Basics of Light and Lighting

Basics of Light and Lighting

Lighting concepts

Basics of Light and Lighting

What is light?

Light and radiation

Light is a form of energy manifesting itself as electromagnetic radiation and is closely related to other forms of electromagnetic radiation such as radio waves, radar, microwaves, infrared and ultraviolet radiation and X-rays.

Light is the electromagnetic radiation that the human eye perceives as brightness, in other words the part of the spectrum that can be seen. This is the radiation between 380 and 780 nanometres (nm), a tiny fraction of the known spectrum of electromagnetic radiation.

Lighting concepts

Basics of Light and Lighting

Basic parameters used in lighting

Luminous flux (F)

Unit of measurement: lumen (lm) All the radiated power emitted by a light source and perceived by the eye is called luminous flux (F).

•

75W incandescent lamp: 900 lm • 39W fluorescent lamp: 3.500 lm • 250W high pressure sodium lamp: 30.000 lm • 2000W metal halide lamp: 200.000 lm Luminous intensity (I)

Unit of measurement: candela (cd) Generally speaking, a light source emits its luminous flux (F) in different directions and at different intensities. The visible radiant intensity in a particular direction is called luminous intensity (I).

Examples (centre of beam): • 5W bicycle lamp without reflector: 2,5 cd • 5W bicycle lamp with reflector: 250 cd • 120W incandescent reflector lamp: 10.000 cd • Lighthouse: 2.000.000 cd Lighting concepts

Basics of Light and Lighting

Basic parameters used in lighting

Luminance(L)

Unit of measurement: cd / sqm Luminance is the only basic lighting parameter that is perceived by the eye.

It specifies the brightness of a surface and is essentially dependent on its reflectance (finish and colour).

Examples: • Surface of the sun: 1.650.000.000 cd/m2 • Filament of a clear incandescent lamp: 7.000.000 cd/m2 • Fluorescent lamp: 5000-15.000 cd/m2 • Road surface under artificial lighting: 0,5-2 cd/m2 Illuminance (E)

Unit of measurement: lux (lx) Illuminance (E) is a measure of the amount of light falling on a surface. It is influenced by the distance the light source is away from the area being illuminated. An illuminance of 1 lux occurs when a luminous flux of 1 lumen is evenly distributed over an area of 1 square metre.

Examples: • Summer, at noon, under a clear sky (equator): 100.000 lux • In the open under a heavily-overcast sky: 5.000 lux • Artificial light, in a well-lit office: 800 lux • Full moon, on a clear night: 0,25 lux Lighting concepts

Basics of Light and Lighting

Basic parameters used in lighting

Luminous efficacy

Unit of measurement: lumens per watt (lm/W) Luminous efficacy indicates the efficiency with which the electrical power consumed is converted into light.

Luminaire efficiency

Luminaire efficiency (also known as the light output ratio) is an important criterion in gauging the energy efficiency of a luminaire. This is the ratio between the luminous flux emitted by the luminaire and the luminous flux of the lamp (or lamps) installed in the luminaire.

Lighting concepts

Basics of Light and Lighting

Basic parameters used in lighting

Lamp Life

Because of slight variations in lamp materials and manufacturing operations, lifetimes of individual lamps differ. The term ‘lamp life’ usually refers to the ‘average rated life’ of a lamp. This is the time after which, on statistical average, half (50%) of a ‘not too small’ number of lamps fail in a controlled operating environment. Each of the lamps in the test group should be of the same wattage, voltage and construction.

Lighting concepts

Basics of Light and Lighting

Basic parameters used in lighting

Colour Appearance & Colour Rendering

Light sources have two different colour properties related to the spectral composition of their emission. One is the apparent colour of the light that the source emits and the other is the effect that the light has on the colours of surfaces. The latter is called

colour rendering

.

When a light source is being chosen, both the colour appearance and the colour rendering properties of the source should be considered in addition to its efficacy and life.

Lighting concepts

Basics of Light and Lighting Colour Appearance

Basic parameters used in lighting

The colour appearance of near white light sources is normally defined in terms of their correlated colour temperature (CCT), expressed in kelvin (K). The higher the correlated colour temperature the cooler the appearance of the light source. An ordinary incandescent lamp, for example, has a colour temperature of 2800K, whereas a daylight fluorescent lamp can have a colour temperature of 6000K.

Figure 1: The CIE Chromaticity Diagram

The International Commission on Illumination (CIE) has grouped lamps into three classes of correlated colour temperatures Colour Appearance Group 1 2 3 Colour Appearance Warm Intermediate Cold Correlated colour temperature, K < 3300 3300 < 5300 > 5300

Lighting concepts

Basics of Light and Lighting

Basic parameters used in lighting

Colour rendering

The CIE general colour-rendering index is a measure, on a scale of up to 100, of the correspondence between the colour of an object (its “self luminous colour”) and its appearance under the nearest reference light source. A light source with an Ra value of 100 displays all 14 test colours exactly as they appear under the reference light source. The lower the Ra value, the worse the colours are rendered.

The CIE general colour-rendering index (CRI) is the most widely accepted measure of the colour rendering properties of a light source.

Initial Illuminance

Initial illuminance is defined as

the value of average illuminance which is initially provided by the lighting system, i.e. with new lamps (aged to 100 hours), clean luminaires and room surfaces.

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Basics of Light and Lighting

Maintenance factor

Maintenance illuminance

is defined as

the average illuminance below which it is necessary to take remedial action in terms of maintaining the lighting system, eg. by replacing the lamps or by cleaning the luminaires, windows, rooflights and room surfaces.

The lighting scheme should be designed with an overall maintenance factor (MF) calculated for the selected lighting equipment, environment and specified maintenance schedule.

The recommended illuminance for each task is given as maintained illuminance.

The maintenance factor depends on the maintenance characteristics of the lamp and control gear, the luminaire, the environment and the maintenance programme.

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Basics of Light and Lighting

The illuminance

The illuminance and its distribution on the task area and on the surrounding area have a great impact on how quickly, safely and comfortably a person perceives and carries out the visual task.

Scale of illuminance

To give a perceptual difference the recommended steps of illuminance (in lx) are according to EN 12665: 20 - 30 - 50 - 75 - 100 - 150 - 200 - 300 - 500 - 750 - 1 000 - 1 500 - 2 000 - 3 000 - 5 000 The required maintained illuminance should be increased when: • visual work is critical; •errors are costly to rectify; • accuracy, higher productivity or increased concentration is of great importance; •task details are of unusually small size or low contrast; •the task is undertaken for an unusually long time;

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Basics of Light and Lighting

The illuminance

The required maintained illuminance may be decreased when: • task details are of an unusually large size or high contrast; •the task is undertaken for an unusually short time.

Key

1- task area 2 -immediate surrounding (band with a width of at least 0,5 m around the task area within the visual field) 3 -background area (at least 3 m wide adjacent to the immediate surrounding area within the limits of the space)

Minimum dimensions of immediate surrounding and background area in relation to task area Lighting concepts

Basics of Light and Lighting

The illuminance

Relationship of illuminances on immediate surrounding to the illuminance on the task area

Measuring level for task area of the workplaces is at 0.75m above floor level !

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Basics of Light and Lighting

Glare

Glare is the sensation produced by bright areas within the visual field, such as lit surfaces, parts of the luminaires, windows and/or roof lights. Glare shall be limited to avoid errors, fatigue and accidents. Glare can be experienced either as

discomfort glare

or as

disability glare

.

Discomfort glare

UGR – stands for

Unified Glare Rating The recommended limiting values of the

UGR :

10, 13, 16, 19, 22, 25, 28

Lighting concepts

Basics of Light and Lighting

Electric measuring units

Volt

The Volt (V) is the unit of measurement stabilised by the International System of Measurement for quantifying differences in electrical potential. It is defined as the potential difference existing between the extremes of one conductor in which power of 1 watt is released when current equal to 1 ampere is fluxing inside.

Watt

The Watt (W) is the unit of measurement of energetic flux and represents the power emitted, transported or received in the form of radiation.

Ampere

The Ampere(A) is the unit of electric current.

P(power) (Watt) = U(voltage)(volts) x I( current)(amps) x cos Ø

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Basics of Light and Lighting

Terms and definitions

•

Activity area -

area within which a specific activity is carried out •

Background area -

area adjacent to the immediate surrounding area •

Immediate surrounding area -

band surrounding the task area within the visual field •

Roof light -

daylight opening in the roof or a horizontal surface of a building •

Shielding angle -

angle between the horizontal plane and the first line of sight at which the luminous parts of the lamps in the luminaire are directly visible •

Task area -

area within which the visual task is carried out •

Visual task -

visual elements of the activity undertaken

Work station -

combination and spatial arrangement of work equipment, surrounded by the work environment under the conditions imposed by the work tasks

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Basics of Light and Lighting

Luminous environment

Lighting requirements are determined by the satisfaction of three basic human needs: •

visual comfort

, where the workers have a feeling of well-being; in an indirect way this also contributes to a higher productivity level and a higher quality of work; •

visual performance

, where the workers are able to perform their visual tasks, even under difficult circumstances and during longer periods; •

safety

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Basics of Light and Lighting

Lighting requirements for interior areas, tasks and activities

Lighting concepts

Basics of Light and Lighting

Lighting requirements for interior areas, tasks and activities

Lighting concepts

Basics of Light and Lighting

Lighting requirements for interior areas, tasks and activities

Lighting concepts

Basics of Light and Lighting

Lighting requirements for interior areas, tasks and activities

Lighting concepts

Basics of Light and Lighting

Lighting requirements for interior areas, tasks and activities

Lighting concepts

Basics of Light and Lighting Lighting concepts