure mercury vapor tube coated with phosphor that luminance when struck with 253.7nm ultraviolet light?
Why not use the same phosphor used on full spectrum T8 fluorescent lamps?
<<
Humm, sorry pal, I've spent months in the dark working with CCFL tubes and they absolutely do not glow once they are turned off. Hows that, you say? I've spent many hours dimming bulbs to super low levels, looking at the raw bulb, and changing my circuit design, and looking at the effects. It is a different phosphor. I do know what you are talking about though, because while I was designing a HCFL (Hot Cathode) inverter, durning the early stages of the circuit design I used a standard T-12 fluorescent lamp and I saw the glow you are talking about after I shut it off. After I switched to an Avionics grade HCFL (http://www.thomaselectronics.com/flamps1.html), I had to change my photosensor circuitry do deal with the faster rise and fall times of the phosphors so the loop would not go into oscillation.
>>
I don't see how dual lamp setup with each lamp operating on different phase to cover up the flicker of each other. Ofcourse that means more $$$ and they're working hard to cut every corners possible to make it as cheap as possible. Talk about engineering where lowest cost is the highest priority.
>Oh I see. Different phosphor changes the story completely. Looks like the
>answer is inverter with better dimming algorithm, such as inductors and
>multiphase output to cover up each phase's drop and timing and inductor
>size can be adjusted to limit how high can voltage climb on each on cycle.
Nope. The lamps are ran with AC not DC. This would not work with DC
because the materials would acculuate in one side of the lamp, thus
quickly destroying it.
Also remember that the lamp is not infinitely dimable. There is a minimum
strike voltage for one thing. Also, the lower the frequency you PWM at, the
more you can dim a bulb, since there is also a minimum lifetime of carriers
and plasma. There are a whole bag of more tricks out there, inverters that
we design can do 2000:1 dimming ratios reliably, even in the cold.
>Is it using the same concept? Low pressure mercury vapor tube coated with phosphor that luminance when >struck with 253.7nm ultraviolet light?
Basically yes, main difference is that the cathodes are not pre-heated like you
find in normal fluorescent lamps, thus they are called CCFL. Their surface is typically
coated with stronium to allow better transfer of energy.
>Why not use the same phosphor used on full spectrum T8 fluorescent lamps?
Because an LCD has color filters, red, green, blue. They use a tri-phosphor mix
optimized to best match with the color filters for maximum efficiency.
>I don't see how dual lamp setup with each lamp operating on different phase to cover up the flicker of each >other. Ofcourse that means more $$$ and they're working hard to cut every corners possible to make it as >cheap as possible. Talk about engineering where lowest cost is the highest priority.
Yup, dual lamp setup working on different phases works. Too expensive when they are trying to get every single nickle and dime they can. Hey, high volume is a dog eat dog situation.
Newer LED technology backlights are great in many ways. The main problem is that they are quite expensive.
Many of the fundamental drawbacks of CCFLs are not present in a LED backlight.
The link to my AT-2000 product is an example of a unit with a LED backlight. It is limited to 200 fL (685.25 cd/m^2 (or othwise known as nits) light output to extend the life of the LEDs. It will easily do 450 fL(1541.81659483593 cd/m^2 (or othwise known as nits) without overdriving the LEDs whatsoever.
>answer is inverter with better dimming algorithm, such as inductors and
>multiphase output to cover up each phase's drop and timing and inductor
>size can be adjusted to limit how high can voltage climb on each on cycle.
Nope. The lamps are ran with AC not DC. This would not work with DC
because the materials would acculuate in one side of the lamp, thus
quickly destroying it.
Also remember that the lamp is not infinitely dimable. There is a minimum
strike voltage for one thing. Also, the lower the frequency you PWM at, the
more you can dim a bulb, since there is also a minimum lifetime of carriers
and plasma. There are a whole bag of more tricks out there, inverters that
we design can do 2000:1 dimming ratios reliably, even in the cold.
>Is it using the same concept? Low pressure mercury vapor tube coated with phosphor that luminance when >struck with 253.7nm ultraviolet light?
Basically yes, main difference is that the cathodes are not pre-heated like you
find in normal fluorescent lamps, thus they are called CCFL. Their surface is typically
coated with stronium to allow better transfer of energy.
>Why not use the same phosphor used on full spectrum T8 fluorescent lamps?
Because an LCD has color filters, red, green, blue. They use a tri-phosphor mix
optimized to best match with the color filters for maximum efficiency.
>I don't see how dual lamp setup with each lamp operating on different phase to cover up the flicker of each >other. Ofcourse that means more $$$ and they're working hard to cut every corners possible to make it as >cheap as possible. Talk about engineering where lowest cost is the highest priority.
Yup, dual lamp setup working on different phases works. Too expensive when they are trying to get every single nickle and dime they can. Hey, high volume is a dog eat dog situation.
Newer LED technology backlights are great in many ways. The main problem is that they are quite expensive.
Many of the fundamental drawbacks of CCFLs are not present in a LED backlight.
The link to my AT-2000 product is an example of a unit with a LED backlight. It is limited to 200 fL (685.25 cd/m^2 (or othwise known as nits) light output to extend the life of the LEDs. It will easily do 450 fL(1541.81659483593 cd/m^2 (or othwise known as nits) without overdriving the LEDs whatsoever.
<< Also remember that the lamp is not infinitely dimable. >>
Yea I know how difficult it is to dim a fluorescent lamp without causing flicker.
<< Basically yes, main difference is that the cathodes are not pre-heated like you
find in normal fluorescent lamps, thus they are called CCFL. Their surface is typically
coated with stronium to allow better transfer of energy. >>
I guess I'd call it "mini neon signs"
<<
Because an LCD has color filters, red, green, blue. They use a tri-phosphor mix
optimized to best match with the color filters for maximum efficiency. >>
They do make hot cathode lamp with tri-phosphor. Some has CRI of 95, color temp about 6500K
<<
Newer LED technology backlights are great in many ways. The main problem is that they are quite expensive.
Many of the fundamental drawbacks of CCFLs are not present in a LED backlight. >>
The only problem is, LED totally suck at CRI. Everything look so pale and gross in LED illumination.
In addition to thanking you all for an interesting read, I'd also like to thank you for not writing "LCD display". It's a pet peeve of mine, and I can't stand when I see it in technical documentation, of all places!
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