When you are designing industrial lighting solutions, especially high mast systems, windage is something you simply cannot afford to overlook. It plays a crucial role in structural stability, safety and long term performance.
So what exactly is windage, and why does it matter so much in lighting design?
The word windage can mean different things depending on the context. In ballistics, for example, it refers to adjusting a projectile’s path to compensate for wind.
In engineering, however, windage describes how much of an object is exposed to wind and therefore how much pressure the wind can exert on it.
To make that easier to picture, think about walking outside on a windy day. When the wind pushes against you, that pressure is known as drag or drag force.
If you walk directly into the wind, you feel more resistance than if you turn sideways. The wind speed has not changed, but the surface area you are exposing to it has. That exposed surface area is effectively your windage. Increase the wind speed or increase the exposed area and the drag force increases too. Increase it enough and you could quite literally be knocked off your feet.
Now imagine a tall mast carrying multiple floodlights in an exposed environment such as an airport apron, port or stadium.
The last thing you want is for that structure to sway excessively or, in extreme cases, fail. Engineers must carefully consider windage when designing masts and mounting systems to ensure they remain stable under expected wind loads.
It is not just the mast itself that matters. The size, shape, positioning and weight of each luminaire all contribute to the overall drag force. Even small changes in geometry or arrangement can have a meaningful impact on the total load acting on the structure.
That is why windage is a key consideration at the design stage, not something to assess afterwards.
In practice, engineers focus less on calculating windage as a standalone value and more on calculating the drag force it contributes to. It is the drag force that ultimately affects structural safety.
The drag force is calculated using the following formula:
DRAG= ½ X V2 X ρ X EPA
Where:
V – is the air velocity.
ρ – is the air density.
EPA – is the Effective Projected Area.
EPA stands for Effective Projected Area. It represents the surface area of an object as “seen” by the wind, adjusted to account for its aerodynamic properties.
EPA is calculated as:
EPA = Cd × FPA
Where:
Cd is the drag coefficient
FPA is the Frontal Projected Area
To simplify this, imagine a rectangular box. Each side has a different surface area. The area directly facing the wind is its Frontal Projected Area, or FPA. The larger the FPA, the greater the potential drag.
When designing for safety, engineers typically consider the largest possible FPA as a worst case scenario.
However, shape matters too.
Now imagine a ball and a flat-ended cylinder of the same diameter. If wind hits them head on, they have the same FPA. But the ball is more aerodynamic, so it experiences less drag. That difference is captured by the drag coefficient, Cd.
By multiplying Cd and FPA, we arrive at EPA, which reflects both the size and the aerodynamic behaviour of the object. EPA is therefore a more accurate measure of how the wind will actually affect the structure.
For floodlight manufacturers, aerodynamics are not just theoretical. Products are typically characterised with a maximum EPA value listed under windage in the datasheet. This represents a worst case scenario to support structural calculations for masts and brackets.
When upgrading or installing lighting on high masts, understanding EPA is essential to ensure the existing structure can safely handle the additional load. It is a critical part of responsible engineering and long term reliability.
Windage may not be the most glamorous topic in lighting design, but it is one of the most important when it comes to keeping installations safe, compliant and standing exactly where they should be.