Area lighting Design Calculations - Part Two


In the previous article " Area lighting Design Calculations - Part One", I indicated that the most commonly used design methods for floodlighting calculations are:
  1. The point-by-point method, 
  2. The beam-lumen method, which include:
  • IES method, 
  • CIE method. 
  1. Isolux Diagram Method, 
  2. Computer Aided Design. 

And I explained the point-by-point method and the beam-lumen method as per IES.

Today, I will explain Second method – Part Two: Design Procedure for The beam-lumen method as per CIE method for Area (flood) lighting design as follows.

You can review the following previous article for more information and good following: 
Part Two: Design Procedure for The beam-lumen method as per CIE method


Introduction and definitions: 

IES: (Illuminating Engineering Society).

CIE: (International Commission on Illumination).

Light pollution:  is light with no “useful” purpose i.e. wasted energy. Inefficient light sources such as incandescent or mercury vapor lamps cause energy waste.

Light pollution includes the following (4) phenomena:

1- Glare




Simply, Glare is Intense and blinding light that causes discomfort and a reduction in one’s ability to see.

2- Light trespass




Light trespass is Light falling where it is not wanted or needed. Light trespass also is intrusive lighting. Spill light (also called stray light) is light falling outside of the intended area, which can result in light trespass. Light coming into a yard or bedroom window at night from streetlights, the nearby car dealer or mall, or from a neighbor’s security light is light trespass. This type of light pollution also has glare and wastes both light and energy.

3- Visual clutter and confusion

Light “noise” in the field of view that is both distracting and annoying. Examples might include too many brightly lit signs or too many bright lights. For example, visual clutter and confusion would make it difficult to see or differentiate between directional signs and traffic signals.

4- Artificial sky glow



The artificial brightening of the night sky due mostly to inefficient lighting fixtures that project light upward. Artificial sky glow is wasted light. It brightens the night sky often to such an extent that only the moon and a few of the brightest stars remain visible.


And to control the above (4) phenomena, many Lighting ordinances around the world (like IESAN, CIE, IDA, ..) provide a regulatory strategy provisions to control the quality and value of outdoor lighting by assigning recommended lighting zones for outdoor areas.


Design Steps for The beam-lumen method as per CIE method

Step- 1: Determine the dimensions of the area to be illuminated.

Step- 2: determine the type of lighting application.

Step- 3: determine the lighting zone type.
  • Lighting zones are based on the highly varied lighting needs within a city or region and are a key element in modern lighting ordinances. 
  • The zones recommended by the International Commission on Illumination (CIE) allow different amounts of light in areas with different nighttime characteristics. 
  • Lighting zones are defined based on the following factor: 
  1. ambient lighting levels, 
  2. population density, 
  3. other community considerations. 
  • A description of the lighting zones is provided in the CIE model ordinance which includes (4) lighting zones (E1, E2, E3 & E4) as in following table: 



To this list of Zones, IDA (International Dark-Sky Association) adds a fifth Lighting Zone (E1A) with ambient lighting level and description as in above table. 

The following luminaires and lighting systems are exempt from above lighting zones: 
a- Internally illuminated signs 

However, it is strongly encouraged that all such signs should have “dark” backgrounds (opaque or colored) and “light” lettering (white or lighter colored than the background) so as to minimize glare or luminous overload.

b- Externally illuminated signs
However, it is strongly encouraged that all such signs be lit from above, with fully shielded fixtures.

c- Temporary lighting for theatrical, television, and performance areas.

d- Lighting in swimming pools and other water features governed by Article 680 of the National Electrical Code.

e- Code-required exit signs.

f- Code-required lighting for stairs and ramps.

g- Temporary holiday lighting provided that individual lamps are 10 watts or less.

h- Lighting required and regulated by the Federal Aviation Administration, U.S. Coast Guard, or other federal or state agency.

i- Interior lighting.



Step- 4: Determine the Lamp Power Allowance

The maximum allowed Lamp Power Allowance shall be determined from the following table:




Notes to above table:
  • It applies to all outdoor lighting, whether attached to building, poles, structure, or self-supporting, including, but not limited to, hardscape areas (which include parking lots, lighting for building entrances, sales, and non-sales canopies), lighting for all outdoor sales areas, and lighting for building facades. 
  • If there is an energy code in place, then the more restrictive provisions of this ordinance and that energy code shall apply. 
  • Only one application type may be applied to any given area. 
  • Canopy allowances include only the area within the drip line area of the canopy. 


Step- 5: Determine the type of floodlights

we have 2 cases as follows:
  1. According to Use class and lamp lumen,
  2. According to Maximum lamp wattage.

Case#1: According to Use class and lamp lumen
All nonexempt outdoor lighting fixtures shall have shielding as shown in following Table:

 

Notes to above Table:
  • Flood or spot lamps must be aimed no higher than 45 degrees above straight down (half-way between straight down and straight to the side) when the source is visible from any off-site residential property or public roadway. 
  • All Class 3 lighting shall be extinguished between 11:00pm (or when the business closes, whichever is later) and sunrise. 
  • Residential refers to all residential land-use zoning, including all densities and types of housing such as single-family detached and duplexes. Multiple-family residential uses must use standards above for Class 1, 2 and 3 lighting. 
  • Any lamp installed on a residential property must be shielded such that the lamp itself is not directly visible from any other residential property. 


Case#2: According to Maximum lamp wattage
All nonexempt outdoor lighting fixtures shall have shielding as shown in following Table


Notes to above table:
  • All outdoor lighting shall comply with the limits to lamp wattage and the shielding requirements in above Table. 
  • Only luminaires that are allowed to be unshielded in above Table may employ flexible or adjustable mounting systems. All other luminaires shall be permanently installed so as to maintain the shielding requirements of above Table. 
  • All canopy lighting must be fully shielded. However, indirect “up-light” is permitted under an opaque canopy provided that no lamp or vertical element of a lens or diffuser is visible from beyond the canopy and such that no direct “up-light” is emitted beyond the opaque canopy. 

Step- 6: Determine the quantity of floodlights Lamps (N)

  • Calculate the total wattage for a given area by multiply the area (square footage) of each of the application types by the allowed lamp wattage per square foot for the appropriate lighting zone. 
  • Add up the total of the lamp wattage for each application type. 
  • Calculate the number of floodlights lamps (N) as follows: 
N = total of the lamp wattage / wattage of one lamp 



Step-7: Determine the Location of floodlights

As in previous topic 
Area lighting Design Calculations - Part One".



Step-8: Determine the Luminaire mounting height

We have two cases for the installation height of outdoor lighting fixtures as follows:
  1. Pole-mounted lighting. 
  2. Lights mounted to buildings or structures 

A- Pole-mounted lighting


Lighting mounted onto poles or any structures intended primarily for mounting of lighting shall not exceed a mounting height of 40 percent of the horizontal distance of the light pole from the property line, or a maximum height according to the following Table, whichever is lower.

Exceptions to above table: 

  • Exception one: Lighting for residential sports courts and pools shall not exceed 15 feet above court or pool deck surface. 
  • Exception two: Lights specifically for driveways, and then only at the intersection to the road providing access to the site, may be mounted at any distance relative to the property line, but may not exceed the mounting height listed in above Table. 
  • Exception three: Mounting heights greater than 40 percent of the horizontal distance to the property line but no greater than permitted by Table 3 may be used provided that the luminaire is side-shielded toward the property line. 
  • Exception four: Landscape lighting installed in a tree. 


B- Lights mounted to buildings or structures


Lighting mounted onto buildings or other structures shall not exceed a mounting height greater than four feet higher than the tallest part of the building or structure at the place where the lighting is installed, or higher than 40 percent of the horizontal distance of the light from the property line, whichever is less.


Exceptions:
  • Exception one: Lighting attached to single family residences shall not exceed the height of the eave. 
  • Exception two: Lighting for facades may be mounted at any height equal to, or less than the total height of the structure being illuminated regardless of horizontal distance to property line. 
  • Exception three: For buildings less than 40 feet to the property line, including canopies or overhangs onto the sidewalk or public right-of-way, luminaires may be mounted to the vertical facade or the underside of canopies at 16 feet or less. 


Step- 9: check the amount of total output light

The amount of permitted total outdoor light shall not exceed the limits in the following Table:



(The values in this table are upper limits and not design goals; design goals should be the lowest levels that meet the requirements of the task.)

Notes to above Table:
  • (1) This refers to all land-use zoning classifications for multiple family, commercial and industrial uses. 
  • (2) This refers to all residential land-use zoning classifications, including all densities and types of housing such as single-family detached and duplexes. 
  • In Lighting Zones E4-E1, each residential single-family detached home or duplex is allowed up to 5,500 total lumens (2,300 lumens in Zone E1A), or the amount indicated in this Table based on the parcel's acreage, whichever is larger. Each is also allowed a maximum of 5,500 lumens (zero lumens in Lighting Zone E1A) of unshielded ("A") lighting, provided Table in 2.A above allows the lamp's type with "A" shielding. All residential spot or flood lamps permitted are to be aimed no higher than 45 degrees above straight down (half-way between straight down and straight to the side). 


Step-10: determine the suitable Luminaire spacing


As in previous topic 
Area lighting Design Calculations - Part One".



Step-11: determine the suitable Aiming of Luminaires


As in previous topic 
Area lighting Design Calculations - Part One".




Third: Isolux Diagram Method

The number of floodlighting Towers / High masts required has to be determined first by the Isolux method using the Isolux diagram of luminaires to be used & follow the following steps:




Step-1: Convert the Isolux diagram also to the layout drg. scale and determine the diameter of circles which can be drawn covering the area so that the permissible spacing to height ratio is attained. 

Step-2: Trace the Isolux diagram of the luminaire on tracing paper and place the centre of Isolux diagram on the centre of each circle on the area to be illuminated. 

Step-3: Read the values of illumination levels at the centres of all grids from the Isolux diagram and prepare a table. 

Step-4: Determine the contribution of all lights to the illumination levels at the centre of each grid and enter the total values of the illumination levels in the table/grid diagram of the area. 


Notes:

This method is found to be less tedious and more accurate as compared to the lumen method or the point by point method.



In the next Article, I will explain Computer Aided Design programs for outdoor lighting design. Please keep following.




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