Thursday, January 26, 2017

The OXL photometric file format, with spectrum, photos, and more...

The OXL file format is an XML based format which contains the photometry (like an IESNA .IES or an Eulumdat .LDT) file format, but adds much much more. The OXL file format is open and free to use by any company. Here's an overview of what an OXL file can contain:

As you can see there must be a photometry, and to that you can any or none of the following things:

  1. PDF data sheet.
  2. Photo.
  3. Spectral data.
  4. 3D model (a simplified 3D model is ideal for Revit applications).
So when a customer wants details about your luminaire, you don't need to send him N files, just a single OXL file.

Now I think examples are easier to understand than formal definitions, so here is what the start of an OXL file looks like:

Because Eulumdat and IESNA files are so constricted, some companies "expand and re-interpret" them, with non standard "extensions" which only a few programs (mostly company internal programs) understand. These extensions often force more data into the lines than they were designed for.

Eulumdata LDT has another restriction, it is only for CG (internal and road) photometries, and cannot hold VH (external floodlight) photometries.

OXL on the other hand is flexible and future proof. Since it is an XML format your programs/programmers/personel can ignore the branches it doesn't need and only pick out the data it wants. Also you can add your own special data which may be useful to your company, but can safely be ignored by extermal lighting programs.

Here is a link to an OXL photometric file which contains a photo and a spectrum.

Here is a link to 10 example OXL files in a single zip.

Here is the OxyTech web page which explains more about the OXL file format and here is a link to a (rather dated) OXL presentation.

But above all you should remember this image which illustrates what an OXL file can contain:

Wednesday, January 4, 2017

CIE88 2004, Calculation of Tunnel Lighting Transition Zone Length

This article is a bit of extra help for this one (on CIE88 2004).

We know that we need to arrive at an internal tunnel luminance Lin, and we know we start at the formula for calculating the curve is the one given above, Ltr. 

Time and distance are related by the fixed velocity, v, of the tunnel project. If we get the time taken to go through the transition zone we can easily get the length of the transition zone.

Re-arranging the original equation...

So you can calculate d, the length of the transition zone, from these three things:
  • the project velocity
  • the threshold luminance
  • the internal luminance.
(Thanks to Bui Duc Han for correcting an error in a previous version of the steps above.)

Comparisons of UNI11095 2003, CIE88 2004, UNI11095 2011 Tunnel Lighting standards

Here are the Luminance Grids for calculating Lseq. of all three standards:

In all three standards there are 9 rings and 12 (radial) sectors.

The UNI11095 2011 grid weights the upper and lower fractional sections by their reduced area. 

The CIE88 2004 has the "tallest" grid but the uppermost and lowermost areas are not used in the calculation, as they are considered to be outside a normal person's field of view. 

The UNI11095 2003 grid did not take into account the fact that the upper and lower areas are smaller, but it did have a wider aspect ratio.

UNI11095 2011 introduced a maximum curve above the minimum curve, presumably to encourage energy saving as well as luminous uniformity:

Tuesday, January 3, 2017

How To Calculate BUG Road Lighting Glare

Though BUG (IES TM-15-11, Addendum A) is quite hard to do, it is easy to understand, it gives you numbers for the "amount of light", wasted in various non-useful directions.
  • B stands for Backlight, light thrown back away from the road.
  • U stands for Uplight, light leaking skywards and causing light pollution.
  • G stands for Glare, how much light is wasted shining directly into (a relatively distant) the driver's eye.
The output of the luminaire is divided into several sub-zones:

Light issuing from High to Very High (H and VH) zones can cause glare from a distance and is anyway wasted light. These zones, both foward and back are used for the G rating. These are the red areas in the schematic below:

Light sent to the Back away from the road and towards the sidewalk (purple in the above diagram) is not useful for a car driver. This is sometimes called Trespass light. Back Low, Back Medium and Back High zones are used when calculating the B rating.

The blue areas in the image above (Upper Low and Upper High) show the zones where light is wasted skywards, allowing jet passengers to have a pretty view of the city below, but not much good to road users.

It is best to have most light in the Foward Low and Forward Medium zones, which shine light onto the road surface relatively close to the luminaire. These areas are green in the diagram above. FL and FM zones are not used in the calculation, they are not zones of wasted light.

So with the idea that it is a measure of waste, high numbers are considered bad, and low numbers are considered good:

A good mnemonic would be: "It BUGs me all this waste!".
Here is another example :

In the above example 13.7% of the light is wasted in the Uplight, hence the U5 rating. The B2 and G2 ratings are not brilliant either. 
When evaluating a BUG rating the BL and UL zones are not used, because these are considered to be useful light which shines down onto the road or sidewalk. The BL and UL zones in the above example are at the bottom of the circular diagram, from 30° to 30°.

Compare the above rating to this one:

Notice how no light is wasted into the sky, none is wasted shining light far away (the zones between 60° and 90° back and front). As a result the BUG rating is much better, B1 U1 G0.