Converting Lux to Watt for Measuring Light Power

  • Thread starter Thread starter yunusx
  • Start date Start date
  • Tags Tags
    Lux Watt
Click For Summary

Discussion Overview

The discussion revolves around the conversion of lux measurements to watts for a light source with a specific wavelength. Participants explore the relationship between lux, lumens, and watts, particularly in the context of using a lux meter and understanding photopic efficacy.

Discussion Character

  • Technical explanation
  • Mathematical reasoning
  • Homework-related

Main Points Raised

  • One participant seeks assistance in converting lux measurements to watts, expressing confusion about the relationships between lux, watt, and lumen.
  • Another participant explains that lux is defined as lumens per square meter and mentions the need for photopic efficacy to convert between lumens and watts, providing a specific efficacy value for a wavelength of 560 nm.
  • A later participant outlines a proposed method for conversion, involving dividing the lux value by 6830 and then by a wavelength-specific eye sensitivity coefficient, asking for validation of this approach.

Areas of Agreement / Disagreement

Participants do not appear to reach a consensus on the conversion method, as the last participant is seeking confirmation of their proposed calculations, indicating uncertainty in the process.

Contextual Notes

The discussion includes assumptions about the photopic efficacy values and their application across different wavelengths, which may not be universally applicable. The specific method proposed by the last participant has not been validated by others in the thread.

yunusx
Messages
10
Reaction score
0
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.
 
Engineering news on Phys.org
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?
 

Similar threads

Procedure to express radiation intensity of an LED in watts/cm^2
  • · Replies 6 ·
Replies
6
Views
2K
Radio Power Conversion: Convert mV/m or nW/m2 to Watts
  • · Replies 4 ·
Replies
4
Views
2K
Undergrad Lux-meter, candelas or lux, measuring nits in practice
  • · Replies 2 ·
Replies
2
Views
5K
Undergrad Calculating distance between lux meter and light source
  • · Replies 2 ·
Replies
2
Views
2K
Kill-a-watt meter -- What does it measure?
  • · Replies 8 ·
Replies
8
Views
5K
High-Power LEDs -- Maximum 'Lumen-Density'?
  • · Replies 8 ·
Replies
8
Views
2K
Measuring Power output of DC generator
  • · Replies 38 ·
2
Replies
38
Views
6K
High School Converting Lux to W/m^2 for Solar Radiation Measurement
  • · Replies 9 ·
Replies
9
Views
11K
Selective Incident Headlight Intensity Measurement
  • · Replies 3 ·
Replies
3
Views
2K
Undergrad How can I convert lux to watts for CFL bulbs?
  • · Replies 2 ·
Replies
2
Views
2K