I have modeled a cubical room (4 x 4 meters) with no windows or any type
of apertures; the room is completely closed and empty, without any kind of
objects inside. There is only a diffusive light source located in the
middle of the ceiling. My intention is to change the color and texture of
the walls, and then measure the resulting light reaching the geometrical
center of the room: 1)INTENSITY (in radiance units) and 2)the amount of
RED, GREEN and BLUE of the resulting light spectrum also in radiance
units. How can I do these measurements?
Adriana Lira
Master in Design Studies, 2003
Candidate for Doctor in Design Studies
Harvard Graduate School of Design
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.
Phil Dutre has a nice compendium that explains lighting units, which may be found at:
I have modeled a cubical room (4 x 4 meters) with no windows or any type
of apertures; the room is completely closed and empty, without any kind of
objects inside. There is only a diffusive light source located in the
middle of the ceiling. My intention is to change the color and texture of
the walls, and then measure the resulting light reaching the geometrical
center of the room: 1)INTENSITY (in radiance units) and 2)the amount of
RED, GREEN and BLUE of the resulting light spectrum also in radiance
units. How can I do these measurements?
Adriana Lira
Master in Design Studies, 2003
Candidate for Doctor in Design Studies
Harvard Graduate School of Design
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.