Are you worried about the safety of tall pole lights in your outdoor settings? You need a standard measurement to make sure those high fixtures can withstand windy conditions. This is where you need EPA ratings.
Basically, the EPA rating is a form of analysis that is done to ensure that outdoor lights on high poles will remain stable against the wind. For example, the light fixtures need to meet the requirements of geographical areas such as coastal, lake, and mountain regions. For this reason, it is crucial to consider the EPA ratings while installing pole lights.
Today, I will elaborate on this technical topic for your better understanding.
What Is The EPA?
The full form of EPA is Effective Projected Area. This term measures the three-dimensional objects on a two-dimensional area. Also, it refers to the visible area of a three-dimensional shape against the wind at a particular angle.
For instance, the three-dimensional shape of a cone varies based on different angles. Sometimes it looks like a triangle, and sometimes it resembles a circle. As a matter of fact, all components of lighting, such as pole, fixture, and teno, will have separate EPA ratings. So, you will have to calculate the total EPA while setting up the lighting system.
What Is The EPA Wind Rating?
An EPA wind rating is the measured value of the maximum wind speed that a pole-mounted fixture can withstand safely. To elaborate, it calculates the total surface area of a fixture that a pole can support at a particular wind velocity. Through this value, you will get an idea of the structural integrity of your poles and fixtures against worst-case wind conditions. In the case of flood lights, the EPA measures the strength of a light pole.
For example, high wind zones such as Miami and Houston in America face 110 MPH (miles per hour) wind gusts. So, you will have to choose a light pole with an EPA rating that can handle 110 MPH wind conditions.
How Wind Affects Your Light Poles?
Wind causes first-mode or second-mode vibrations after striking a light pole. Sudden and high-velocity wind causes first-mode vibrations when it sways the pole’s top. However, this type of vibration is normally harmless, as light poles are flexible enough to handle the movement. In contrast, the second-mode or Aeolian vibrations are dangerous. Here, steady and low-velocity, high-frequency wind affects the middle of the pole. As a result, various issues such as cracked lamps, stress fractures, corrosion, and pole failure can occur in this situation. You need to use a vibration dampener to reduce this effect.
Importance Of EPA Rating
Preventing Dangerous Incidents
Pole-mounted fixtures should be capable of handling wind forces of an area. Considering the correct EPA rating ensures that the poles do not bend or knock over in the worst wind conditions.
Understanding The Wind Speed Requirements
You will need correct information about the wind conditions of different places before fixing light poles. EPA ratings help you understand the wind speed requirements.
Fixing The Installation Requirements
EPA ratings of the poles and light fixtures are required to understand what type of equipment you need for installing the lighting system.
How To Measure The EPA Rating?
1. Calculating the EPA of a Single Fixture
The formula of Effective Projected Area or EPA is as follows:
Effective Projected Area (EPA) = Projected Area (A) x Drag Coefficient (Cd) x Gust Factor
- Measurement of A: Project Area (PA) refers to the maximum cross-sectional area of a luminaire and its mounting when it is installed. The unit of this term is square feet.
- Measurement of Cd: Drag Factor (Cd) means how much resistance an object or shape can show in air. It is a dimensionless constant that is affected by air density, velocity, and frontal area. Air density should match the sea level conditions at 15°C. In addition, a higher drag coefficient means an object can resist the wind more. On the contrary, objects with a lower drag coefficient resist the wind less.
- Gust Factor: This factor refers to increased wind pressure due to gusting conditions. It is a dimensionless number provided in building codes or standards.
Example of Calculation: Suppose a light fixture has a frontal projected area of 0.158 square feet, a drag coefficient of 1.20, and a gust factor of 1. Then, its EPA will be 0.158* 1.20 * 1 = 0.190 square feet.
2. Calculating the Total EPA for a Light Pole Assembly
Here, you need the EPA of all the elements of the light pole assembly. So, use the following formula to calculate your light pole’s total EPA:
(EPA of light fixtures X quantity of light fixtures) + (EPA of the brackets X quantity of brackets) + (EPA of accessories X quantity of accessories)
Suppose the EPAs of two light fixtures are 5.2 square feet. One bracket has an EPA of 2.1 square feet, and one accessory has an EPA of 0.8 square feet.
The total EPA will be (5.2 * 2) + (2.1 * 1) + (0.8 * 1) = 13.3 square feet.
How To Buy A Light Pole Using the EPA Chart?
- Initially, find out the wind zone of the location where you will install lights from the wind speed map of your country.
- After that, measure the overall EPA of all the items mounted on the pole. You will find the EPA values on the specification sheets of the products.
- Now track down the maximum EPA for your wind zone on the chart.
- Make sure the total EPA of your equipment is within the maximum EPA allowed for that pole. Otherwise, you need to buy a better pole for the project.
How To Understand The EPA Requirements Of Your Project?
- First, decide on the location where you will establish the lighting system.
- Then calculate the EPA and overall weight of the pole assembly.
- After that, conduct a wind load analysis to determine the wind load requirement.
- Finally, take suggestions from pole manufacturers to verify the calculations and local conditions.
Factors Affecting The EPA Requirements Of A Light Pole
- Type and Number of Luminaires: Different light fixtures have different EPAs based on design, size, and shape. Also, a higher number of luminaires on a pole leads to more surface area that will be exposed to the wind. Thus, EPA requirements change with the type and number of luminaires.
- Weight of Light Fixtures: Light fixtures with heavy weights exert more force on their poles, influencing the pole’s wind rating.
- Mounting Brackets and Accessories: Mounting brackets for attaching the luminaire to the pole and other accessories increase the total surface area, drag coefficient, and, as a result, the EPA requirements of the pole.
- Pole Height: Pole height changes the calculation of the EPA requirement. For instance, taller poles will need stronger materials as they are more susceptible to wind.
- Pole Shape and Cross-Section: Different shapes of a pole represent different EPA ratings. In general, square poles will have higher EPA ratings than round poles. Besides, the diameter and wall thickness of the cross-section of the pole affect its load-bearing capacity.
- Material and Structural Design: The material used to manufacture the pole, such as steel or aluminum, and the structural design determine the pole’s capacity to withstand wind loads.
- Local Wind Conditions: You have to track the maximum wind speed of the local region before calculating the EPA values for a light pole. As a matter of fact, regions with a history of higher wind speeds will have lower EPA requirements. Therefore, you should select smaller fixtures, brackets, and accessories for a light pole in a high wind location.
- Installation Environment: The surrounding land, its exposure to wind, and the potential rate of vibration in the installation environment affect the EPA requirements of the light pole.
The Relationship Between EPA and AASHTO Guidelines
The American Association of State Highway and Transportation Officials (AASHTO) sets the AASHTO guidelines, which determine how EPA is used in designing outdoor lighting structures. The AASHTO guidelines help calculate wind loads on structures, which are directly utilized in the calculation of EPA. In this way, these standards help understand the structural requirements of light poles to withstand wind. In addition, they validate the EPA calculations in practical scenarios.
Frequently Asked Questions
The main purpose of the EPA rating in outdoor lighting is to understand the wind resistance of the fixtures. It will ensure the safety and stability of the lighting system.
The EPA value of a lighting product is normally found in the specification sheet or cutsheet provided by the manufacturer. They include EPA tables for every fixture.
Wind load refers to the wind force imposed on a light fixture. A 4000 Pascal wind load is equivalent to 180 MPH (miles per hour) or 290 KPH (kilometres per hour) wind speed against a structure.
Wind pressure values are collected throughout many years. That is why the American Society of Civil Engineers (ASCE) has made a wind speed map for the US. It helps identify wind pressure in a specific location. According to them, wind ratings normally fall between 70-110.
The ASCE 7-16 standard refers to the minimum requirements for determining design loads while building a structure. For example, it includes the calculation of different types of loads such as soil, flood, tsunami, rain, earthquake, wind, fire, and so on.
The Bottom Line
Understanding the EPA rating is necessary for installing outdoor pole lights. You have to make sure the total weight of the components mounted on the pole does not exceed its maximum EPA rating for that area. Otherwise, the safety and stability of the lighting system will be compromised.
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