[Radiance-general] Ximage illuminance readings

[Greg Ward]

Dear Steve,

The 'l' command in ximage applies the 179 lumens/watt conversion  
factor, so if the input is a picture created by rpict with the -i  
option, you should be seeing lux values on your opaque surfaces.  If  
you are off by a factor of ten, then I would suspect the input values  
or the calculation are at fault.

Best,
-Greg

> From: steve michel <smichel_designer at hotmail.com>
> Date: March 10, 2008 10:48:33 AM PDT
>
> I know this is supposed to be fairly basic but needs clarification:  
> I want to get lux readings from my pic files
> When generating *.pic files (with -i option for irradiance) ,  
> viewing them with ximage and
> selecting a point with the ximage 'l' command gives me values that  
> are clearly NOT lux values (values appear to be 1/10th of my  
> expected lux measurement).
> Correct me if I'm wrong, but isn't the value in W/m2 at an efficacy  
> of 179lm/watt? For daylight only or all irradiances? If so, what  
> conversion to get lux values?
>
>
> regards
> Steve