EPA of Lighting Fixture

[Illuminator]

I am being asked to specify the EPA (effective projected area) of one of our lighting fixtures. How is this calculated?
Is it:
a) Merely the cross sectional area of the fixture normal to the wind direction.
b) The cross sectional area times a coefficient that accounts for the shape of the fixture. What are the specifics for calculating the coefficient?

Does wind speed and altitude above the ground come into consideration when supplying a EPA figure?

Thanks in advance,
Gabriel

 

[JAE]

I believe that it is b).

AASHTO has a document that deals with the design of highway luminaires using EPA. Basically, the shape of the luminaire affects the way the wind drags on the object. This is taken up by a factor that is applied to the area (i.e. 1.3 for example).

The designers then can determine the wind speed, and resulting wind pressures and apply those pressures directly to the object's EPA and get the wind force applied to the object.

 

[JAE]

Here's the actual publication:

BR-LTS-4-M Standard Specifications for Structural Supports for Highway Signs,Luminaires and Traffic Signals, 4th Edition and 2002 Interim

Here's the website:

https://www.transportation.org/publications/bookstore.nsf

do a search for "luminaires" and you'll find it.

 

[Illuminator]

Thank you JAE for the information. Although I have not been able to purchase the BR-LTS-4-M standard, looking up AASHTO and luminaires has led me to some examples on the web.

The examples state:
EPA=(frontal projected area) * (drag coefficient of the luminaire)

The drag coefficient is found by wind tunnel analysis. Since I don't have access to a wind tunnel, I will assume worst case scenerio of a flat plate with a coefficient of 1.2.