# Number of emitted photons per second

• Coldslooks
In summary, the average wavelength of an LED is 500nm and it emits 300mW of electrical power with an efficiency of 66%. To calculate the number of emitted photons per unit time, the energy of one photon can be multiplied by the overall energy transformed into light, which is equal to 300mJ times 66%. This yields a result of 5x10^17 photons per second.

## Homework Statement

The average wavelength that LED emits is 500nm. The electrical power of the LED is 300mW and the efficiency of turning energy into light is 66%. Number of emitted photons in unit time is?

## Homework Equations

##E_f=hcf##
##\frac{Pt}{E_f}=number of photons##

## The Attempt at a Solution

After calculating the energy of one photon i am to find the overall energy that is transformed into light. The energy is ##300x10^{-3}J## but how am i to include the efficiency? Just multiply the Energy with 0.66 and use that in the equation? The answer is suppose to yield ##5x10^{17} per second##

Coldslooks said:

## Homework Equations

##E_f=hcf##
First, this must make no sense. The correct one should be ##E=hf.##
Since you can get the energy of a photon, then given the amount of light you can calculate the number of the photons. Like what you said, the energy transferred to light per second is ##300mJ\cdot 66\%.##

Coldslooks
tommyxu3 said:
First, this must make no sense. The correct one should be ##E=hf.##
Since you can get the energy of a photon, then given the amount of light you can calculate the number of the photons. Like what you said, the energy transferred to light per second is ##300mJ\cdot 66\%.##
Yeah, your right, i haven't seen that I've put ##c## there, thanks.
Well then, ##\frac{E_t}{E_f}=\frac{198*10^{-3}J}{hf}##
##f=\frac{c}{w}=6*10^{14}## yes the rest is clear thanks :)

## 1. What is the "number of emitted photons per second"?

The number of emitted photons per second, also known as photon emission rate, is a measure of the total number of photons that are emitted from a source within a one-second time interval. It is typically denoted as N and is expressed in units of photons per second (photons/s).

## 2. How is the number of emitted photons per second calculated?

The number of emitted photons per second can be calculated by multiplying the photon emission rate (N) by the area (A) of the surface from which the photons are being emitted. This can be represented by the equation N = I x A, where I is the photon intensity (in units of photons per unit area per unit time).

## 3. What factors can affect the number of emitted photons per second?

The number of emitted photons per second can be affected by various factors such as the energy level of the emitting source, the material and physical properties of the source, and external factors like temperature and pressure. Additionally, the number of emitted photons per second can also be affected by the distance between the source and the point of measurement.

## 4. How is the number of emitted photons per second measured?

The number of emitted photons per second can be measured using specialized equipment such as a photodetector or a spectrometer. These devices can detect and measure the number of photons emitted from a source within a given time interval, allowing for the calculation of the photon emission rate.

## 5. Why is the number of emitted photons per second important in scientific research?

The number of emitted photons per second is an important measure in scientific research as it provides information about the properties and behavior of light-emitting sources. This information can be used in various fields such as astronomy, physics, and chemistry to understand the nature of matter and energy, and to develop new technologies and applications.

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