Why LED light changes color when dips into liquid nitrogen? Setup is simple we jsut need an LED, a battery as source of power, wires for to complete the circuit and a cup of liquid nitrogen and of course gloves and goggles.
When the lit led is submerged into the liquid nitrogen the color changes, I suppose the lowered temperature affects the flow of electrons hence the resistivity but this shouldn't affect frequency of light no? I mean it should have glow brighter not change color...
 A: For the reasons that would be clear below the answer should consider two cases, at least in principle and without going deep into possible technologically related issues and differences/overlap.
The first case is that of classical semiconductors LEDs. Here the atomic solid bulk determines both transport of charges and emission.
As for another answer and many sources in the web, "The energy bandgap of semiconductors tends to decrease as the temperature is increased. This behaviour can be better understood if one considers that the interatomic spacing increases when the amplitude of the atomic vibrations increases due to the increased thermal energy. This effect is quantified by the linear expansion coefficient of a material. An increased interatomic (italic mine) spacing decreases the potential seen by the electrons in the material, which in turn reduces the size of the energy bandgap." as taken from ref. 1, for example.
Cooling a LED at liquid nitrogen T increases the band-gap and thus results on a higher frequency (energy) of the photons emitted upon electrons and holes recombination.
Notes that the way how electrons would populate the bands and their mobility is a different aspect which should impact on the electrical and luminance characteristics rather than on the emitted colour per se.
The second case in that of organic, molecular LEDs. Here the molecular solid bulk mostly determines the transport properties.
The light emission does not come from electrons and holes recombination in a strict sense. Rather, the latter, leads to the formation of a localized chromophore (an excited molecule or portion of a macromolecule). Is this specific entity that is responsible for the colour of the emitted photons.
Now, if in classical semiconductors with covalent lattices rising the T results in a decrease of the potential seen by the electrons, in organic LED the electrons in a chromophore see at first a local molecular potential, which has a T dependence on its own.
The "band-gap" of organic semiconductors - especially when properties such as light absorption and emission are discussed - is the HOMO-LUMO energy gap. In molecule, this gap is low when extended systems of in-molecule delocalized electrons are present, and it is reduced further as more the delocalisation effectively takes place. See ref. 2 and consider that the same primary structure can lead to a different effective conjugation extent depending on the actual geometrical secondary structure.
The latter has an intrinsic relationship with the geometrical order and flatness of the molecule. Lowering the T hampers molecular motions and internal interbond rotations. As such, opposite to the previous classical case, reducing the T generally reduces the gap, at least when the emissive molecule shows some themochromism in the solid state.
Note that intermolecular effects, thermally dictated or not, can also results in a modulation of the gap. However, a more compact structure will still likely lowers the gap: instead of "pinning" electrons in a lattice it will indirectly orders its constituent, by flattening them for instance.
Again I am considering just the light emission per sé.
The effect of lowering the T might be detrimental if electrical aspect are taken in consideration.
To resume: you can probably tell if the LED of your experiment was inorganic or organic.
Having observed a reddening of the emitted light would points to an OLED, opposite a blue-shift would tell that the LED was an inorganic one.
Little can be said about the light-on potential, brightness, and efficiency, as for these quantities are more convoluted functions of the variables above (and perhaps some more not directly mentioned).
I have not direct practical experience with cooling LEDs. However, the above should be read having the spectra in mind. The colour change should be intended to be substantial or just a nuance. I hardly see the chance for a blue LED to become red, or for the viceversa...

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*https://bit.ly/3j2t08w

*https://en.m.wikipedia.org/wiki/Conjugated_system
A: An LED contains a semiconductor where electrons flow through to generate light. This semiconductor contains a conduction band and a valence band.
Between these bands is a bandgap which represents the difference in energy between the bands. It is this difference that controls the colour of light emitted by the LED (electrons drop from the conduction band to the valence band and then release photons). The size of this drop (bangap), therefore controls the wavelength of the emitted photons.
Now if you put your LED in liquid nitrogen, these electrons will lose thermal energy and the bandgap in the semiconductor increases.  Because of this increase, the electrons dropping from the conduction band falling to the valence band will emit higher energy photons. And because energy, frequency and wavelength of light (photons) are related by
$$E = h \nu = h \frac{c}{\lambda}$$
the emitted photons will have a shorter wavelength. So energy and therefore frequency of the emitted photons are increased when the temperature is brought down, which is sort of counter-intuitive, if you consider (as you did) the effects of temperature on resistivity.
For example, a orange LED might turn yellow, yellow will turn green etc.
