The Mystery of Human Luminosity: A Comparison to Daily Energy Intake

In summary, the conversation discusses the calculation of a human's luminosity as compared to the daily energy received from eating. The resulting calculation shows that a human radiates more energy than they consume, which leads to the question of how a human maintains a comfortable temperature. The conversation also mentions the difference between the scientific and layman's use of the term "calorie" and suggests looking into this discrepancy.
  • #1
Xalkias
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Homework Statement


If we assume that a human radiates like a black body, calculate the luminosity in watts, then compare it to the daily energy a human gets from eating. (The area of a human A=1.3 m2)

The Attempt at a Solution


The temperature of a human is 310K so L=AσT4 = 1.4*5.6*10-8*(310)4=733 watts and the average energy of a human gets from eating is about 3000 calories=12500 joules.
So in one day a human seems to radiate too much energy compared to the daily energy he gets. What is going on?
 
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  • #2
Xalkias said:
What is going on?
Let's say you're not looking at a human, but at a rock. It gets zero Joules from eating. How come it stays at a comfy 30-ish degrees centigrade on a warm day?
 
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  • #3
Xalkias said:
...3000 calories=12500 joules.
... What is going on?
Along with paying attention to Bandersnatch's comment, you might also want to look into the sciency vs laymanish use of the word "calorie".

hint: They have two different values.

ps. I'm going to ignore your "area" typo, as it's not that big a deal.
 

1. What is the luminosity of a human?

The luminosity of a human refers to the amount of light that a person emits or reflects at any given time. It is measured in units of watts or lumens.

2. How is the luminosity of a human determined?

The luminosity of a human is determined by the amount of light that is emitted or reflected by the body's surface, primarily from the skin and hair. This can be measured using specialized equipment such as photometers or spectrophotometers.

3. What factors can affect the luminosity of a human?

The luminosity of a human can be affected by various factors such as skin color, body temperature, and clothing. Individuals with lighter skin tones tend to have a higher luminosity compared to those with darker skin tones. Body temperature can also affect luminosity, as a higher body temperature can cause the body to emit more heat. Additionally, the type and color of clothing can also impact luminosity, as light-colored and reflective clothing can increase luminosity.

4. Is the luminosity of a human constant?

No, the luminosity of a human is not constant. It can vary depending on the factors mentioned above, as well as other external factors such as lighting conditions and the environment.

5. How does the luminosity of a human compare to other sources of light?

The luminosity of a human is relatively low compared to other sources of light, such as the sun or artificial lighting. On average, a human emits around 100 watts of light, while the sun emits around 3.8 x 10^26 watts. This is due to the fact that humans are not primarily light-emitting organisms, and our bodies mainly reflect light from other sources.

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