Luminaire Selection

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General Performance Criteria

Fig.1  Placing corner luminaire on the bisector symmetrical light scallops are formed
Fig.2  Different appearance due to direct light only (left) or diffuse (right)

Luminaire selection should not be based solely on their efficiency since some additional issues have to be considered emphasizing comfort and ambiance. Thus selection criteria should include:

  • Luminance distribution on the surfaces. Harsh shadows, non-alignment with architectural details, disturbing scallops should be avoided. (see Figure 1)
  • Illuminance distribution on the working surface. Sufficient light levels to perform the task are needed with necessary uniformity ratios.
  • Visual comfort. Direct or reflected should have to be avoided by proper selection of luminaire photometric properties. Flicker should minimized as well.
  • Appearance of luminaires. Aesthetic integration with building interior image
  • Modeling. Enhancing 3d appearance of objects using a combination of direct and diffuse lighting. (see Figure 2)
  • Efficiency including possible use of sensors to reduce operation time or emitted light flux.
  • Maintenance easiness with relocation abilities when task position changes are expected

On top of the above mentioned criteria all luminaires should comply with a set of standards regarding safety requirements. Thus all luminaires can classified to different categories according to:

  1. Luminus flux distribution
  2. Protection against solid objects, liquids and mechanical impact (the last one is usually omitted) also known as IP rating.
  3. Degree of flammability
  4. Electrical protection
Section Key Resources
  • Advanced Lighting Guidelines, New Buildings Institute Inc, 2003
  • Rüdiger Ganslandt, Harald Hofmann, “Handbook of Lighting Design”, Vieweg Publ. , ERCO edition
Links
  • No links specific to this section have been listed.

Lead Author(s): Aris Tsangrassoulis

Photometric Data

Fig.1 

Selecting luminaires can be a tedious process with the designer trying to find the optimum solution combining desired light levels and distribution, glare reduction, energy efficiency and cost. Luminaire's photometric report is used to shorten this process by narrowing possible choices. Key characteristic is a graph presenting luminaire's intensity distribution (photometric curve, polar intensity curve) in cd/klm permitting direct comparison of various types of luminaires even if different lamp wattages have been used. For simplicity usually only longitudinal and transverse distributions are presented on a 2D graph (see Figure 1). The shape of the curve can help the design to select a narrow or a wide beam luminaire. High intensity values in angles between 0-30 degrees can cause veiling glare while above 60 direct glare issues might arise

Other diagrams that can be presented in photometric reports are:

Fig.2  Illuminance Cone Diagram
  • Cartesian, instead of polars, especially for floodlights since the represent more efficiently beam characteristics.
  • Illuminance cone diagrams for presenting spotlight maximum illuminance in relation to distance together with the beam diameter. The latter is defined according to beam's angle at which light intensity is 50% of the peak intensity. (see Figure 2)
  • Isolux diagram with the distribution of illuminance on a reference plane and specific luminaire mounting position

Other photometric data are:

  • Utilization factors denoting light flux percentage that reaches working plane. Manufacturers provide these factors for various combinations of room indexes and surface reflectances.
  • Luminaire's Maintenance factors
  • Maximum spacing to height ratio for both transverse and axial directions
  • Luminaire's efficiency
  • Glare metrics
Section Key Resources
Links

Lead Author(s): Aris Tsangrassoulis

Cost Strategies

Cost effective building is probably easiest to tell than to design it. Firstly because there are various interpretations of “cost-effectiveness” and secondly because building industry is guided mainly by “minimum initial cost” approach.

Among various alternative solutions concerning lighting schemes which are equal in terms of efficiency and initial cost , the more cost-effective is the one that has the lower life-cycle cost. Thus a proper economic method based on life-cycle cost analysis can offer comparison of the possible solutions based upon net present value. Although the method is solid it is often quite difficult to estimate accurately real costs or in many cases, where quality issues are involved , perks cannot weighted promptly.

For example an underestimation of some costs may lead the design team to a solution that cannot characterized as cost-effective. Such costs are in relation to:

  • Specific constructions due to seismic protection
  • Asbestos false ceiling
  • Necessary wiring
  • Prior upgrade of the lighting system

Among benefits, HVAC savings should be estimated in detail as well as any possible impact in productivity. During the initial phase of the selection activity simple economic performance measures such as Payback Period or Return Of Investment can be used. If the lighting investment under examination has negative ROI or there are alternatives with higher values of ROI then this investment should not be undertaken.


Section Key Resources
  • Economics for energy effective lighting for offices, DOE FEMP
Links

Lead Author(s): Aris Tsangrassoulis

Maintenance & Durability

Lighting system’s maintenance should be performed with easiness and simplicity and this should be taken into account during the initial design phase. That affect not only luminaire selection but their placement as well since use of excessive scaffolding to replace a small number of lamps is not cost-effective. Problems in minor components such as sockets and/or wiring might cause problems due to corrosion and the difficulty that might cause during regular service actions (e.g. relamping). Lack of maintenance can have a serious impact on lighting quality affecting peoples productivity in office environment. The best method to maintain proper light levels and designed uniformity is a maintenance schedule which will prevent light loss due to:

  • Lamp lumen depreciation
  • Lamp and ballast failures. Lamp failure rate is related to lamp operating time between starts, ballast type and installation. Ballasts have larger life expectancy than lamps but this can reduced significantly if there is an increase in operating temperature.
  • Dirt accumulation on lamps and luminaires
  • Reduction of room surfaces’ reflection factors due to dirt.

All the above mentioned parameters should be carefully predicted in order a proper maintenance strategy to be developed. For large installations group relamping usually occurs at 70% of lamp’s rated life matching the costs with budget allocation a year before.

Durability depends on the materials used for luminaire construction. See 5.3.4 for more information on degradation of luminaire properties due to corrosive environments. Cleaning should be performed with products that don’t deteriorate luminaire’s parts or cause secondary effects like development of static electricity in plastics (which in turn increases dirt accumulation).

Section Key Resources
  • Lighting Maintenance , EPA 430-B-95-009, January 1995
  • IESNA Lighting Handbook, 2000
Links
  • No links specific to this section have been listed.

Lead Author(s): Aris Tsangrassoulis

Manufacturing Waste & Disposal Issues

During the production line of a modern luminaire there are waste material that have to be handled with caution. The same applies when a lighting system has reached the end of service life and need to be disposed. Many light sources contain hazardous materials and these may be harmful to both environment and man if an improper waste management strategy is followed.

Toxic substances that is possible to be found in a luminaire are:

  • Toxic solvents in housing paints
  • Polychlorinated biphenyls (PCB) containing ballasts
  • Mercury and lead in discharge lamps (fluorescent, metal halide, mercury vapor etc)

Recycling is the proper environmental method to treat lighting waste. There are specialized organizations for this task. Another important fact is the waste caused by luminaire packaging. Cardboard packaging and cornstartch foam pellets can be recycled easily.

Section Key Resources
  • Lighting Waste Disposal, EPA 430-B-95-004, September 1998
  • Advanced Lighting Guidelines, New Buildings Institute , 2003
Links
  • No links specific to this section have been listed.

Lead Author(s): Aris Tsangrassoulis

Page Key Resources
  • No publications general to this page have been listed.
Links
  • No links general to this page have been listed.
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