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CLOSE THIS BOOKLighting Installation - Basic vocational knowledge (Institut fr Berufliche Entwicklung, 164 p.)
2. Elements
VIEW THE DOCUMENT2.1. Basic Terms in Lighting Engineering
VIEW THE DOCUMENT2.2. The Eye and its Visual Capacity
VIEW THE DOCUMENT2.3. Colour, Light and Space
2.4. Quality Characteristics of Lighting
VIEW THE DOCUMENT2.4.1. Indoor Lighting
VIEW THE DOCUMENT2.4.2. Outdoor Lighting

Lighting Installation - Basic vocational knowledge (Institut fr Berufliche Entwicklung, 164 p.)

2. Elements

2.1. Basic Terms in Lighting Engineering

Radiation - general

Emission or transmission of energy in the form of electromagnetic waves or corpuscles.

These electromagnetic waves or corpuscles themselves.

The wavelength of this radiation is unlimited.

Radiation - visible

Radiation causing visual sensation immediately and directly. The visible radiation comprises the energy in the wave bands between 380 and 780 nm.

Light

Characteristic of all perceptions and sensation the visual organ is capable of mediating.

Radiation suitable for exciting the visual organ.

Relative luminosity factor

The ratio of the radiant flux with the wavelength Lambda (m) and the radiant flux with the wavelength Lambda both radiations causing the same brightness impression in certain photometrical conditions.

Lambda (m) has to be selected in such a way that the maximum of this ratio is equal to 1.

The graphic representation of this ratio shows the spectral photopic eye response curve for daylight and night vision (Fig. 1). For the purpose of phototechnical evaluation of all physical values these must be related to the mentioned curve.

Therefore, the phototechnical formula symbols get the index ‘v’, whereas the physical values bear the index ‘e’ for ‘energy’.


Figure 1. Spectral-response function of the eye depending on the wavelength

1 for cone vision (day vision)
2 for rod vision (night vision)

Luminous flux

Value derived from the luminous flux in such way that the radiation is assessed according to its effect on a selective receiver the spectral sensitiveness of which is given by the standardized degree of brightness.

Unit lumen (lm)

Lumen is the internationally agreed unit of the luminous flux.

The luminous flux characterizes the light power.

Light efficiency

Quotient out of the luminous flux and the wattage applied.

Unit lumen per watt

Light intensity

Quotient out of a luminous flux emitted by a light source into a solid angle element around the considered direction and this solid angle element.


Figure 2. Representation of light intensity

1 light source, 2 direction of view, 3 solid angle, 4 portion of the luminous flux which is registered from the direction of view

For calculating the illumination it is important to know in what direction the lighting fitting distributes the luminous flux.

That is to say one must know the spatial distribution of the luminous intensity of the illuminator. For this, the luminous intensity is represented as a radius vector in a polar diagram.

All the vectors start from the same point - pole -; their respective length is proportional to the values of the luminous intensity in the various directions. By meridian sections one gets the light distribution curve (LVK) in these planes.


Figure 3. Basic representation of the light distribution curve

1 light intensity in candela

With the representation of the solid of light distribution by light distribution curves with many lighting fittings one cannot manage with one sectional axis; it is necessary to determine plane systems. Three plane systems are preferred.

- Planes the lines of intersection of which stand on one supposed illuminator axis and lie in a horizontal plane through this axis.

The planes a re called A-planes, the angle of swing of the planes is represented by beta.


Figure 4. Light distribution curve (A plane)

1 illuminator axis
2 rotation axis
3 beta = 40 degrees
4 beta = 20 degrees
5 beta = 0 degrees
6 light distribution curve in the A plane

- Planes the lines of intersection of which coincide with the supposed illuminator axis. These planes are called B-planes, the angle of swing is marked by alpha. The alpha- and beta-angles are counted from 0 to +- 180 degrees. The direction of a luminous intensity I in the A-planes system is clearly defined by the value A (beta, alpha), which is equivalent to beta = 40 degree and alpha = 30 degrees. The direction of a luminous intensity I in the B-planes system is clearly defined by the indication of B (alpha, beta), which is - in this example - alpha = 30 degrees and beta = 40 degrees.


Figure 5. Light distribution curve (B plane)

1 illuminator and rotation axis, 2 alpha = 40 degrees, 3 alpha = 20 degrees, 4 alpha = 0 degrees, 5 light distribution curve in the B plane.

- Planes the lines of intersection of which stand vertically on the illuminated surface and which pass through the centre of the illuminator.

These planes are called C-planes; the angle of swing is called gamma and counts from 0 to 360 degrees - semiplanes.


Figure 6. Book-leaf representation of a low-frequency illuminator in the A plane

1 (candela divided by 1000 lumen), 2 measuring plane, 3 beta = 0 degrees, 4 beta = 50 degrees.


Figure 7. Channel flood lantern with light distribution curve


Close-radiant with an illuminator efficiency of 0.74

1, 2 radiation planes


Wide beam with an iliuminator efficiency of 0.72

Luminance

Luminance - in one direction, at one point of a radiating or irradiated surface, or at a point of an optical path.

Quotient of the luminous flux leaving a surface element enclosing the respective point, hitting the surface element or penetrating it and spreading within a solid angle element in a given direction and of the product of the transilluminated solid angle element and the surface element on one plane vertically to the direction of the radiation.


Figure 8. Representation of luminance

1 light intensity for epsilon, 2 transilluminated solid angle element (surface element), 3 vertical orthogonal projection of the surface element

Unit of candela per square metre

Illumination

Quotient of the luminous flux received by a surface element which contains the point considered and of the surface of this element.

Unit of lux (lx)

Illumination is that value in lighting engineering which is mainly used as the basis of projecting indoor and outdoor lighting installations, except street lighting installations.

In this context it is mostly necessary to picture to oneself the distribution of illumination. In many cases, the indication of the average illumination is sufficient. In this case, the surface the average illumination is related to must be accurately marked off.

For characterizing the local evenness it is required to know the maximum and minimum illumination on the calculated surface with outdoor installations. Often it is also important to know the evenness on a number of vertical planes and to find out the minimum and average values of certain vertical planes. After having measured or calculated the illumination in a number of points of one plane, the values in these points can be projected vertically as vectors on the surface (measuring plane); the values are given by the length of the vectors. The enveloping surface of these vectors is the illumination shape that gives a picture of the distribution of illumination on the measuring plane.

By connecting the points of the same illumination within this shape the representation becomes more illustrative - isolux surfaces.


Figure 9. Illumination figure of a lighting fitting fixed to a lamp pole by a holding fixture, useful height = 9 m

1 illumination in lx, 2 width of the measuring plane in m, 3 length of the measuring plane in m

In practice, sections in different planes of the shape are sufficient. The vertical section produces the rectangular illumination diagram.

Table 1. Survey of the basic values, their symbols, units and relations in lighting engineering

Basic value

Symbol

Unit

Abbreviation

Relations

Luminous flux

F

lumen

lm


Light quantity

r

lumen-second

lms

Light intensity

I

candela

cd

Illuminance or illumination

E

lux

lx

Luminance or luminous density

L

candela/square metre

Light efficiency

h

lumen/watt

Table 2. Luminance in various systems of units


sb

asb

L

fl

1

10-4

p

p x 10-4

0.2919

1 stilb (sb)

104

1

p 104

p

2.919x103

1 apostilb (asb)

1

10-4

9.291x10-2

1 lambert

104

1

9.291x102

1 foot-lambert (fL)

3.426

3.426x10-4

10.764

1.0764x10-2

1

Table 3. Illumination or illuminance in various systems of units


lx

ph

fc

1 lux (lx)

1

104

9.291x10-2

1 phot (ph)

104

1

9.291x102

1 footcandle (fc)

10.764

1.0764x10-3

1

In addition to the mentioned basic units distinguishing marks - materials indices - are required, which mainly characterize the building materials in lighting engineering. These include materials for lamps and lighting fittings and all materials influencing the illumination and entire impression of a room and which exert an influence especially on the mood of the people staying in this room, e.g. machines, surfaces of the room, work clothes, etc.

The qualities of a material relevant for illumination engineering are expressed and represented by:

Reflection, transmission and absorption

This is the throwing back or passing through of a radiation by or through a surface or medium without any change of frequency within the monochromatic portion of the radiation and transformation of radiant energy into another form of energy by interaction of light with matter. There are different types of reflection and transmission:

Specular reflection

Reflection without scattering according to the rules of optical reflection such that all reflected rays have the same direction.


Figure 10. Directed reflection, transmission

Diffuse reflection

The reflection of rays from a surface such that the reflected rays have various directions, as far as the rules of optical reflection do not become noticeable macroscopically.


Figure 11. Diffuse reflection, transmission

Mixed reflection

Simultaneous specular and diffuse reflection.


Figure 12. Mixed reflection, transmission

Perfectly diffuse reflection

Diffuse reflection such that the reflected radiation is evenly distributed in all its directions as to radiant intensity and luminance per unit area - Lambertian light source.

To the types of transmission the respective definitions apply.

Among the mixed reflections also counts the term of Gloss (of a surface)

Quality of a surface such that - by specular reflection or an acute reflection indicatrix - it shows bright reflected lights or the reflected pictures of bright things.

Gloss can essentially support the recognition of a form, but it may as well impede the recognition of details.

Therefore, this phenomenon must be paid special attention to when a lighting installation shall be constructed.

Table 4. Characteristics of illuminating engineering materials - glass -

Material

Thickness mm

Transmission factor

Reflection factor

Absorptance

Remarks

Crystal

2-4

0.9-0.92

0.06-0.08

0.02-0.04


Plate glass

1-4

0.90-0.92

0.06-0.08

0.01-0.03


Raw glass, greenish

4.1-9.1

0.85-0.90

0.06-0.07

0.02-0.08


Wired glass

5-7

0.53-0.70

0.1-0.3

0.17-0.20


Figured glass

3-6

0.55-0.85

0.07-0.25

0.03-0.20


Frosted glass sand-frosted

1.8-4.4

0.77-0.82

0.09-0.14

0.08-0.10

frosted towards the light source smooth towards the light source



0.70-0.75

0.11-0.16

0.12-0.15


Frosted glass, acid-frosted

2.0-6.7

0.83-0.91

0.07-0.10

0.02-0.08

frosted towards the light source smooth towards the light source



0.78-0.89

0.06-0.11

0.02-0.06


Frosted glass, on both sides, acid-frosted

1.3-2.2

0.75-0.90

0.06-0.11

0.04-0.19

Opaline glass

1.1-4.5

0.10-0.38

0.4-0.7

0.12-0.30

compact-opaque, without directed transmission



0.37-0.47

0.46-0.57

0.07-0-11

opaque with directed transmission under 1 %



0.13-0.31

0.55-0.78

0.04-0.10

opaque with directed transmission over 1 %

Opaline glass, on one side

1.3-2.8

0.20-0.44

0.45-0.68

0.10-0.23

opaque to wards the light source



0.19-0.42

0.46-0.69

0.10-0.23

smooth towards the light

Opaline flashed glass

1.8-6.2

0.22-0.66

0.30-0.63

0.03-0.28

double-layer glass

Opaline flashed glass, frosted on both sides

2.2-3.2

0.24-0.68

0.36-0.53

0.16-0.27

opaque towards the light source



0.24-0.51

0.30-0.46

0.15-0.36

clear towards the light source

Opaline flashed glass, in three layers

1-1

0.49-0.58

0.4-0.5

0.04-0.06

2 clear-glass layers with very thin, well-scattering opal-glass layer in the middle

Table 5. Characteristics of illuminating engineering materials - metals -

Material

Reflection factor

Absorptance

Aluminium, polished

0.60...0.72

0.28...0.40

Aluminium, polished and anodized

0.75...0.90

0.10...0.25

Aluminium, dulled

0.55...0.60

0.40...0.45

Aluminium, foil

0.80...0.87

0.13...0.20

Silver, polished

0.85...0.94

0.06...0.15

Glass silver mirror

0.70...0.90

0.10...0.30

Glass aluminium mirror

0.90...0.94

0.08...0.10

Platinum, polished approx.

0.62 approx.

0.38

Gold, polished approx.

0.70 approx.

0.30

Nickel, polished

0.53...0.63

0.37...0.47

Nickel, dull

0.45...0.55

0.45...0.55

Chromium, polished

0.60...0.70

0.30...0.40

Chromium, dull

0.40...0.45

0.55...0.60

Rhodium, polished

0.70...0.78

0.22...0.30

Copper, polished

0.48...0.60

0.40...0.52

Brass, Chromium-plated

0.61...0.62

0.38...0.39

Brass, chromium-plated, dull

0.52...0.55

0.45...0.48

Steel, polished

0.55...0.60

0.40...0.45

Tin plate

0.67...0.69

0.31...0.33

Enamel, white

0.65...0.80

0.20...0.35

Enamel, white, from synthetic resine

0.85...0.90

0.10...0.15

Table 6. Characteristics of illuminating engineering materials - paper and paint coats -

Material

Transmission factor

Reflection factor

Absorptance

Paper


Drawing paper


0.75...0.85

0.15...0.30


Cardboard, white


0.70...0.80

0.20...0.30


Board, white, slightly coloured


0.61...0.65

0.35...0.39


Paper, white (print)

0.05...0.20

0.60...0.70

0.12...0.21


Vellum paper, noncoloured

0.35...0.55

0.45...0.48

0.05...0.15


Vellum paper, slightly toned

0.14...0.41

0.36...0.38

0.22...0.50

Paint coats


Oil, white


0.76...0.85

0.15...0.24


Lime,

white


0.70...0.85

0.15...0.30



ivory-coloured


0.60...0.70

0.30...0.40



cream-coloured


0.56...0.72

0.28...0.44



straw-coloured


0.55...0.67

0.33...0.45



chromium-yellow, pure


0.48...0.52

0.48...0.52



gold


0.44...0.59

0.41...0.56



medium-brown


0.27...0.41

0.59...0.73



light green


0.40...0.67

0.33...0.60



dark green


0.10...0.22

0.78...0.90



grass green


0.12...0.20

0.80...0.88



light blue


0.31...0.55

0.45...0.69



turquoise


0.10...0.15

0.85...0.90



ultramarine


0.07...0.10

0.90...0.93



bright red


0.32...0.55

0.45...0.68



dark-red


0.10...0.27

0.73...0.90



vermilion


0.20

0.80



carmine


0.10

0.90

Table 7. Characteristics of illuminating engineering materials - various building materials -

Material

Thickness mm

Transmission factor

Reflection factor

Absorptance

Fabrics


Cambric, white, linen

0.50...

0.50...0.60

0.30...0.40

0.07...0.10


Cotton, white


0.25...0.40

0.30...0.40

0.23...0.40


Shirting, white


0.28...0.35

0.57...0.68

0.04...0.08


Silk, white


0.57...0.71

0.25...0.38

0.01...0.06


Silk, coloured


0.27...0.80

0.05...0.25

0.13...0.54


Velvet, black


0.02...0.10

0.90...0.98

Wood


Plywood



0.38...0.45

0.55...0.62


Oak,

light



0.25...0.33

0.67...0.75



dark



0.15...0.25

0.75...0.85


Pear tree



0.20 approx.

0.80 approx.


Walnut



0.15...0.20

0.80...0.85


Maple-tree



0.27 approx.

0.73 approx.


Mahogany



0.07 approx.

0.93 approx.


Ash-tree



0.30 approx.

0.70 approx.


Birch-tree, waved



0.40 approx.

0.60 approx.

Natural and artificial stones


Marble, pure white

more than 5


0.75...0.83

0.17...0.25


soaked

3...5

0.20...0.40

0.30...0.45

0.10...0.35


mottled

3...7

0.04...0.20

0.48...0.70

0.18...0.48


Alabaster

8...13

0.17...0.30

0.45...0.67

0.14...0.33


China, white



0.60...0.80

0.20...0.40


Gypsum plaster (stucco)



0.75...0.89

0.11...0.25


Cement lime plaster



0.40...0.60

0.40...0.60


Mortar



0.40...0.45

0.55...0.60


Bricks,

new, red



0.10...0.20

0.80...0.90



old, red



0.02...0.05

0.95...0.98



new, yellow



0.20...0.30

0.70...0.80

2.2. The Eye and its Visual Capacity

The image of the environment is perceived and its physiological and psychological processing and assessment for experience of life is effected by the

Visual organ

It is the entirety of eye, optic nerve and cerebral cells that transforms the light stimulus into those nerve excitations which are the subjective correlate of the visual perceptions.

At first, the external light stimulus hits the eye.

Eye

This is the part of the visual organ which perceives the image of the external world and which transforms this image into nerve excitation.


Figure 13. Horizontal section through the human eye

1 cornea (transparent), 2 crystalline lens of the eye, 3 anterior eye chamber, 4 iris, 5 ciliary body, 6 sclerotic coat, 8 retina, 9 vitreous humour, 10 fovea centralis, 11 optic papilla, 12 optic nerve

The most important part of the eye is the retina.

Retina

The light-sensitive membrane of the eye consisting of the light receptors - cones and rods - and nerve cells. The latter lead the excitation to the optic nerves. Cones and rods are embedded in the retina.

Cones

Especially light-sensitive elements of the retina which presumably enable light and colour vision of the light-adapted eye - day vision.

Rods

Especially light-sensitive elements of the retina which most probably enable vision by the darkness-adapted eye.

The rods are not likely to contribute to colour vision. (Night vision). The distribution of cones and rods on the retina is different.

In the region of the breakthrough of the visual nerve and the choroid through the cornea there are neither cones nor rods.

For this reason, this part of the eye is called the “blind spot”. On the level of the optical axis of the eye there is a concentration of rods. Here is the region of sharp vision. This part of the retina is called fovea centralis.

Fovea centralis

Thinned and therefore concave central part of the yellow spot showing almost only cones. Region of accurate vision. It is corresponding to a visual angle from 0.017 to 0.035 rad (1 to 2 degrees) in diameter.

From this part of the retina towards its periphery the portion of rods in the retina grows continuously. Finally, there are only isolated cones in the periphery of the retina.

With the help of these cones and rods, which have a very differentiated sensitiveness to light, man is able to orient himself in bright sunshine and in moonlight as well. However, experience has shown that the adaptation, especially to a dark environment, takes a certain time. The ability of the human visual organ to adapt itself to light is called

Adaptation

The process of the visual organ adapting itself to luminances and chromatic stimuli in the range of vision. Condition achieved after completion of the process. The term ‘light adaptation’ is used if the luminance is at least a few candela per square metre; if it is less than some hundredth parts of a candela per square metre one speaks of ‘dark adaptation’.

With a physical radiation in the range from 380 to 780 mm seeing is enabled by the cones and rods.

Seeing; visual perception - specific excitation of the sensory system of the eye.

Recognition of the surrounding world by sensory impressions caused by incident radiation.

In this process, rods and cones are included separately or in common because they absorb the incident radiation. The electric pulses created during the absorption of the radiation are led to the brain via the optic nerve, which is the junction of the ends of cones and rods, and - in the optic centre - result in conscious perception.

Perception

Complex content of the consciousness resulting from sensorial impression and contents of the memory (shape).

Especially, the visual perceptions drop in the ideas we form of the existence, form and position of external things.

Since, with the process of seeing, it is not as often a question of stationary things as it is a question of objects in motion, the time for which these objects come into vision is of special importance. The movement of the things, that is to say the impression of movement, may also be caused by the movement of the eyes. Thus, the speed of perception must be considered as a decisive value in the process of seeing.

Speed of perception

Reciprocal of the interval of time passing between the moment of objective exposure of a thing to the eye and the subjective perception of the image.

This term is equivalent to that of ‘speed of perception of form’. Another parameter in the context of the perception of the environment is colour.

Colour

- Colour sensation: That characteristic of a visual sensation which makes it possible to distinguish between two neighboring parts of the viewing field equal as to their size, shape and structure but different in their spectral condition.

- Colour valence: Characteristic of a visible radiation which makes it possible to distinguish between to neighboring parts of the viewing field equal as to their size, shape and structure but different because of the different spectral condition of the respective radiations.

Colour sensation is only possible if object, physical radiation and action of the eye concur. Colour sensation can be influenced by the colour of the object as well as by the spectral composition of the radiation. In general, the colour of the object is called body colour.

Body colour

Colour of a non-luminous object: colour sensation caused by a non-luminous object.

The CIE definition of the term of ‘seeing’ speaks of the ‘recognition’ of differences in the surrounding world. This can be put in more concrete terms: The eye distinguishes on the one hand brightness and luminance contrasts and on the other hand colour contrasts.

Contrast

- Subjectively: Mutual influencing of two immediately neighboring or successive visual impressions - simultaneous contrast, successive contrast.

- Objectively: The size of the luminance contrast defined by formulae.

If the visual function is reduced by an unfavourable distribution of luminance, too high luminance or too great spatial or temporal luminance contrasts causing an unpleasant feeling - discrimination threshold, etc. - we speak of dazzle.

Literature distinguished between two main types of dazzle:

Psychological dazzle

Kind of dazzle causing an unpleasant sensation without a distinct reduction of the visual capacity being necessarily linked with this feeling.

Table 8. Glare terms according to Schober

Term

Meaning

Examples

Adaptation glare

Sudden change of the luminance level in the field of vision

Flickering of the lighting installation, temporal sunlight incidence with partially clouded sky

Relative glare

Too great simultaneous local luminance differences in the field of view

Light working places in a dark room

Absolute glare

Luminance exceeding the adaptation ability of the eye

Luminance of the sun, the arcs of highest-pressure xenon or mercury lamps, of the full headlight beam of a car at night

Direct glare

Glare caused by light sources

Bare filament lamps, fluorescent lamps and high-pressure mercury lamps near the field of view

Indirect or reflection glare

Glare caused by the ghost image of a light source or by too bright light-scattering surfaces in the field of view

Reflection of the luminance of lamps on the material worked, e.g. a turning part, keys of a typewriter and others, sky luminance of the windows with writing-tables standing in front of them (see also example of indirect glare)

Surround field glare

Glare source is situated at the circumference of the field of view

Physiological dazzle

Kind of dazzle leading to a reduction of the visual capacity without necessarily causing an unpleasant sensation simultaneously.

With moving objects, flicker may cause a special effect:

Stroboscopic effect

Illusion of motion consisting in the fact that objects in motion appear as resting or in a condition other than their real one because they are illuminated by periodically variable light of a suitable frequency.

2.3. Colour, Light and Space

The aims of illumination include the following components:

Light (light source, lighting fitting), colour (colours of the ceiling, walls and furniture etc.) as well as the spatial conditions (dimensions of the room, measuring planes). These have to be considered in order to achieve an economical illumination.

The efficiency of the lighting installation is determined by the possibility of directing the light of the respective light source, to diffuse it - according to purpose - or to reflect it.

A distinction is made between illuminator efficiency and degree of the effect of depth. Both together result in the efficiency of illumination.

Efficiency of the illuminator

The illuminators shall fulfill their task of directing the luminous flux with the lowest possible light flux loss. Light flux losses are caused by losses in transmission and reflection at lighting fitting components. The efficiency of an illuminator (optical efficiency) is the ratio of the light flux emitted by the illuminator Phi (2) and the sum of the light flux generated by the individual lamps within the respective illuminator Phi (1).

Degree of the effect of depth

For projecting indoor lighting installations according to the light flux method, the degree of the effect of depth Eta (R) has to be determined. It considers the effects of the room on the direction of the light flux on the plane of calculation Phi (3). It depends on the proportions of the room, the values of the degree of reflection of the limiting surfaces of the room and the mode of construction and is defined by

Degree of illumination efficiency

The degree of the illumination efficiency Eta (B) is calculated from the degree of efficiency of the illuminator Eta (L) and the degree of the effect of depth Eta (R):

Eta(B) = Eta(L) x Eta(R).

Thus, the degree of illumination efficiency is the ratio of the light flux Phi(3) reaching the area of use and the lamp-emitted light flux Phi(1):

The degree of illumination efficiency has very wide limits; in practice values between 0.05 and 0.9 are to be found.

Light and colour

The use of colours in a working room deserves more and more attention because due to the ever more sophisticated processes of work the required illumination values at work places amount to 1000 lx and more. A consequence of the putting into practice of so great an illuminance is that the luminance in the range of vision can no more be an optimal one, if no coloured surfaces are used in the working room.

The spectral composition of the light energy emitted by the lamps is different depending on the kind of light generation - temperature radiators or gas-discharge light source - and on the type of lamp which is used.

In warm light colours also warm body colours make themselves felt in a pleasant way, whereas the low proportion of short-wave radiation of these light sources more or less “kills” cold colours such as bluish green, blue and purple. With neutral-white light sources, all colour shades are assessed as equal. Lamps of this group are called ‘safe light colours’.

As background colours - wall and ceiling colours - white or light colours of little intensity such as pastel colours are preferred. Here, one can speak of ‘safe wall colours’. On the other hand, very dark background colours are accepted, too. Colours of a medium intensity and brightness are estimated least.

The question whether or not the colour of an object is felt as pleasant or unpleasant mainly depends on the colour of the background before which the object is presented. Therefore, a well chosen background colour may counteract even a ‘bad light source’ as well as, the other way round, a disadvantageous background colour may spoil the effect of a ‘good light source’.

Independent of the light colour and the colour of the background, the cold colours blue, bluish green, green and purple are preferred as object colours. Therefore, they can be understood as ‘safe object colours’. On the scale of assessment they are followed by red, yellow ranks last.

Whereas for the background colours very little intensity is preferred, very intensive colours are suited best for the objects.

In general, women are inclined to choose warmer colours such as red, yellowish red, and yellow in contrast to men who give preference to the green and bluish green shades.

The colours of food, as a rule, look better in warm light than in colder light.

Two neighboring colours, generally, are felt as harmonious only if they are similar in their shades. The more the colour shades are distant from each other on the hue circle the less harmonious is the impression of the combination.

In spite of the above statements it must be said that the colours in a room create a satisfactory atmosphere only if they are lively and diversified.

Simple repetition of a design and of colours which have proved good, decorative and useful often leads to boredom, monotony and thus to the opposite of the desired effect.

2.4. Quality Characteristics of Lighting

2.4.1. Indoor Lighting

Decisive of the impression an illuminated room leaves is the distribution of brightness and colours in it, i.e. the ‘colour climate’ which by the CIE dictionary is defined as follows:

The colour climate is the physiologically existing and psychologically active atmosphere of a room resulting from light (illumination and its distribution, kind of illumination and light colour) and from colour (shade, degree of intensity, colour rendition and area distribution in a room) in connection with form.

The following criteria of assessment are applied to indoor lighting:

- physiological-optical assessment taking into consideration the visual work and thus physiological problems relating to work;

- psychological assessment concerning the agreeableness of lighting;

- hygienic assessment as to whether or not the light in its quality and quantity is healthy.

The quality characteristics of lighting are subdivided in four groups.

Table 9. Quality characteristics of illumination

Quality characteristics

Quality factors

Illuminating level

Illumination


Illumination distribution


Luminance distribution

Glare avoidance

Glare limitation with direct glare


Avoidance of reflection glare

Shadowyness and light direction

Shadow depth, gloss

Light and colour

Light colour


Colour rendition


Table 10. Assessing methods and criteria for determining the optimum illumination

Physiological investigations in the relations between illumination and working efficiency

Investigations have shown a direct connection between illumination and efficiency. It is to be seen that the efficiency increases depending on the illumination and the size of the detail of a visual task.

With an increasing fineness of the details, an intensified illumination leads to an increase in efficiency. In this context, of course the level of initial illumination must not be overlooked.

Since the physiological investigations in connection with efficiency are carried out over longer periods of time, conclusions can also be drawn with respect to fatigue and lighting as far as fatigue decreases with increasing illumination.

The investigations and findings in connection with the illumination intensity refer to an average visual capacity. The special conditions of seeing at an advanced age and the differences in individual visual capacity were very little considered. An immediate connection between visual capacity - especially visual acuity - and age has been proved. From the fact that younger people often have better eyes it cannot be concluded that older people are less efficient, because there are essential other factors to be considered such as vocational experience and the general attitude towards working. The losses in visual acuity that occur along with the advance in years of life can be balanced to a far extent by an increased illumination in the course of which the specific characteristics of the respective work must not be forgotten.

Glare and glare limitation

Visual capacity is reduced if there are too great differences in luminance within the field of view. In such case one speaks of glare or dazzle.

With indoor lighting fittings it is mostly a question of psychological glare. It causes a feeling of uncomfortableness in man.

The assessment of psychological glare and the limitation of it to a permissible degree is an important criterion of the quality of indoor lighting installations. It is distinguished between the glare caused directly by the illuminators in the room - direct glare - and the glare resulting from too great luminances in the field of view, from reflection and/or areas of great luminance within the range of working.


Figure 14. Radiation angle for glare evaluation

1 height difference between eye and illuminator, 2 critical range of the radiation angle, 3 distance of the last visible illuminator

2.4.2. Outdoor Lighting

Similar to indoor lighting, also here the quality depends essentially on the luminance and its distribution in the field of view. Some statements made on indoor lighting also hold good for outdoor lighting.

Not all factors influencing the quality of illumination can be expressed in terms of quantity yet. Therefore, it is important to understand the correlations of the influencing factors in their effect on the quality of lighting. The most important quality characteristics are:

- luminance
- evenness of luminance
- illumination and evenness of illumination
- glare limitation
- optical guidance and additional information
- light design
- operation.

Luminance

Luminance determines the impression of brightness and the visual perception of the range of work or the traffic area. Seeing is the “recognition of differences in the surrounding world...”.

This is a question of recognizing differences in luminance - brightness differences - and differences in colour. Differences in colour - colour contrasts - generally play a subordinated role in outdoor lighting, because in outdoor areas they are less often represented and - with a low level of illumination - they may be beyond the threshold of visibility at that.

With an increasing luminance, visibility increases, too. This is to say, the eye becomes more sensitive to differences. A further increase in the adaptation luminance of outdoor lighting causes an essential increase in the sensitiveness to differences. For the time being, the luminance of street lighting is approximately 1 candela per square metre. The visual angle can mostly not be influenced. The luminance of the surrounding field can be increased only by much expenditure. Therefore, the creation of favourable contrast conditions is an important task.

Questions for repetition and knowledge test

1. What is the meaning of the term of ‘light flux’?
2. What is understood by ‘illumination efficiency’?
3. By what factors is the quality of a lighting installation determined?

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