Dear Sudarson S. Sinha

Thank you for your answer.

but i haven't understood wha tis  the two perpendicular polarizers' use.

i have  find another phenomenon.

when a point light is illumated perpendicularly to the screen, we can only see color strips in two perpendicular direction ,they constuct a cross , not a circle. Does it a film interference? if it is ,why not make a pattern of circle?

thanks, do you need a picture?

The posting and the link describe how a liquid crystal (LC) shutter operates - it does not answer the original question about how two crossed polarizers produce colorful light.  That is because the polarizers do not produce any color - nor does the layer of liquid crystals.  The LC layer does not separate the states of polarization, the polarizer and the analyzer are fixed.  The LC layer has an electrical signal (supplied by the transistors in the web explanation) that rotates the state of polarization of the incoming light so that it will align with the analyzer and be passed out of the display.  There is a transistor for each pixel and a matrix or mosaic of small colored filters (Red, Green, Blue) just as in the phosphors of a cathode ray tube TV.  Because the filters are small, our eyes at normal viewing distance do not resolve them so they are blended.  To produce Red light, one only needs to activate the light through the Red filter.  The stronger the activation current the brighter the color.  To produce other colors one actives more than one transistor-filter pair.  Yellow is produced by Red+Green, Magenta by Red+Blue, Cyan by Blue+Green and White by Red+Green+Blue.  The science to produce these effects was developed in the late 1800s and standardized in the early 1900s.     

 Hello

Sudarson S. Sinha

Thanks for your link, I have understood the constructure of the LCD tv .

as its explanation , the caculator screen is similar to the TV or phone screen, but why i can't see the same patten using the caculator screen(use a beam of light illuminate the screen from outside)

And i also want to ask, the link said when there is electrictiy , the screen is dark , do you think this resonable?

really thank you

Dear Danny Rich

Thank you for your answer.

i think maybe you misunderstood my question

the beam of light  is illuminated  from outside and you can see the patern in the reflection direction.

if you have some idea ,please tell me ,thank you

Chi - You asked about TVs.  All TV are driven by a back illumination.  But there is a law in optics known as Helmholz's law of reciprocity.  It is derived from arguments based in the conservation of energy.  It states that in any closed, linear system, one can interchange the source and detector without affecting the optics.  So lets place a mirror in the place of backlight and place a diffuse or directional white light in illumination space near your eyes.  Then the light will pass through the polarizer, through the filter and reflect off the mirror back through the filters and the polarizer which now serves as an analyzer.  The optics are exactly the same and the liquid crystals can block the reflected light or pass the reflected light.  So some simple displays, as in cell phones and PDAs use the reflective LCD to save power.  They are, however, not as bright and efficient as the LED backlight models.

Hi Danny

i understand what your mean, do you think the colorful strip is relevent with color filter?

thank you

Hello Sudarson

do you think this phenonmen is about film interference or reflection diffraction? or the color filter

Hi Sudarson

i have seen the youtube video, why can't i use the polarizers to see it?

Hi Chi,

I did not observe the effect you described yet but I think it could be due to diffraction and interference of the light reflected from the tiny periodic structure of the display surface, similar to color effects in the light reflected from the surface of optical discs. It seems that smooth surface is necessary for observing such effect. Matt finish of display surfaces may not only suppress unwanted reflections, but also crush interference conditions.

Hi Jan

i think you are right, but i have one more question, if this phenmenon is like we observe on the disc, why the colorful strip don't change when i change my observation view of rotate the LCD screen.

you can try to use a light source, illumate your computer screen, you may see the patern

thank you.

Hi  Sudarson

i am really thank you for your patient answer, but I am sorry that i can't totally understand what you mean, do you think this is near to the phenomenon of disc or this phenonmen is only about the polorizers

thank you

HI Sudarson

I have done as you said. In these three condition, i observe the same color band.

and when i move away , i don't see it become less intense.

Is it because i stay too near?

thank you

Hi Sudarson 

do you see the phenomenon like this ?

different mobile phone have different color band. but when i move the phone from the source ,i didn't notice it move.is it because i haven't moved enough?

thank you

Hi Sudarson

IF i rotate the screen ,the pattern will change, the strip will nearly disappear.

Do you think this diffraction is caused by the pixel of the alignment layer?

Do you have some article or link about the screen structure of phone ?

thank you very much

HI Sudarson 

I try to take a clear picture, but the white light is to intense.

this is piture is use a point light, the pattern is very beautiful,you can try it yourself.

i think it's about the pixel's diffraction.Do you think so?

thank you very much

Hi Sudarson 

what the other  factos' effect, are they significant?

Thank you very much