Rainbow light reflection on TV from my hand

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Discussion Overview

The discussion revolves around the phenomenon of rainbow light reflections observed on a TV screen from a participant's hand. Participants explore the underlying physics of this effect, considering various optical principles such as diffraction, refraction, and thin film interference. The conversation includes personal experiences and technical explanations related to the observation.

Discussion Character

  • Exploratory
  • Technical explanation
  • Debate/contested

Main Points Raised

  • One participant questions the possibility of observing rainbow reflections without a direct light source, expressing skepticism about paranormal explanations.
  • Another participant suggests that the TV acts as a diffraction grating, where white light from the hand is split into colors due to different angles of reflection.
  • Some participants propose that the observed effect could be due to thin film interference or refraction effects rather than diffraction.
  • There is discussion about the pixel spacing of TVs and whether it is sufficient to cause similar dispersion of wavelengths as seen in traditional diffraction gratings.
  • One participant mentions that certain TV screens have multiple reflective strips within a pixel, which could contribute to the rainbow effect, although they question if a hand would provide enough brightness for this to occur.
  • Another participant emphasizes the need for a bright point source to observe such effects, noting that a wide source might not produce distinct fringes.
  • Technical details about IPS (In Plane Switching) displays and their electrode configurations are shared, explaining how they differ from older LCD technologies.

Areas of Agreement / Disagreement

Participants express a range of views on the cause of the rainbow reflections, with no consensus reached. Some support the diffraction explanation, while others suggest alternative mechanisms like thin film interference or refraction. The discussion remains unresolved regarding the exact nature of the observed phenomenon.

Contextual Notes

Participants note the importance of specific measurements and conditions, such as the distance from the screen and the wavelength of light, which could influence the observed effects. There is also mention of the limitations of visual observations without photographic evidence.

Knifeborn
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TL;DR
Rainbow reflection on my tv from my hand
How is this possible?

Could anyone debunk this by your physics knowledge? Ive seen the other rainbow reflections but they came from direct light sources. I am a buddhist practitioner and Im familiar with the 'Rainbow body' phenomena, but I wouldnt give so easily myself credit of such. There is no direct light to the tv cos I had curtains but although this happened 6 years ago it still leaves me speechless every time I watch it. Im very critical minded person and not the person to go all out with paranormal explanations so I really need your help.

If nothing else, it will trick your sensory input. And yes, there is no after effects or anything at all, only me recording it with my cellphone.
 
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Your TV is a diffraction grating. White(ish) light coming off your hand is a mix of colours of light which reflected from the screen/grating at different angles, so the light is split into a rainbow. You will see the same effect if you use a well illuminated strip of white paper in place of your hand. If you replace it with a same-size piece of red paper in the same place you will see only the red reflections, and similarly with blue paper you will see the blue reflections.

See also https://physics.stackexchange.com/questions/167892/diffraction-pattern-on-lcd-screen.

It's a related phenomenon to the rainbow reflections you see from CDs and DVDs.
 
Thank you for clearing this out for me! Now I dont have to go crazy
 
Ibix said:
Your TV is a diffraction grating.
A diffraction grating has a typical spacing of a few hundred lines per mm. Is the spacing of the pixels small enough to produce a simlilar dispersion of wavelengths? I think it's more likely to be due to a refraction effect or thin film interference between two of the layers.
 
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sophiecentaur said:
A diffraction grating has a typical spacing of a few hundred lines per mm. Is the spacing of the pixels small enough to produce a simlilar dispersion of wavelengths? I think it's more likely to be due to a refraction effect or thin film interference between to of the layers.
You can get diffraction off the millimeter markings on a ruler (well polished metal works best, but I've done it with a plastic one I had to hand) if you tilt it across the beam of a laser pointer, and a TV grid is considerably finer than that.

I guess it could be thin film interference. I think there are several horizontally displaced reflections rather than a halo, though, which makes me think it's something to do with the pixel grid.
 
Ibix said:
You can get diffraction off the millimeter markings on a ruler (well polished metal works best, but I've done it with a plastic one I had to hand) if you tilt it across the beam of a laser pointer, and a TV grid is considerably finer than that.

I guess it could be thin film interference. I think there are several horizontally displaced reflections rather than a halo, though, which makes me think it's something to do with the pixel grid.
I agree it's not certain. We can see diffraction effects all over the place. The angle of dispersion is relevant here. If the OP is just describing coloured edges then we see what can be described as Colour Aberration (in poor lenses for instance. Maybe more details (measurements etc.) of what was seen would produce a more certain diagnosis. A TV screen has liquid crystals in it and off-axis effects could be anyone's guess. This sort of thing affects the contrast range that can be obtained by any display

A purist could say that all optical effects are really down to 'refraction' [Edit I meant diffraction] - the effect of summation of a range of light paths through a system. Refraction can be calculated starting with waves.
 
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Ibix said:
You can get diffraction off the millimeter markings on a ruler (well polished metal works best, but I've done it with a plastic one I had to hand) if you tilt it across the beam of a laser pointer, and a TV grid is considerably finer than that.
But here the tv screen here is not tilted.
Guessing a distance from the screen of 1m, the distance to the first maximum of 0.05 m and light with a wavelength of 600 nm, You need 83 pixels/mm. I think mobile phones come close to that nowadays.

Of course we also need the size of the monitor, and its maximum resolution. The measurement would be much easier with a laser, different colors have different places for the maxima, and it gets messy.

The effect can be easily seen with a cd with a spacing of 1.6 micrometer (625 lines/mm)
 
Some tv-screens, such as LG, have multiple reflective strips (electrodes?) within a pixel. The groove period of these strips is 0.03 mm, so the angle between red maxima is 1° (λ = 600 nm). In some situations that produces a rainbow effect. However you need a bright point source, such as a lamp, to see the rainbow effect. I don't think a hand would be bright enough.

combi.webp


LG-kruis.webp
 
I've seen that sort of thing in many situations but it always needs a bright point / line source. For a wide source, the fringes just add up to nothing except for the edges. I guess we'd need to see a photo of the original observation - else it's just guessing.
Your point about the reflective strips is interesting. what's all that about? Do you have a link?
 
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  • #10
About the reflective strips: "IPS" (In Plane Switching) liquid crystal displays have "interdigital electrodes" within each pixel. That is, multiple electrode strips, and neighbouring strips are connected to opposite poles. As a result the electric field is approximately parallel to the surface of the display. In contrast, the electric field in an older type of LCD display, "twisted nematic", is perpendicular to the surface. An advantage of IPS is its wide viewing angle.

Link: 1 and 2

LCD2.webp
 
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Every day's a school day. Thanks
 

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