Increase in Wavelength of an LED Immersed in Liquid Nitrogen

In summary, the speaker has been conducting an experiment involving dipping LEDs into liquid nitrogen and noting the color change. While online sources predict a decrease in wavelength, the speaker has observed a sudden decrease followed by an increase. They are seeking an explanation for this opposite effect on StackExchange.
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caleb5040
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Hi,

I've been working on an experiment where I dip LEDs into liquid nitrogen and note the color change. All online sources I've seen predict that the wavelength of the light emitted by the LED will decrease upon immersion.
What I've been observing, however, is a sudden decrease in wavelength followed by a definite increase in wavelength. So, for example, a yellow LED turned green-ish at first, and then rapidly changed to yellow-orange.

I've been looking around for an explanation of why I am getting this (opposite) effect, but haven't had any luck. Does anyone have any ideas?
 
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1. What is the reason for the increase in wavelength of an LED when immersed in liquid nitrogen?

The increase in wavelength of an LED when immersed in liquid nitrogen is due to the phenomenon known as thermal expansion. When the temperature of a material decreases, its molecules move slower and become more densely packed, causing the material to expand. This expansion results in a longer distance between the atoms, which in turn leads to a longer wavelength of light being emitted by the LED.

2. How much does the wavelength of an LED change when immersed in liquid nitrogen?

The exact amount of wavelength change in an LED when immersed in liquid nitrogen will vary depending on the specific LED and the temperature of the liquid nitrogen. However, on average, the LED's wavelength can increase by up to 1 nanometer for every 10 degrees Celsius decrease in temperature.

3. Will the increase in wavelength affect the brightness of the LED?

Yes, the increase in wavelength will also affect the brightness of the LED. As the wavelength increases, the energy of the emitted photons decreases, resulting in a decrease in brightness. However, this decrease in brightness is often negligible and may not be noticeable to the human eye.

4. How does the increase in wavelength affect the color of the LED?

The increase in wavelength will cause a shift in the color of the LED. As the wavelength increases, the color of the LED will shift towards the red end of the visible spectrum. This means that the LED will appear to emit a warmer color when immersed in liquid nitrogen.

5. Is there any potential damage to the LED when subjected to extreme temperatures like liquid nitrogen?

Yes, subjecting an LED to extreme temperatures like liquid nitrogen can potentially cause damage to the LED. The rapid change in temperature can cause thermal stress on the LED, which can lead to cracks or other damage. It is important to follow proper safety precautions and handle the LED carefully to avoid any potential damage.

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