Measure Light Intensity in Lux or Lumen with IMAQ Light meter in LabVIEW

[ericmatevosian]

Hi everyone!
I try to measure light intensity in Lux or Lumen in a machine vision project.
this is what I've done so far:

I grab the video from my webcam, and extract the Luminanc plane from the image and then wire it to IMAQ Light meter , which finally measure pixels Mean Intensity in the specified rectangle...

how can I convert this code to get me the Units Lumen or Lux ?

Thank you

Best Regards

Eric

 

[wwfeldman]

a lumen is a derived unit of luminous flux, or 1 lumen = 1 candela sr, where sr is steradian, a measure of solid angle
( a sphere is 4pi steradians)

a lux is a derived unit of luminous flux per unit area 1 lux = 1 lumen/m^2

check the specification of the measuring device to see what you get
that should help you process properly
what unit does the measuring device give you - that is, what are the units of the mean intensity?
probably an energy/area

 

[eric_s88]

a lumen is a derived unit of luminous flux, or 1 lumen = 1 candela sr, where sr is steradian, a measure of solid angle
( a sphere is 4pi steradians)

a lux is a derived unit of luminous flux per unit area 1 lux = 1 lumen/m^2

check the specification of the measuring device to see what you get
that should help you process properly
what unit does the measuring device give you - that is, what are the units of the mean intensity?
probably an energy/area

Hi wwfeldman , thank you for your reply and explanation.

the device I use is a camera which give me an image via LabVIEW IMAQ functions and then I measure the grayscale 8bit image pixels intensity which is a number between 0 to 255. the 0 represent full black, and 255 represent full white..

is there a way to measure light intensity in Lux or Lumen?

Best Regards
Eric

 

[luben111]

Hi, the mean intensity you get from the acquired image is correlated with the light intensity. Depend on the camera you use you can calculate the light intensity, ensure the camera auto exposure is turned off.

Getting the formula to calculate the light intensity in Lux or Lumens could be very sophisticated, I would suggest you take a light measuring unit and measure 10-20 different light levels. Make a table - camera reported average signal versus measured light intensity and store it in LabView. Then use LabView Interpolate 1D array VI to get the real time value.

 

[xjackal]

a processor may help.