# Why don't humans glow in the dark?

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• blizzardof96
In summary, the human body emits energy, and we don't glow in the dark because we're aren't hot enough to radiate visible light - it's all infrared, which our eyes don't pick up.
blizzardof96
Lets assume:
emissivity of a human=0.91
T=310K
Surface area body: 1.60 m^2

If we use the Stefan-Boltzmann Law we can find a value for the rate of emission of light by a human.

Rate emission=762 J/s

Given this rate of emission, why don't humans glow in the dark?

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blizzardof96 said:
Given this rate of emission, why don't humans glow in the dark?

The EM radiation emitted by humans is almost entirely in the far IR range. Hence we can't see it except on special IR cameras.

davenn
blizzardof96 said:
Rate emission=762 J/s
That looks a bit high. The energy produced by human metabolism is if I recall properly typically somewhere a bit below 100 J/s, and at equilibrium (that is, not on the way to heatstroke or hypothermia) the energy ou has to equal the energy generated.

But in any case, @Drakkith has the answer. The human body emits energy, and we don't glow in the dark because we're aren't hot enough to radiate visible light - it's all infrared, which our eyes don't pick up.

tech99
Nugatory said:
That looks a bit high. The energy produced by human metabolism is if I recall properly typically somewhere a bit below 100 J/s, and at equilibrium (that is, not on the way to heatstroke or hypothermia) the energy ou has to equal the energy generated.

Does this take into account the fact that we're surrounded by an environment of approximately equal temperature that's radiating back at us, so we're not actually losing that much energy?

russ_watters
And of course the body also radiates microwaves, especially my brain, I found. It has been suggested that our own microwave emission exceeds safety limits!

berkeman
Drakkith said:
Does this take into account the fact that we're surrounded by an environment of approximately equal temperature that's radiating back at us, so we're not actually losing that much energy?
Ah - you're right - thx.

blizzardof96 said:
Given this rate of emission, why don't humans glow in the dark?

They do! Your eye is a poor detector that cannot detect this "glow".

And oh, wait till you find out that the human body, on average, also emits about 0.3 mSv per year from the radionuclides in our bodies. We definitely "glow in the dark"!

Zz.

+1
And a number of nocturnal animals can 'see' the bodies of mammals under conditions that humans would describe as darkness. See this link about various snakes that hunt at night. As far as these snakes re concerned, we "glow".

pinball1970

## 1. Why do some animals and plants glow in the dark, but not humans?

The ability to glow in the dark, also known as bioluminescence, is a complex process that requires specific biological structures and chemical reactions. While some animals and plants have evolved to produce their own light, humans do not have these structures and do not possess the necessary genes to produce bioluminescence.

## 2. Is there any scientific reason why humans can't glow in the dark?

Yes, there is a scientific reason why humans cannot naturally glow in the dark. The genes responsible for bioluminescence have not been present in the human genome for millions of years. Even if we were to introduce these genes, it is unlikely that humans would be able to produce enough light to be visible in the dark due to our size and physiology.

## 3. Can humans be genetically modified to glow in the dark?

While it is theoretically possible to introduce bioluminescence genes into humans through genetic modification, it is currently not feasible or ethical to do so. Genetic modification is a complex and risky process, and there is no guarantee that the modified genes would successfully produce bioluminescence. Additionally, the potential consequences and ethical implications of creating bioluminescent humans are unknown.

## 4. Is it possible for humans to produce light in other ways?

Humans do have the ability to produce light through technology, such as using electricity to create light bulbs or using chemical reactions to create glow sticks. However, these sources of light are external and do not involve the body's own biological processes. Humans do not possess the necessary structures or mechanisms to produce light internally.

## 5. Are there any potential benefits to humans glowing in the dark?

In theory, being able to produce light could have certain advantages for humans, such as being able to see and navigate in the dark without the use of external light sources. However, there are also potential drawbacks, such as attracting unwanted attention or disrupting natural ecosystems. Ultimately, the absence of bioluminescence in humans is not a significant disadvantage and does not impact our ability to survive and thrive as a species.

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