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Light Distribution

Luminaire luminous flux can be directed upwards and/or downwards reaching working surface directly or indirectly. According to the percentage of the light flux that directed above or below the horizontal the following classification scheme is applied:

Type Upward flux Downward flux Comments
Direct 0-10% 90-100% Most efficient accompanied by possible shadows, glare
Direct luminaire.jpg
Type Upward flux Downward flux Comments
Semi-direct 10-40% 60-90%
Semi-direct luminaire.jpg
Type Upward flux Downward flux Comments
General diffuse 40-60% 40-60% Flux equally distributed to all directions
Type Upward flux Downward flux Comments
Direct-indirect 40-60% 40-60% Equal upward and downward fluxes
Direct-indirect luminaire.jpg
Type Upward flux Downward flux Comments
Semi-indirect 60-90% 10-40%
Semi-indirect luminaire.jpg
Type Upward flux Downward flux Comments
Indirect 90-100% 0-10% Reduced efficiency, elimination of veiling reflections
Indirect luminaire.jpg
Section Key Resources
  • European Norm 13032-1:2004: Light and lighting. Measurement and presentation of photometric data of lamps and luminaires. Measurement and file format.
  • IES LM-75-01:Goniophotometer Types and Photometric Coordinates
  • IES LM-66-00:Electrical and Photometric Measurements of Single-Ended Compact Fluorescent Lamps
  • IES LM-9-99:Electric and Photometric Measurements of Fluorescent Lamps
  • No links specific to this section have been listed.

Lead Author(s): Aris Tsangrassoulis

Luminaire Efficiency and Effectiveness

It is defined as the ratio of light flux (lumens) emitted by luminaire to that of the lamps in it. It value is depended on the optical design of the reflector , the properties of the diffuser (if any) the number of lamps and their relative position.

The maximum value of LE is 1 (or 100%) , but that doesn't necessarily mean that this value represents the best choice since bare lamps can achieve this value causing at the same time severe glare problems. Another definition of LE is the Light Output Ratio (LOR) which can be split up in Downward and Upward LOR. This parameter is usually found at the bottom right hand corner of the photometric diagram. Typical value for direct type luminaires with linear fluorescent lamps is ~ 0.6 while values more than 0.8 can achieved. In order to take into account effects from all luminaire components a new metric has been introduced. Luminaire Efficacy Rating (LER) is the ratio between light output to input power (lm/W):

LER=[Luminaire Efficiency * Total Rated Lamp Lumens * Ballast Factor ]/[ Luminaire power input ]

According to Energy Policy Act of 2005, during the selection process of fluorescent luminaires, Federal Agencies should confront with lumianire performance requirements table.

Performance requirements
Luminaire Type Number of lamps Required LER (instant-start) Required LER (programmed-start)
2'x4' Recessed
Lensed 2 >74 >69
3 >71 >68
4 >68 >63
VDT-preferred Louvered 2 >61 >56
3 >60 >57
4 >601 >57
Comparison of two different lighting schemes.

Section Key Resources
  • No links specific to this section have been listed.

Lead Author(s): Aris Tsangrassoulis

Appearance and Architectural Integration

Hybrid luminaire with light guide components (

Lighting systems are fundamental to the building environment. It is apparent that a successful design aims at achieving pleasantness, which in turn is due to the integration of the luminaires into the architecture of the space. What the observer sees might neither be what the space designer aims at nor what the lighting consultant intends to present.There is always a mutual interaction of space and light capable to stimulate mood. This emotional impact is always related to the brightness contrast and this is precisely what a proper lighting design aims to together with the provision of sufficient light levels on the working surface.

For reasons of perception (interpretation simplicity), the lighting system is often in concordance with the architectural elements to avoid confusing patterns. During the initial design phase there are three tasks that have to be accomplished:

  • Provision of sufficient light on the task area
  • Provision of ambient lighting
  • Creation of visual interest

Flynn’s work suggested that there are three cues to determine user’s reactions to a lighting situation:

  • Uniform/not uniform distribution
  • Bright/dim levels and c)overhead/peripheral lighting. The adjustment of these can have an impact on the users subjective response.

The purpose of the design might be the concealment of the luminaires (e.g.recessed) in falseceilings, coves etc. or make them visible . In the latter case, both the luminaire's scale in relation to architecture and the design details of the luminaires are of great significance as they can refer back to a specific historical period.

The integration of the luminaires can negatively affect the acoustics of a space, either due to the noise that they themselves make (e.g. old technology ballasts) or it can affect the transmission of sounds due to their plastic cover for example.

Because of the existence of other HVAC components in false ceilings, the layout of the recessed luminaires should be in accordance with them as well.

Section Key Resources
  • Gary R. Steffy, “Architectural Lighting Design”,John Wiley and Sons Ltd, 2001
  • Advanced Lighting Guidelines, New Buildings Institute Inc, 2003
  • Lou Michel , “Light: The Shape of Space: Designing with Space and Light”, Publ. Wiley, 1995.
  • Gary Gordon “Interior Lighting for Designers”, Wiley Publ., 2003
  • Flynn, J.” A Study of Subjective Responses to Low Energy and Nonuniform Lighting Systems”, Lighting Design and Applications, 7(2), 1977

Lead Author(s): Aris Tsangrassoulis

Definition of Advanced Luminaires

By definition advanced luminaires incorporate innovative characteristics which separate them from conventional ones. Such characteristics are:

  • Efficient combination of lamps – ballasts
  • Efficient optical design by using proper reflector shape

Cut-off device from Bartenbach LichtLabor, Austria, for Osram PowerTOPLED, right. aspherical optics from Fraen, Italy, for Luxeon Emitter

  • Glare reduction using especially designed refractors, keeping light sources away from direct view.
  • Ability to control light flux through the use of light/occupancy sensors and thus reducing energy consumption.

Independent luminaire daylight dimming system

  • Ability to either modify mechanically light distribution by moving lamp in relation to the reflector
  • Ability to modify CCT during operation

Change of lamps CCT in relation to time

  • Satisfaction of multiple application alternatives

Section Key Resources

Lead Author(s): Aris Tsangrassoulis

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