Table of Contents:
What is light?
Basic parameters used in lighting
Quality characteristics of lighting
On quality characteristics
Measuring illuminance
Types of lighting
Lighting concepts
Humanergy Balance
Comprehensive assessment of lighting quality (ELI)
Calculation of energy efficiency (LENI)
Warning: The content of this article is cited from The Lighting Handbook by ZUMTOBEL
What is light?
Light is that part of the electromagnetic spectrum that is perceived by our eyes. The wavelength range is between 380 and 780 nm.
What does the human eye see?
Light has a triple effect
Light for visual functions:
Illumination of task area in conformity with relevant standards
Glare-free and convenient
Light creating biological effects:
Supporting people’s circadian rhythm
Stimulating or relaxing
Light for emotional perception:
Lighting enhancing architecture
Creating scenes and effects
Basic parameters used in lighting
Luminous flux – Luminous intensity – Illuminance – Luminance
Ω = solid angle into which luminous flux is emitted A = area hit by luminous flux AL · cos = visible areas of light source ρ = reflectance of area pi = 3.14 * = for diffuse surface areas
Luminous flux: The luminous flux describes the quantityof light emitted by a light source.The luminous efficiency is the ratio ofthe luminous flux to the electrical powerconsumed (lm/W). It is a measure of a lightsource’s economic efficiency.
Luminous intensity: The luminous intensity describes thequantity of light that is radiated in a particulardirection.This is a useful measurement for directivelighting elements such as reflectors. It isrepresented by the luminous intensitydistributioncurve (LDC).
Illuminance: Illuminance describes the quantity of luminousflux falling on a surface. It decreasesby the square of the distance (inversesquare law). Relevant standards specifythe required illuminance (e.g. EN 12464“Lighting of indoor workplaces”).
Luminance: Luminance is the only basic lighting parameterthat is perceived by the eye.It specifies the brightness of a surface andis essentially dependent on its reflectance(finish and colour).
Quality characteristics of lighting
The right light – traditional and new quality criteria
Traditional quality criteria:
Glare limitation
Good modelling
Correct light colour
Avoidance of reflections
Harmonious brightness distribution
Sufficient illumination level
Appropriate colour rendering
New quality criteria:
Changing lighting situations
Personal control
Energy efficiency
Daylight integration
Light as an interior design element
Illuminance – definition of terminology
Illuminance maintenance value Ēm: value below which the illuminance level must not fall in the visual task area.
Visual task area: illuminance levels are specified for specific visual tasks and are designed for the area in which these may take place. If the exact location is unknown, the roomas a whole or a defined area of the workstationis used for specification.The visual task area may be a horizontal,vertical or inclined plane.
Area immediately surrounding the visual task area: here illuminance may be one level lower than in the visual task area (e.g. 300 lx to 500 lx).
Maintenance factor: the initial value multiplied by the maintenance factor gives the illuminance maintenance value. The maintenance factor can be determined individually, and takes the installation’s reduction in luminous flux caused by soiling and ageing of lamps, luminaires and room surfaces into account.
The maintenance schedule (the cleaning and maintenance intervals for the lamps and installation) must be documented.
On quality characteristics
European Standard EN 12464 regulates the lighting of indoor workplaces. In doing so, the unified glare rating method is used to evaluate (psychological) glare.
UGR is based on a glare formula. This formula takes account of all the luminaires in the system that contribute to the sensation of glare.
UGR levels for luminaires are determined using the tabular method according to CIE 117. Zumtobel also specifies the UGR index complied with by all luminaires concerned.
Reference values for specific room sizes are given in the data sheets.
UGR levels are available for each individual product in the corresponding photometric data sheet.
Example: www.zumtobel.com/42178787 (Photometry tab)
UGR limits (UGRL) that must not be exceeded:
≤ 16 Technical drawing ≤ 19 Reading, writing, training, meetings, computer-based work ≤ 22 Craft and light industries ≤ 25 Heavy industry ≤ 28 Railway platforms, foyers
The UGR limits are specified in the EN 12464 standard for activities and visual tasks
The UGR method takes account of the brightness of walls and ceilings (1) as well as all luminaires in the system that contribute to the sensation of glare (2). The result is a UGR index.
The luminance limiting curve method assesses the mean luminance between 45° and 85°, and formerly even the glare effect of a luminaire.
The new European standard sets UGR = 19 as the maximum permissible value for offices, which is equivalent to the luminance limiting curve for 500 lx in Quality class 1.
UGR values are available for each individual product in the corresponding photometric data sheet.
Example: www.zumtobel.com/42178787 (Photometry tab)
Illuminance levels on ceilings and walls
Unlit ceilings and walls create an unpleasant room impression. Bright surfaces, however, pleasantly enhance the room climate.
The EN 12464 standard therefore requires an illuminance level of at least 30 lx or 50 lx* on ceilings and at least 50 lx or 75 lx* on walls. In fact, these levels ought to be significantly exceeded and should be at least 175 lx on walls.
* in offices, class rooms, hospitals
Spatial illumination
In order to enhance people’s and objects’ recognisability in a room, basic requirements are placed on cylindrical illuminance ĒZ and modelling.
Hence, ĒZ should be as high as 150 lx in rooms used for communication.
Modelling is the ratio between cylindrical and horizontal illuminance at a specific point and should be between 0.3 and 0.6.
Light colour
The light colour describes the colour appearance of the light.
In addition to the colours of the surfaces, it is also the light colour that determines a room’s basic atmosphere!
Colour rendering
– = Banned or no longer recommended under EU Regulation 245/2009 (EUP), due to low efficiency and inappropriate colour rendering.
Measuring illuminance
The Mean illuminance is the arithmetic brilliance level measured with a lux meter in a defined grid, under precisely specified conditions.
Measuring instruments:
Description and precision:
L: maximum precision, tolerance 3 %
A: high precision, tolerance 5 %
B: average precision; tolerance 10 % (minimum requirement)
Measuring grid and measuring level: In order to facilitate inspection of the lighting system, the measuring grid has been specified in the EN 12464 (Lighting of workplaces) and EN 12193 (Lighting of sports facilities) standards.
Workplaces = 0.75 m; sports facilities (floor) = 0.03 m
Circulation areas, stairs, car parks (floor) = 0.03 m
Cylindrical illuminance = 1.2 m
Measuring grid: congruent triangles
Measuring grid not congruent with luminaire layout grid
Measuring conditions:
Avoid external light/daylight (measure separately and subtract)
Check mains voltage and ambient temperature
Use new, burnt-in lamps (discharge lamps 100 h)
Types of lighting
Direct lighting
Indirect lighting
Indirect/direct lighting
Mellow Light
Direct lighting:
Highly directional
Strong glare reduction at certain angles
Dark ceiling (cave effect)
Limited flexibility of workstation layout
Energy efficiency on the task level
Indirect lighting:
Diffuse lighting conditions
Room gains in height
Glare-free
Workstations can be positioned anywhere
Low energy efficiency
Indirect/direct lighting:
Pleasant room impression
High user acceptance
Good contrast ratios
Flexible workstation layout (indirect component > 60 %)
Mellow Light:
Recessed direct/indirect solution
Workstations can be positioned anywhere
Glare-free
Reduced luminance levels at all viewing angles
Gives impression of daylight in room
Lighting concepts
The definition of individual visual tasks for the purpose of lighting design in a room, as provided for in the EN 12464 standard, opens up new perspectives for lighting design. The quantity and quality of light can now be specified exactly for any task area.
Task area related lighting concepts are a customised tool to fully exploit the additional options provided. At the same time they offer financial scope that can be used to improve lighting comfort and enhance the effect of a room.
Visual function: Task area related lighting provides the right amount of light at the best possible quality for every visual task. Uniformity, control of glare and reflections, good contrast rendition and shadow detail are consistently matched to the respective task.
The lighting is adjusted perfectly to the room user’s needs.
Emotional and biological effects: Focusing the lighting onto clearly defined areas means saving investment and operating costs. The funds saved can be used to improve comfort and enhance the room atmosphere, for instance by exciting lighting accents, illuminated walls or dynamic lighting scenarios.
Optimum energy efficiency: Large buildings provide huge potential for optimisation of energy consumption. Lighting that is consistently focussed onto individual task areas reduces mean illuminance levels and therefore the average expenditure on energy. Savings can be further increased by using daylight-based lighting management and presence detectors.
Room-related lighting concepts take neither individual task areas nor different visual tasks into account. They are based on the most demanding task performed in the room. The position of the workstation is not defined, the entire room disposes of a uniform lighting quality.
Lighting focussed onto individual visual task areas provides for varied light design in the room. By illuminating walls, for instance, rooms can be designed to be much more open and attractive; dynamic lighting situations can enhance their visual quality.
Humanergy Balance
Human aspects + Energy efficiency = Humanergy Balance
The Humanergy Balance concept harmonises both aspects of lighting and makes it possible to assess them: ELI, the lighting quality indicator, takes their physical and psychological effects on people into account; LENI, the energy efficiency indicator, assesses the economic and ecological aspects of light.
Comprehensive assessment of lighting quality (ELI)
The Ergonomic Lighting Indicator (ELI) allows to assess lighting quality in terms of quantity, using five descriptive quality criteria.
Checklists are used to record the individual criteria, which are displayed in a Kiviat graph (spider chart). The outermost line in the graph indicates optimum fulfilment of a criterion.
Example of ELI assessment using a spider chart:
Calculation of energy efficiency (LENI)
The Lighting Energy Numeric Indicator (LENI) stands for a lighting installation’s actual energy consumption in kWh per square metre per year.
LENI is determined according to the specifications of the EN 15193 standard (assessment of buildings in terms of energy used – energy requirements made on lighting).
Formula for calculating a lighting installation’s energy consumption:
Without elaborating on individual parameters in greater detail, the following relevant factors are identified:
The installed load (Pn)
Multiplied by the annual hours of use by day (tD) and at night (tN)
Reduced by the factors (≤ 1) for daylightbased control (FD), presence-based control (FO) and a constant lighting control system (FC) (e.g. maintenance control)
The area assessed (A)
The following factors have a positive impact on the reduction of energy consumption:
Sensible control of lighting
Use of daylight
Use of presence detectors
Intelligent consideration of hours of use
Energy-efficient lamps
Need-based use of luminaires and lighting solutions, specified for the respective application
Constant lighting control (maintenance control)
Visual performance: Lighting in conformity with relevant standards is decisive for ensuring that a visual task can be identified and the related activities can be carried out. Consideration of the traditional quality characteristics of lighting has a major impact on visual task performance.
Lighting level
Uniformity of illuminance
Colour rendering
Avoiding hard shadows
Contrast rendition
Physiological glare
Vista: In prestigious buildings, for example, light is not only needed for seeing but also enhances the looks of the interior. Light can provide guidance and make people accept the interior on account of the first visual impression they get.
Architectural design
Mental design
Guidance
Hierarchy of perception
External appearance
Material
Luminaires’ protection type
Protection against harmful radiation
Visual comfort: Light is not only needed in the visual task area, but also for perception in the room. Rooms should be illuminated with uniform brightness and lighting balance.
Balanced brightness distribution
Varying luminance levels
Plasticity/modelling
Discomfort glare
Uniform illuminance in area aroun visual task
Sense of security
Artificial lighting complemented by daylight
Use of flicker-free ballasts
Vitality: Light significantly influences people’s activity and sense of wellbeing. Moreover, it has a positive impact on their health and may even enhance or influence biological processes.
Sense of well-being
Activation and stimulation
Circadian rhythm
Lighting similar to daylight
Avoiding danger spots
Avoiding thermal radiation
Electromagnetic fields
Empowerment: Varying visual requirements, visual tasks or periods of use call for options to individually influence one’s lighting situation. Sensors and control systems help users adjust the lighting situation to their personal needs.
Individual influence by switching and dimming
Choice of lighting scene
Presence detection
Daylight-based control
Choice of lighting scenarios
Flexibility for layout changes
Privacy
Reference: The Lighting Handbook by ZUMTOBEL
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