Calculate optical power output of LEDs

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SUMMARY

The discussion centers on calculating the optical power output of LEDs using a photodiode to measure photocurrent at various wavelengths. The formula employed is R (A/W) = I/P, where R is the responsivity of the photodiode, I is the measured photocurrent, and P is the optical power output. Users report obtaining unexpectedly low optical power values, such as 0.027 mW for a LED rated at 17000 mlm, raising concerns about the calculation method. The conversation suggests that an integral may be necessary instead of a simple summation for accurate results.

PREREQUISITES
  • Understanding of photodiode responsivity and its measurement
  • Familiarity with optical power calculations and relevant formulas
  • Knowledge of LED specifications, including luminous flux (mlm)
  • Basic principles of photometry and radiometry
NEXT STEPS
  • Research the use of integrals in optical power calculations for LEDs
  • Explore photodiode responsivity curves and their impact on measurements
  • Learn about the relationship between lumens and optical power output
  • Investigate calibration methods for photodiodes in optical measurements
USEFUL FOR

Engineers, optical scientists, and technicians involved in LED performance testing and optical power measurement will benefit from this discussion.

Sophie MC
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Hi guys,

I have to calculate de optical power output of a set of LEDs. For that I used a photodiode to measure the photocurrent at each wavelength and then calculate the optical power at each wavelength using the following formula:

R (A/W) = I/P,

where R is the responsivity of the photodiode at each wavelength,
I is the photocurrent measure with the photodiode at each wavelength and
P is the optical power output at each wavelength that I want to measure.

I have de responsivity curve of my photodiode and I have measure the photocurrent. However when calculating de optical power output I obtain very small values.

For example, for a LED with typical 17000 mlm (from datasheet), I only obtain 0,027 mW (summation of all wavelegths) of optical power. I think that this is a very small value comparing with the value in lumens (17000 mlm).

Can any on help with this? Am I right? Am I wrong? Is this the right way of calculate optical power?

Thank you so much
 
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We would have to see your raw data and your methods to comment.

Are you using a sum where an integral is needed?
 

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