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Member
jemily
Posts: 4
Registered: ‎05-06-2009
Message 1 of 9 (699 Views)

Indirect Reflections and Daylight Factors

699 Views, 8 Replies
05-06-2009 02:22 AM
Hi all,

I seem to be having a problem calculating daylight factors using Radiance. I ran the daylight analysis for different scenarios varying the number of indirect reflections. I had anticipated the daylight factor should go up with an increased number of indirect reflections, but the results doesn't agree with this (see attachment)

Thank you,

Emily
Valued Contributor
yunpeng
Posts: 78
Registered: ‎08-09-2007
Message 2 of 9 (699 Views)

Re: Indirect Reflections and Daylight Factors

05-06-2009 08:15 AM in reply to: jemily
Do you talk about the parament "-ab(ambient bounce)"?
There is a limit for the number of -ab, after exceeding this limit, the change is not great. In some experiments, someone give the conclusion that the number is 5.
Attached image is a experiment about the relationship between DF and the number of -ab.
Member
jemily
Posts: 4
Registered: ‎05-06-2009
Message 3 of 9 (699 Views)

Re: Indirect Reflections and Daylight Factors

05-06-2009 08:39 AM in reply to: jemily
I'm assuming "-ab" is the same as indirect reflection - just out of curiosity where does that phrase come from? I wrote "indirect reflection" because that was the name given on the lighting analysis wizard, but if -ab is the technical phrase, sorry for any confusion!

Anyway, I thought that as the number of indirect reflection/-ab increases, the DF also increases - which is what your image is showing - but the results I gained from Ecotect are suggesting the opposite. On the attached excel spreadsheet, the general pattern is that the average DF decreases as the number of indirect reflection/-ab increases (aside from Scenario 2, where the DF increased for 8 -ab - why is this by the way?).

I hope what I'm asking is clearer now.

Thank you
Valued Contributor
yunpeng
Posts: 78
Registered: ‎08-09-2007
Message 4 of 9 (699 Views)

Re: Indirect Reflections and Daylight Factors

05-06-2009 05:30 PM in reply to: jemily
I can not open your excel(my office verson is 2003), you can upload your eco or rad files.
Member
jemily
Posts: 4
Registered: ‎05-06-2009
Message 5 of 9 (699 Views)

Re: Indirect Reflections and Daylight Factors

05-07-2009 01:40 AM in reply to: jemily
Hi, I've resaved the excel spreadsheet so it's compatible with the 2003 version, I hope it works. Thanks
Valued Contributor
yunpeng
Posts: 78
Registered: ‎08-09-2007
Message 6 of 9 (699 Views)

Re: Indirect Reflections and Daylight Factors

05-07-2009 07:56 AM in reply to: jemily
I have compare the daylight factor results, it is the same as you.
I think there is some thing wrong in ecotect`s daylight factor supposition.
To generate an overcast sky with a total horizontal illuminance value of 100 Lux, ECOTECT sets the -b parameter to 0.558659 (100/179, in fact it is also wrong, It should be: 9*100 / 7*179*PI) in gensky command. I think the key lies in this value is too small for actual conditions. If I change the -b value to 22(general conditions:10000lux) in gensky, the DF results will raise following the higher -ab number(that is right).
So I suggest you calculate the illumination, and then divide illumination by 20769.42 (this is illumination corresponding to the defauld -b 47.486034 ECOTECT set in gensky, I don't know why is this value) to get the DF.

Edited by: yunpeng on May 8, 2009 9:28 AM Edited by: yunpeng on May 8, 2009 9:35 AM
Member
jemily
Posts: 4
Registered: ‎05-06-2009
Message 7 of 9 (699 Views)

Re: Indirect Reflections and Daylight Factors

05-08-2009 02:30 AM in reply to: jemily
"So I suggest you calculate the illumination, and then divide illumination by 20769.42 (this is illumination corresponding to the defauld -b 47.486034 ECOTECT set in gensky, I don't know why is this value) to get the DF."

If I divide the illumination by 20769.42, the results would be far too small a number (i.e. in the 1x10^-3 region). Should I be dividing by 46.486034 instead?

Thank you
Valued Contributor
yunpeng
Posts: 78
Registered: ‎08-09-2007
Message 8 of 9 (699 Views)

Re: Indirect Reflections and Daylight Factors

05-08-2009 08:27 AM in reply to: jemily
1x10^-3 ? I do not encountered this phenomenon, I think you are using the DF calculation, you should get the illumination calculation, not the DF.
Attached image is the results I got.
Active Member
m.soderlund
Posts: 10
Registered: ‎09-30-2011
Message 9 of 9 (500 Views)

Re: Indirect Reflections and Daylight Factors

11-22-2011 07:02 AM in reply to: yunpeng

I would like to bring this subject up from it's grave because I'm having the same problem. More bounces gives lower results which is just plain wrong in my world. I can't really trust my results at the moment because they differ a lot depending on how many bounces I choose.

 

I tested with the solution provided, calculate as illuminance and it seems to work fine, the more bounces the higher the illuminance. But when I  divide by 20769 I get quite low DF results, a little bit too low in my opinion. Btw, the formula is in my version of Ecotect is  "V * 1,05", not "V * 100" as in yunpengs response, therefore I divided with 207,69 instead.

 

Does someone have a solution to this? Is the formula correct? 

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