Visual Comfort & Lighting Quality
LIGHTING
Definition
Light
part of the electromagnetic spectrum
that is perceived by our eyes
wavelength: 380-780 nm
color effect
cones come on during the day
we see colors
rods come on during the night
we only see shades of grey
Human Centric Lighting
Definition
Triple effect
expresses the positive effect of light and lighting on the health, well being, and performance of humans
has short and long term benefits
visual functions
comfortable Illumination of task area
glare-free and convenient
emotional perception
lighting enhancing architecture
creating scenes and effects
creating biological effects
supporting people’s daily routine
stimulating or relaxing
Basic Parameters
Luminous flux
the quantity of light emitted by a light source
unit: lm (lumen)
luminous efficiency [lm/W]
measures for the light source's economic efficiency
Luminous intensity
the quantity of light that is radiated in a particular direction
unit: cd (candela) or lm/sr
luminous intensity distribution curve (LDC)
measures for directive lighting elements (e.g. reflectors)
Illuminance
the quantity of luminous flux falling on a surface
unit: lx (Lux) or lm/m2
Luminance
the only basic lighting parameter that is perceived by the eye
the amount of light reflected from or transmitted through a surface (brightness of an object)
unit: cd/m2
depends on a large extent on the degree of reflection
Quality Characteristics
Traditional quality criteria
sufficient illumination level
harmonious brightness distribution
glare limitation
avoidance of reflections
good modelling
correct light color
appropriate color rendering
New quality criteria
changing lighting situations
personal control
energy efficiency
daylight integration
light as an interior design element
terminologies
Illuminance maintenance value [Em]
illuminance level must not fall in the visual task area
Visual task area
illuminance levels are specified for specific visual tasks
If the exact location is unknown, the room as a whole is used for specification
plane: horizontal/vertical/inclined
Area immediately surrounding the visual task area
illuminance may be one level lower than in
the visual task area (e g 300-500 lx)
Maintenance factor
illuminance maintenance value = maintenance factor x initial value
takes the installation s reduction in luminous flux caused by soiling and ageing of lamps, luminaires and room surfaces into account
Uniformity
should not be any great differences in brightness so that uniformity should not fall below Emin/Eavg
Reflectance factors
not only the perception of the room but also the reflected light and thus the room’s brightness
the ratio of the total amount of radiation, as of light, reflected by a surface to the total amount of radiation incident on the surface
Glare
the difficulty of seeing in the presence of bright light (e.g. direct or reflected sunlight or artificial light)
types of glare
disability glare
reduces one's ability to see
types of disability glare
directly from a light source itself (luminaire [light fixture] or a window)
indirect (reflected off of some surface in the space)
discomfort glare
does not necessarily reduce one's ability to see (though it can) instead, it more resulting in discomfort
caused by luminance in the field of view that are high relative to the average luminance of the field of view
limitation
direct glare
cause
luminaires without glare control
very bright surfaces
effect
loss of concentration
more frequent mistakes
fatigue
remedy
luminaires with limited luminance levels
blinds on windows
reflected glare
cause
reflective surfaces
incorrect luminaire arrangement
incorrect Workstation position
effect
loss of concentration
more frequent mistakes
fatigue
remedy
matching luminaire to workstation (layout)
indirect lighting
matt surfaces
VISUAL COMFORT
Unified Glare Rating (UGR)
Introduction
standard for classroom: UGR<19
value: 40 (extremely high glare) to 5 (very low glare)
help control the risk that occupants of a building will
experience glare from artificial lighting
an objective measure of glare
Definition
an expression of the relative intensity of the light from a light fitting compared with the intensity of the light from the surrounding area, as perceived by the viewer
can only be calculated for an indoor lighting installation (not for exterior installation and for a light fitting on its own)
predicts the glare caused by an electric lighting system along a psychometric scale of discomfort
predicts the amount of discomfort causing glare produced by a lighting installation for a fixed set of conditions
discomfort glare can result in annoyance, headaches, or eyestrain
its different from disability glare, which impacts the viewer’s ability to recognize objects accurately
measure of discomfort glare, not disability glare
Recommendations to reduce UGR
increase a background luminance
decrease the luminance of the luminaire as seen by the viewer (narrow the beam angle or decrease the wattage)
angle the luminaires away from the viewer so they are not shining in their eyes
avoid positioning the fittings in the viewer's direct line of sight
Light Color
describes the color appearance of the light
the colors of the surfaces
determines a room s basic atmosphere
Light Rendering
ability of a light source to reproduce surface colors (8 test colors R1 to R8) as realistically as possible compared to a reference light source
Coloring Rendering Index (CRI)
value
best: Ra = 100
very good: Ra > 90
good: Ra > 80
Ra < 80
not recommended at workplaces
used in exceptional cases, it has to be ensured that safety colors can be recognized without any problems
The saturated test colors R9 to R14 are occasionally used to describe a light source's special functions
measurement
mean illuminance
the arithmetic brilliance level measured with a lux meter in a defined grid under precisely specified conditions
precisions
maximum precision (L): tolerance 3%
high precision (A): tolerance 5%
average precision (B): tolerance 10% (minimum requirement)
conditions
avoid external light/daylight (measure separately and subtract)
check mains voltage and ambient temperature
use new, burnt in lamps (discharge lamps 100 h)
grid
congruent triangles
not congruent with luminaire layout grid
levels on ceiling and wall
unlit ceilings and walls create an unpleasant room impression
bright surfaces, however, pleasantly enhance the room climate
ceilings: at least 30 or 50 lx
walls: at least 50 or 75 lx, even 175 lx
Type of Lighting
Direct lighting
Light falls from the luminaires on the ceiling directly onto the workplace, in part highly directional
Glare suppression is important under flat angles
The ceiling can appear dark (cave effect)
The workplace layout should not allow any shadows
High energy efficiency is achieved for the work area
Indirect lighting
light is directed to the ceiling and walls
it illuminates the workplaces indirectly
effect may appear diffuse through the absence of shadows
the room increases in height
the light is glare free
workplaces can be arranged at random
lower energy efficiency
Indirect/direct lighting
light is directed to the workplace directly and indirectly via the ceiling from suspended luminaires or free standing luminaires
pleasant room visuals
high user acceptance
good contrast ratios
flexible workplace layout with an indirect share of 60%
good combination of energy efficiency and lighting quality
Mellow lighting
the advantages of direct indirect lighting are combined in a ceiling mounted luminaire
possibility of a free workplace layout
glare free lighting that looks good makes for a high acceptance
gives the impression of daylight in a room
good combination of energy efficiency and lighting quality