# the reference illuminance?

hi, all,

The tested illuminance value of the indoor point in the evening is 20 lux, but
the simulated value is 0.0 lux, so how to adjust the calculated value to 20
lux?

thank you.

ZZ

The tested illuminance value of the indoor point in the evening is 20 lux, but
the simulated value is 0.0 lux, so how to adjust the calculated value to 20
lux?

I do not know the parameters you used, but 0,0,0 means that most
probably you have no ambient calculation. As most parts of your room
will receive only indirect illumination, this will result in zero. Try
setting -ab to 2. To understand the effect of -ab for your scene, render
images of your room using -ab 0, -ab 1, -ab 2, -ab 3 with -av set to 0 0
0 for all renderings. You should see only a bright splotch of (direct)
sunlight for -ab 0, and increasing luminances for the areas receiving
reflected light with higher -ab bounces. Try it!

Also make sure to measure illuminance slighty OVER the plane - if you
are INSIDE geometry we all do not know what you will get for illuminance...

CU Lars.

Hi, Lars,

I’m trying to carry out thermal integrated daylighting simulation with ESP-r software. the first step is to verify if the tested illuminance of test point is in agreement with illuminance calculated by Radiance. If agreementis good, then I will use ESP-r coupling Radiance. that is why I pay attention to the illuminance of certain points.

And I haveperformed 7 days simulation with 1 hour timestep, which means I got 168 illuminance numbers of one test point. I find calculated illuminances of 6days is basically close to themeasured data. But1 day is exceptional, there is a big difference betweencalculated illuminances and meaured ones. That1 dayisa very clear sky because that day has a highest direct and diffuse radiation in those 7days, but the measured illuminance is much lower than other six day s. Anybody can tell why? and how to modifiy?

Thank you for your time.

ZZ

Thetestedilluminancevalueoftheindoorpointintheeveningis20lux,but
lux?

Idonotknowtheparametersyouused,but0,0,0meansthatmost
probablyyouhavenoambientcalculation.Asmostpartsofyourroom
setting-abto2.Tounderstandtheeffectof-abforyourscene,render
imagesofyourroomusing-ab0,-ab1,-ab2,-ab3with-avsetto00
0forallrenderin gs.Youshouldseeonlyabrightsplotchof(direct)
sunlightfor-ab0,andincreasingluminancesfortheareasreceiving
reflectedlightwithhigher-abbounces.Tryit!

AlsomakesuretomeasureilluminanceslightyOVERtheplane-ifyou
areINSIDEgeometrywealldonotknowwhatyouwillgetforilluminance…

CULars.

···

[email protected]

Hi,

it has been a while since I started radiance from inside esp-r. Can you
find out how to set the ab-parameter for the simulation? It is the
number of ambient bounces. I would set it to 3 in your case. Others
might suggest even higher values - you should increase it until there is
no real change observed any more.

CU Lars.

Hi, Lars,

Is ab-parameterset in the *.rif file?

ZZ

Hi,

findouthowtosettheab-parameterforthesimulation?Itisthe
numberofambientbounces.Iwouldsetitto3inyourcase.Others
mightsuggestevenhighervalues-youshouldincreaseituntilthereis
norealchangeobservedanymore.

CULars.

···

[email protected]

Is ab-parameterset in the *.rif file?

Yes, there should be a line INDIRECT, and there you can set something
like 3.

CU Lars.

hi, Lars,

My MSN is [email protected]

thank you.

ZZ

Isab-parametersetinthe*.riffile?

Yes,thereshouldbealineINDIRECT,andthereyoucansetsomething
like3.

CULars.

···