[Radiance-general] Measuring red, green and blue light component in certain space

[Axel Jacobs]

Adriana,
>
> To my knowledge, there is no standard metric for radiance independent
> of incoming direction.  You either need to define a particular
> direction, or in your case you probably want the irradiance value,
> which is the integral of radiance over the projected hemisphere.
> This also requires you to define a facing direction.

There is Joe Lynes et al. paper titled 'The flow of light into buildings'
(1966, IES Transactions), defining what he called 'vector illuminance'. It
has never really taken off big time, though...

The concept was implemented later on by Megatron in their 'CIM - Cubic
Illumination Meter', which to my knowledge is the only instrument of this
kind.
http://www.megatron.co.uk/homepage.html
The idea is to measure the light in the six main directions (+/-x, +/-y,
+/-z), thus defining a vector of illuminance.

The Advance RADIANCE Tutorial under
http://luminance.londonmet.ac.uk/learnix/docs.shtml, pp 43-...
will show you how to measure vector illuminance in RADIANCE (lots of shell
scripts). Since you're after the RGB, just separate the individual
channels.

Cheers

Axel