How Many Photons Does a 100 W Bulb Emit Per Second?

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SUMMARY

A 100 W incandescent bulb emits approximately 2.5 x 1020 photons per second of visible light at a wavelength of 500 nm. However, due to the bulb's efficiency, which is around 4%, the actual light energy output is about 4 W, resulting in an emission of approximately 1018 photons per second. The confusion arises from whether the 100 W refers to electrical energy consumption or light energy output. Understanding the efficiency of incandescent bulbs is crucial for accurate photon emission calculations.

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  • Understanding of photon energy calculations
  • Knowledge of incandescent bulb efficiency
  • Familiarity with the concept of wavelength in the electromagnetic spectrum
  • Basic principles of energy conversion in electrical devices
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  • Research the efficiency ratings of different types of light bulbs, including LED and CFL
  • Learn about the formula for calculating photon emission based on energy output
  • Explore the relationship between wavelength and photon energy using the equation E = hc/λ
  • Investigate the impact of bulb design on light output and efficiency
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Physics students, electrical engineers, and anyone interested in understanding light emission from incandescent bulbs and the principles of energy efficiency.

Brammo
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Estimate how many photons of visible light (500 nm) are emitted by a 100 W Bulb.

I get 2.5\times10^{20} Photons/Second

Am I correct?

Thank you.

EDIT: Added units.
 
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Two questions:

(1) Do you mean 2.5*10^20 photons/second?

(2) Does a 100W bulb emit 100W of light energy, or does it use 100W of electrical energy (or both)?
 
(1) yes, sorry. (2) I assume it means 100w of light energy. But what would the answer be if it was electrical?
 
It doesn't mean 100W of light energy. An incandescent bulb is only about 4% efficient, and so only puts out about 4W of light energy.
 
Ok well these are practice questions written by a physics professor. The answer he has written at the bottom of the questions is approximately 10^20 photons/second. I just wanted to know where i had gone wrong if I had. The question is as above and its not something you need to pick apart I was just asking for a little bit of help is all. It does mean 100W of light energy. So am I correct or am I incorrect? The idea is for us to learn and understand the formula.

Substituting in the value of 4W give you 10^18 photons/second which is much further out.
 
Brammo said:
Ok well these are practice questions written by a physics professor.

Then please post this in the appropriate section.
 

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