Converting Lux to Watt for Measuring Light Power

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SUMMARY

The discussion focuses on converting Lux measurements to Watts for a light source using a Lux meter. The user seeks clarification on the conversion process, which involves understanding the relationship between Lux, lumens, and Watts. The key method outlined includes dividing the Lux value by 6830 and then adjusting for the eye sensitivity coefficient based on the specific wavelength. The photopic efficacy at 560 nm is noted as 680 lm/W, which is crucial for accurate conversions.

PREREQUISITES
  • Understanding of Lux, lumens, and Watts
  • Knowledge of photopic efficacy and its application
  • Familiarity with wavelength-specific eye sensitivity coefficients
  • Experience with light measurement tools, specifically Lux meters
NEXT STEPS
  • Research the photopic efficacy values for different wavelengths
  • Learn about the conversion formulas between Lux, lumens, and Watts
  • Explore the use of Lux meters in various lighting conditions
  • Investigate the impact of different light sources on photopic efficacy
USEFUL FOR

This discussion is beneficial for optical engineers, lighting designers, and researchers involved in photometry and light measurement, particularly those converting Lux to Watts for precise applications.

yunusx
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Hi!
I need a little help. Here is my problem,
I have a light source and a monocromator that separates the white light to to its components of different wavelength. I want to measure the power of the output light which has a single wavelength. I am using a Lux meter to measure the illumation of the light but I don't know how to convert it into watt.

Could you please help me about this? ı am reading stuff about lux, watt and lumen but I am totally confused.
 
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Lux is lumens per square meter, where lumens in turn is a weighted function based on the photopic response of the human eye. To convert from lumens to watts (or watts to lumens) you need to use the photopic efficacy relation, which can be used to define lumens/watt as a function of wavelength.

I have an SPIE field guide which has a small table with discrete values for the photopic efficacy. For example, at a wavelength of 560 nm the photopic efficacy is 680 lm/w.

https://www.amazon.com/dp/0819452947/?tag=pfamazon01-20
 
Thanks for your help. :)
 
I have finally found a way of converting lux into watt. Just for being sure can you tell me whether its tru or not?
1- First i divide the the value of light illumation which i measured in Lux by 6830.
2- Then I divide the result i found by the eye sensivity coefficient which is different for each wavelength.
The result gives me mW/per sequare cm. Do you think there is a wrong operation?
 

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