questions about rendering using Radiance

[famous_doraemon]

I am using Radiance for measuring the working plane illuminance, however, there are some problems and hence i cannot continue with my work.

a) I have constructed a room and wanna compare the result between normal situation and using a mirror redirecting the sunlight into the room. obviously, the illuminance level in the deeper area of the room must be higher than that without a mirror. however, the result obtained is so depressed. seems like the result is worse than without a mirror. I don't know if I have set something wrong or not.

the sky is:
!gensky 7 29 15 -a 22.18 -o 114.08 -m 114.28 +s
the room is 6m x 4m x 3.2m
window is 4m x 1.9m on one of the smaller size of the wall.
mirror is adjusted to reflect the sunlight onto the deepest area of the ceiling.
value of -ab is 2
normally, the deepest area of the ceiling will have a higher illuminance level, however, the result is only the small, even slightly lower than without a mirror.

b) actually, how can i measure the working plan illuminance by using the Radiance? because i have tried so many times, and also read through Greg Ward's "Rending with Radiance", but still cannot find out the method to estimate the required result, but only the illuminance level of the wall, ceiling and wall. could anyone tell me about the process of evaluating the illuminance level of working plane (0.8m above floor)?

Really thanks a lot for those who could help me to solve this problem/read this message.

[Kevin]

What a great question!

Are you looking into this for general reasons of good lighting design? and/or, perhaps more specifically related to daylighting performance partinant to LEED certification?

Some thoughts:

Generally, it is not unusal to get somewhat confusing initial results of a new Radiance simulation, even for experienced users. This shouldn't be taken as discouraging, but simply as a natural part of using an extremely sophisticated state of the art tool, which is extending our cultural knowledge as we sue it, and for which the user interface trimmings are still being settled down.

More specifically, three kinds of things can easily throw off the result. First, imbalanced or inaccurate material properties will throw off the results. Second, imbalanced rendering paramaters can cause side effects that make results difficult to interpret (and for some reason, lighting effects from specular mirrors seem to be demanding of good settings). Third, it's surprising how often Radiance is literally giving the right answer (always in the absolute sense) but there is either a flaw in our common sense expectation about how the light would work, or a hidden condition in the model that leads to a different result.

I'm not saying this is your issue, in the least, but just to illustrate: Suppose there's reflection into the space from terrain or a ground plane. Then suppose that the sun angle chosen reflects light from the mirror so it misses the deep part of the room, which the mirror itself blocks diffuse reflections from the ground. In such a case - hard to catch looking deep into the room - the light there could be less with the mirror in place.

This is something our team is continuing to work on. Do others have specific experience with working plane illumination calcuations with Radiance?

[famous_doraemon]

really thx a lot for your reply~
actually i am a final year student who is doing a research about daylight utilization. I have read some of the research paper and wanna using the Radiance to simulate the result. but due to the problem faced in this stage, i cannot go any further....

You're right~ that's one of the reasons that causes a drop in illuminance level. Actually I doubt if Radiance can perform a good calcuatlion with reflection of daylight by mirrors.....
I think i need to spend more time on investigating it.... thanks for your comment!

and for the working plane illuminance, actually I discover a command called "dayfact". In Greg Ward's book, he has mentioned that:

"the dayfact script is a user-friendly interface to the illuminance prediction capabilities of rtrace. the script essentially performs the same rtrace illuminance calculation shown above, but in addition it can create contour plots of:
- workplane illuminance
- workplane daylight factors
- potential savings resulting from daylight illumination based on a given lighting design level"

but he hasn't mentioned much about how to use this script, and hence i cannot use this script for calculating the workplane illuminance level. is there any other script that can be used for workplane illuminance calculation? or is there anyone that knows how to use this script?

Thanks!

[seanm]

Hi

If you have Rendering with Radiance go to section 5.3 and read 5.3.1. If you need to understand falsecolor you can check out its man page directly or look at http://radsite.lbl.gov/radiance/man_html/falsecolor.1.html.

All else fails subscribe to http://www.radiance-online.org/ excellent Q&A sections used by people who wrote the software / book!

Sean