9       Integrating lighting

In cooperation with AEE

9.1       General principles of lighting in common rooms

Common rooms, which are used as office space, should be illuminated with smooth and neutral coloured natural or artificial light. In order to provide adequate workstation, it is essential to avoid uncomfortable conditions caused through too low or too high luminance as well as high differences in light densities, flickering light, stroboscopic effects, direct and indirect lighting.

The European Standard EN 12464-1:2002 specifies lighting requirements for indoor working places which meet the needs for visual comfort and performance.

Public and office buildings often spend up to 50 % of their energy consumption on lighting. Since public buildings mainly are used during daytime, their energy consumption and cooling loads can be reduced through rational utilization of daylight. The substitution of artificial light with effective daylighting techniques can cause energy savings in the range of 35 to 75 %. In order to reach these energy savings the artificial lighting system must be energy efficient and controlled [SOB99].

 

9.2       Daylighting

Daylighting is the use of light from the sun and sky to complement or replace electric light. Appropriate fenestration and lighting controls are used to modulate daylight admittance and to reduce electric lighting, while meeting the occupants' lighting quality and quantity requirements [OCO97].

Many historic buildings already take advantage of a combination of daylight and artificial lighting. By using appropriate day lighting systems, large window openings of historic buildings can help to illuminate typical large, high rooms, where the daylight distribution rapidly falls off with distance from the window.

With the help of daylighting systems, sunlight can be led into the end of a room and create a smooth diffuse light distribution in the whole working area.

“Duo-curtain” daylight systems are very applicable for historic buildings, as they can be installed inside the building. They consist of mirrored deflecting blades divided in an upper and a lower part, which can be directed independently. For working stations it will be useful to adjust the lower part of the blades in the retro-reflection position, which means that incident solar radiation will be reflected, without causing glare or a heat transfer inside the room.  The upper part of the blades positioned horizontally create a deflection of the sunlight on the ceiling of the room, from where it can be further distributed into the room through a reflecting ceiling element. Duo-curtains can be located on the exterior or interior of any window, or between two panes of glass. 

Figures below show the effects caused by a window without a shading device in sunny weather. The result is a visually uncomfortable glare, important heat gains and consequently overheating the room. The implementation of the duo-curtain system is an effective measure against glare and overheating (retro-reflection position of blades in the lower part) and for the comfortable light distribution in the room (deflecting position of blades in the upper part).

Figure 84: Application and effect of “duo-curtain” day lighting systems (sunny weather) [POH07]

Figure 85: Practical implementation of the “duo-curtain” day lighting system [POH07]

 

9.3       Energy efficient artificial lighting

When the amount of daylight is insufficient for meeting the visual requirements of working places, adequate artificial lighting has to be applied. As mentioned above, up to 75 % of the costs for electricity can be saved through the implementation of an energy efficient lighting system.

“Light management” is the appliance of flexible and need-based lighting. In order to setup a light management system, several light fixtures must be controlled separately and the lighting must be able to operate in different switching and dimming states. These dynamic and energy efficient light management systems are controlled by “intelligent” electronic operation units that are integrated in light fixtures and operating elements. Electronic operation units can be installed for single light fixtures, for single rooms or building areas. A light management system, which can be a part of the building management system, controls and organizes the lighting system. It enables sporadic corrections according to individual needs without loosing its preset controls.  

Light management systems can easily be adjusted for new room layouts and partitions, while ensuring visual working conditions and low operating costs. These systems can adapt to various room layouts without any need for costly rewiring or reconfiguration and redundant downtimes. By defining room profiles, different lighting solutions can be implemented for different uses of the room.

With the help of a lighting control system, which regulates the lighting depending on the number of persons present or amount of incident daylight, considerable energy savings can be achieved because light is switched on only if needed. A control mechanism continuously compares the target and performance values of the lighting elements. It is however essential that a lighting control system does not disturb occupants, is reliable, conform to lighting standards and has a reasonable pay back period [IEA21].

There are various lighting control systems, which are controlled either centrally or locally. Locally controlled systems are used for single light fixtures. The local light sensors estimates the luminance of the working place and adjusts the light output of the light fixture to maintain a predefined level. Centrally controlled systems are used for whole buildings or building sectors. They use a single daylight sensor on the ceiling or the wall of a large area in the centre of a circuit.

Control systems with occupancy sensors helps to avoid that lighting is active when nobody is present in the room. After a specific time without movements, the lights will be switched off. As soon as a person enters the room, the light will be switched on. From a specific natural luminosity the attendance control is deactivated.

The luminosity dependent control regulates lighting systems by dimming or switching on/off with the help of light sensors. They measure the intensity of daylight or artificial light and if a specific threshold value is exceeded, the sensors give the signal to switch the lighting on or off or to dim the lighting up or down.

Daylight dependent control helps to compensate the varying intensity of daylight. Because of the variability of the daylight intensity, artificial lighting is essential, but not necessarily at full power. In order to achieve a constant lighting level, the artificial lighting may be dimmed, partly switched off or on.

The minimum luminous intensity required by standards normally leads to over-dimensioned lighting facilities, which leads to high energy consumption. Further maintenance factors like ageing of light sources, contamination of light fixtures, etc. must also be considered (Figure 86). The maintenance control system adjusts the lamp output according to its age and condition. This means that a constant level of lighting can be maintained across the whole lifetime of the light source, meeting the minimum requirements laid down in the standard while saving up to 20 % of energy compared with conventional facilities (Figure 87).

Figure 86: Without maintenance control: excessive light output with constantly high energy consumption (Zumtobel Licht GmbH)

Figure 87: With maintenance control: constant light output with reduced energy consumption [ZUM08]

Especially for retrofit measures it is recommended to install light fixtures with built-in sensors, where no extra control cabling is necessary. After the installation of the system, particularly in historic buildings, it may be necessary to make some adjustments because of pre-set installation settings based on assumptions on the average reflection factors, ceiling height, etc. of a typical office room.  Table 8 gives an overview of different lighting technologies.

Table 8: Key figures of different light sources [SOB99]

 

	Light source	Colour temper-ature (K)	Colour rendering (Ra)	Efficacy (lumen / watt)	Lifetime (hours)	Advantages	Disadvantages
	Incandescent lamps	2700	99	8-16	1000	Cheap Easy to install Good colour characteristics Light immediately Dimmable	High running costs Heat problems Short lifetime
	Fluorescent lamps	2700 – 7500	50-97	35-93	9000	Low running costs Different colours Low luminance	Flicker without HF ballast Need ballast and starter Light might seem “flat”
	Compact fluorescent lamps	2700-3000	83	20-80	8000	Small Low running costs Long lifetime	Different mountings Difficult to dim for small wattages
	Metal halide lamps	3000-6000	60-95	50-90	6000	Small High efficacy	Long lighting time Risk of colour differences
	High pressure sodium lamps	2000-2900	20-80	30-130	12000	Large wattages with high efficacy	Poor colour renderings
	LED lamps	3500 - 10000	- 65	- 30	40000 - 100000	Long lifetime No heat losses Small energy consumption	Light intensity decreases rapidly Expensive
	Daylight	6000-10000	~100	90-160		Varies during the day Free Very high efficacy	Varies during the day

9.4       References

[SOB99]          “Mid-Career Education: Solar Energy in European Office Buildings”, Technology Module 4: Daylight and Artificial Lighting, http://erg.ucd.ie/mid_career/mid_career.html, Project Report within the Altener program, 1999

[OCO97]         O’Connor J. Et al. “Tips for Daylighting with Windows – The integrated approach”, http://windows.lbl.gov/daylighting/designguide/designguide.html, accessed April 10, 2008

[POH07]          Pohl W. “Tageslichtnutzung in der Sanierung”, Presentation within the International Conference on high-quality rehabilitation of large volume buildings in Weiz (Ökosan 07), http://www.aee-intec.at/0uploads/dateien532.pdf, accessed March 25, 2008

[IEA21]            “Daylighting in Buildings – A source book on Daylighting Systems and Components”, A report of IEA SHC Task 21 / ECBCS Annex 29, http://www.iea-shc.org/task21, July 2000

[ZUM08]          Zumtobel Licht GmbH, www.zumtobel.be