IES-VE User Forum

Hello

I have been comparing Radiance with another program provided by Velux to see how close those 2 were, because the daylight factor given by radiance seems too low.

I have tried both with "Image > Illuminance - working plane" and "Right to light". Both of those says the DF is very low in the back of the room, around 0.3-0.4 while the velux program says it is around 2 %.
http://imageshack.us/photo/my-images/405/unledhn.png/

Anyone have an idea what im doing the wrong way with radiance since the difference is so large? I have changed inner surfaces to white and floor to wood color.

From Kasper

Hi,

I don't know all the details and haven't used Velux before but there may be assumptions made by either software which are then fed in Radiance resulting in the change of results, then there is also the question of making sure the model is defined the same in each program so that all the user inputs match.

Just another thought would be the version of Radiance used by each as I believe there have been some updates to Radiance since the last version that was integrated to VE (we're looking to upgrade just now)

Phil

Hello

I have also been comparing to some books about daylight in buildings, and those are very close to velux, but when comparing to deep inside the building they differ a lot from radiance. At one point i was thinking that Radiance only takes the Sky composition into account, and doesnt take into account the light reflected inside the room, because the books says that the reflected light inside a 6 m deep room is around 2 % DF itself, and therefore the 0.4 % that radiance calculates is impossible to get, and the graph of the DF from radiance looks a lot similar to a graph of just the SC.

Also found this in the help menu when clicking help after the calculation has been done. On page 9 of 19 it says: Units DF/SC switches units to daylight factor or Sky component.