Purpose of Visible Light Properties field?

[Daithi]

Hi all,

Can I ask the purpose of the Visible Light Properties field in the Constructions Database dialogue box for glazed constructions? I have looked for guidance in the Construction Database user guide but found no reference to it.

I have defined three glazing types (single - 6mm float, double - 6:16:6 argon filled, and triple - 6:12:6:12:6 argon filled, and the value for visible light properties is returned as the same in each (0.76 or 76%).

I assume it's describing visible light transmittance...is that correct? If so surely it should display values similar to 0.88, 0.79 and 0.70 respectively (I sourced these figures from the Pilkington Spectrum online tool (http://www.pilkington.com/spectrum2/def ... ry_code=GB) using Optifloat for the glazing).

I note the field is editable by the user. But to what end? What does it affect during an Apache thermal simulation?

Sorry if these questions are basic, and appear to lead nowhere. I'm looking at both solar energy transmittance and visible light transmittance in relation to various glazing options and I'm trying to get to grips with what IES can do in each module.

Regards,

David.

[PCully]

Hi,

Visible Light Normal Transmittance is used by FlucsDL when measuring how much daylight is coming through a window.

It is user editable and so not directly reflated to the other values input on a glazed construction which describe the window properties with regards to solar energy.

Phil

[Daithi]

Thanks a million Phil, that's answered my questions!

[KasperS]

As i can see it (and from what you say) Radiance does not use this value, but uses the value in the "color map" thing. Why do you not use this value instead? It would make it a lot easier for people with different types of windows in the buildings? like when you have windows with a LT of 0.5 in the south facing rooms and 0.73 in the windows facing the other directions.

From Kasper

[PCully]

Hi Kasper,

there are a few areas of VE that don't use the properties defined in the CDB where intuition would suggest that it does. This is something we are focusing on this year and we are currently making improvements to CDB that you should see fairly soon that will make it easier to integrate all of the applications together.

The biggest discrepancy is the data used and defined by the thermal/energy apps doesn't always transfer to the Lighting areas and you will occasionally find these have their own inputs. Bit of a pain but as long as you know where and when the data is used (training and user guides should tel you this) then you can explain the results you are seeing.

Phil