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Luminance, Illuminance and Concrete Pavement

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Luminance, Illuminance and Concrete Pavement PFB 1 - Luminance, Illuminance and Concrete Pavement It is widely accepted within our industry that a con- related to illuminance, factoring in the reflectivity of the crete parking area can lower lighting costs due to its surface. For a lambertian (uniformly reflective) surface, lighter color and higher surface reflectivity. However, it luminance is calculated using the equation L = (E / π) x ρ is not often that we see designers take advantage of this where L equals luminance, E equals illuminance and ρ opportunity. While it is important that an interior light- equals reflectivity of the surface. Luminance should not be ing system provide enough light for the individuals who confused with brightness, which is strictly a subjective es- live or work within the space, it is just as important that timate. exterior lighting be as effective to provide adequate visi- Several aspects of the lighting fixture, or luminaire are bility. Improper or poor exterior lighting can be a safety taken into consideration when designing for exterior light- hazard. Perhaps a better understanding of the lighting ing. Type of lamp, reflector, height of pole and number of industry and its needs can “shed some light” on the topic fixtures per pole all play a role in determining required and allow the concrete promoter to better assist lighting luminaires for a given area. A single luminaire has one engineers with their design process. light fixture per pole, a dual luminaire, two There are several terms that are essential in a discus- fixtures, and a quad luminaire has four fixtures. sion of lighting. Lumen is the unit used to indicate the Most lamps used in exterior lighting can be grouped as total amount of light given off by a single light source. High Intensity Discharge (HID) lamps. HID lamps pro- Candela is the basic unit for measuring luminous inten- duce light by means of an electric arc between tungsten sity from a light source in a particular direction. As electrodes that are housed in a gas and metal salt filled tube a point of reference, a common candle emits light with or globe. There are four distinct types of HID lamps: mer- a luminous intensity of roughly one candela. In the past, cury vapor, metal halide, high-pressure sodium (HPS) and candela was also known as “candle” or “candlepower.” low-pressure sodium (LPS). Each of these lamp types has Understanding the next two terms, illuminance and its preferred application, with HPS and metal halide being luminance, is critical to interpreting lighting design. An used most untrained person may use these terms interchangeably frequently but, in fact, they have distinctly different meanings. for land- In simplest terms, illuminance is the amount of scape, se- actual light that strikes a surface. The density of the illu- curity, minance is measured in lux (lumens per square meter, roadway abbreviated lx) or foot-candles (lumens per square foot, and parking abbreviated fc), and is directly related to the proximity area light- of the light source to the surface. The foot-candle is a ing. Both non-SI* unit of measure and is mainly used only in the HPS and United States, particularly in construction-related engi- metal hal- neering and in building codes. For purposes of conver- ide lamps sion, one foot-candle equals 10.764 lux. Illuminance have good should not be confused with illumination, which is de- Concrete’s high reflectivity allows owners to take efficacy, fined as the deliberate application of light to achieve advantage of greater luminance, with increased with ratings some aesthetic or practical effect. safety and reduced energy consumption. of 80 to Luminance is the light that is reflected by a surface, 130 lumens or transmitted through it, in the direction of the observer. per watt, and average life expectancy for both is between Measured in candelas per square meter (cd/m2) or 25,000 and 30,000 hours. HPS lamps were once the most candelas per square foot (cd/ft2), luminance is directly widely used lamp for exterior lighting, but more recently *SI refers to the International System of Units, commonly known as the modern metric system. The abbreviation SI comes from the French le Système international d'unités. have been replaced by the metal halide type, due to its life. In other conventional gas discharge lamps, the elec- wide wattage range (20W - 2000W) , slightly better effi- trodes are the part with the shortest life, limiting the lamp cacy, and more natural color rendition. lifespan severely. Since an induction lamp has no elec- The newest technology in lighting, the Light Emitting trodes, it can have a very long service life. In fact, service Diode (LED) is now making its mark in exterior light- life for an induction lamp can be as long as 100,000 ing. LED’s hours. That is equal to 11.4 years of continuous (24/7) provide illumi- operation or 25 years if operated 10 hours per day. Induc- nance equiva- tion lamps have been used since 1990 and their track re- lent to HID cord supports this claim. lamps but at a Another popular feature of the induction lamp is its fraction of the energy efficiency. Studies have shown that an induction energy con- lamp will use approximately 50% less wattage than either sumption. Sev- HPS or metal halide lights to produce the same lumens. eral LED Combining the lower wattage required for operation with manufacturers the long lifespan, an induction lamp emits less than half boast as much of the CO2 of an HPS or metal halide light. as 80% sav- With sustainability as the driving force behind devel- Light Emitting Diode (LED) lighting is now ings on elec- opment, there have been several recent legislative becoming more popular for exterior lighting due to the potential energy savings. tricity by using actions that require reductions in energy consumption to LED street be incorporated in new design and construction. For lighting. And estimates from the Department of Energy example, Executive Order #13423, Strengthening claim that adoption of LED’s for downlighting, street- Federal Environmental, Energy, and Transportation lights and other miscellaneous exterior lighting could Management (January 26, 2007) requires all federal remove twenty-two 1000MW coal burning power sta- agencies to reduce energy intensity by 30% by 2015. tions from the nation’s power grid. Theoretically, LED More recently, passage of the Energy Independence and life expectancy is greater than HID lights,, with claims Security Act of 2007 (EISA 2007) mandates specific of 80,000 to 100,000 hour lamp life, based on the reli- measures related to energy reduction that apply to all fed- ability of the diode. However, often the LED unit is not eral agencies. Among the new requirements for federal fitted with a high temperature integrated chip or other facilities are: means of heat dissipation and the LED may fail after as • 25% greater efficiency for light bulbs, to be phased in few as 10,000 hours. There is currently limited informa- from 2012 to 2014. tion regarding actual experience and most major LED • 200% greater efficiency for light bulbs, or similar suppliers are more conservative, with their estimates of energy savings, by 2020. life expectancy closer to 50,000 hours. Also a downside • All new and renovated federal buildings must imple- to LED lighting is that, while they consume considerably ment 55% reduction in fossil fuel use by 2010 and less energy than HID lamps, their efficacy is much 80% reduction by 2020. lower, as they produce as little as 25 to 45 lumens per • All new federal buildings must be carbon neutral by watt. 2030. Induction lamps are another newcomer to the exterior Many of the energy efficient lamps available today lighting market. The principle of the induction lamp can contribute to achieving these goals. When coupled dates back to the late 1800’s. Technological advance- with a concrete parking lot, the increased luminance can ments created a new interest in the early 1990’s. Induc- enhance their performance. tion lamps have seen wider acceptance over the past 15 Exterior Lighting Design years, and they are now getting a closer look because of their long lifespan and energy efficiency. Induction International lighting engineers calculate their require- lamps are similar to fluorescent lights in that they are ments based on both illuminance and luminance, taking gas filled and produce light as the excited gas emits UV the reflectivity of appropriate surfaces into consideration. radiation which is converted to white light by the phos- They look at the aesthetic, ergonomic and energy effi- phor coating on the inside of the bulb. However, unlike cient utilities of a lighting system and utilize the ambient the standard fluorescent lamp, induction lamps have no light provided by luminance to maximize those utilities. internal electrical connection and energy is transferred In the United States, however, recommendations for by electromagnetic induction. Also unlike conventional lighting are set by the Illuminating Engineering Society fluorescent lights, induction lamps are operable at tem- of North America (IESNA) and are based strictly on peratures as low as –40 degrees F. illuminance. Specific lighting levels are recommended One of the benefits of induction lights is their long for various applications. IESNA recommendations for to be 1.77 times higher than asphalt. Type of Area FC Armed with this information, lighting installations Primary Walkways - Commercial 0.9 - 2.0 for parking lots were evaluated, again comparing con- Secondary Walkways - Residential 0.2 - 0.5 crete and asphalt surfaces. Calculating a standard light- ing design for a 5,000 m2 parking lot with single and Major Streets (Arterial) quad 400 watt luminaires and a mounted pole height of Commercial 1.2 - 1.7 10 m, a total of 22 luminaires were required.
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