Enter the frequency, the number of photons, incident area, and time into the calculator to determine the light intensity.
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Light Intensity Formula
The following formula is used to calculate the intensity of light shining on an area.
I = [n*f*h] / [ A * t ]
- Where I is the light intensity (candela, cd)
- n is the number of photons
- h is Planck’s constant
- f is the frequency
- A is the incident area
- t is the time
Light Intensity Definition
Light intensity, or luminous intensity as it’s often referred to as is a measure of the power emitted by a light source in a certain direction.
This light emission is both wavelength-weighted and per unit of solid angle. Light intensity is studied in the field of photometry.
Example Problem
How to calculate light intensity?
- First, determine the number of photons being emitted.
For this example, to be simple, the number of photons emitted in the specific direction is found to be 2,000.
- Next, determine the frequency of the light.
For this problem, the frequency is calculated to be 40 m^-1
- Next, determine the incident area.
The total area the light is hitting is found to be 50m^2.
- Next, determine the change in time.
The light emission is measured for 10 seconds.
- Finally, calculate the light intensity using the formula above.
I = [n*f*h] / [ A * t ] = [2,000*40*(6.62607004 × 10-34 ] / [50*10] = 1.0601712e-31 Candelas (cd).
FAQ
What units are light intensity measured in?
Light intensity (luminous intensity), is measured using the units candela which is abbreviated (cd)
