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Choosing the right lighting components
 
Several lighting devices (bulbs and luminaires) can be utilized to build the lighting system you have planned.  Once again, you should let the economizing principle be your guide.  Choose devices with the highest energy efficiency and durability possible. These components will not only provide improved quality of lighting but also protect the night environment.


1. Choosing the right bulb

Certain types of bulbs consume more energy than others with the same light output. You should therefore choose bulbs with a high lamp efficacy.

The table below shows a classification of the different types of light bulbs available with respect to lamp efficacy.

 
Classification of the main types of bulbs according to lamp efficacy.


The table below demonstrates the relationship between input power and luminous flux for these bulbs.

 
Relationship between input power and luminous flux for the main types of bulbs.


Different types of light bulbs emit different intensities of wavelengths. Spectrometers are used to measure the proportions of each colour of light emitted and results are presented as graphs showing the intensity of each colour. These graphs are known as light spectra.

The most polluting light sources in terms of sky glow are those that emit a lot of blue light. This is the case for white lights. White light is actually composed of all colours of the rainbow. Because the human eye perceives blue light less well than yellow light, a light source must contain a high proportion of blue light to appear white. It is the whiteness of light that permits a faithful colour rendering. Unfortunately, the bulbs that offer the best colour rendering are also those that pollute the most! This is why the use of these types of bulbs is sometimes prohibited on the IDSR territory.

 
2. Choosing the right luminaire

There exists a vast choice in outdoor luminaires, both functional and decorative, that have been designed for particular applications:

  • extensive areas, such as roadways, shopping centres and parking lots;
  • building facades and surroundings, such as entrances and parking spots;
  • loading and handling zones;
  • residential areas;
  • road or path markers.

Whatever the application, remember that light emitted towards the sky does not improve nocturnal vision but represents waste and pollution. Opt for luminaires that direct a minimal amount of luminous flux above the horizon.

Always choose luminaires with a high efficiency. Luminaire efficiency is the ratio of the luminous flux of a luminaire to the luminous flux of the bulb, expressed as a percentage. However, don't forget that only some of the light produced by a luminaire falls on the ground, since the rest is either lost in space or as heat. Take, for example, a wall sconce having an efficiency of 60% and a bulb of 6,000 lm. If 15% of the luminous flux is directed upwards, then 45% of the flux is directed downwards. Thus, of the 6,000 lm originally emitted by the bulb, 3,600 lm leave the luminaire and only 2,700 lm are actually available for lighting the ground.

The table below shows typical efficiency levels of luminaires that direct minimal amounts of luminous flux to the sky.

 
Typical efficiencies of luminaires that direct minimal amounts of luminous flux to the sky.


Aim the light where it is needed most. Choose luminaires according to their photometric characteristics, i.e., how the luminaire controls the luminous flux produced by the lamp.

For roadways, select luminaires that emit a minimum of light on the house side of the road and a maximum along the street side (see the figure below). The photometric report supplied by the manufacturer describes the distribution of luminous flux around the luminaire. Use this report to choose luminaires that fit your requirements.

 

A good roadway luminaire should emit a minimum of light on the house side of the road and a maximum along the street side. The description of the distribution of the luminous flux in the different back-light and forward-light zones is consistent with the new IESNA TM-50 classification.



Finally, you can save money by choosing luminaires that are both easy to maintain and equipped with high-performance parts. Make sure luminaires are composed of durable materials. Ovoid polycarbonate and acrylic lenses and opt for tempered glass. Also, check that the sealing is tight and conforms to the IP65 specification.

Demystification of the IESNA classification system

The design of a luminaire determines how the light will be emitted into the environment. Since designs vary widely, the distribution pattern of luminous flux around the luminaire can also vary greatly.

The IESNA has proposed a classification of luminaires according to their “cutoff class”. This system primarily depends on the amount of light emitted in the potential glare zone (in the 10° angle below the horizon). There are four categories:

  • non cutoff
  • semi cutoff
  • cutoff
  • full cutoff

Since this classification can not be used to define the exact proportion of luminous flux emitted above the horizon, only the “full cutoff” class guarantees that absolutely no light output is directed to the sky. Hence this system is often used incorrectly to simply limit the choice of a luminaire to one that does not light up the sky. It is important to realize that a luminaire in another class could emit less than 1% of luminous flux towards the sky while offering improved downwards efficiency. That is why the regulations adopted in the region of Mt. Megantic are based on a limit of 1% light emitted above the horizon (not just on the IESNA class). These by-laws thus allow for more options in high-performance luminaires. Don't forget that the photometric report contains all the pertinent data!

The IESNA first proposed the above four classes in 1963. In the last decade, however, light pollution (particularly light trespass and glare) became a real problem in most communities. Complaints were skyrocketing and new descriptions were required to clarify luminaire characteristics.

The IESNA thus revised its categories in 2007 to allow a more precise evaluation of the distribution pattern of light output. A brief article on the new classification system appeared in the July 2007 issue of the magazine Électricité Québec.