Lighting Basics

Light calculation example

Luminous flux

(Lumen-1m) is the entire light output emitted by one lamp regardless of the direction.

Luminous intensity

(Candela-cd) is the part of the luminous flux emitted in a specific direction (illumination angle).

Illuminance

(Lux=1m/m²) is the luminous flux per unit of surface area.
1 lux=1lm per m².

Light density

(L=cd/m²) is a measure for the brightness.

Luminous intensity per unit of surface area.

Luminous flux and luminous intensity

can be converted into each other.

The distance between the measuring plane and the lamp is also required when information is given in lux.

Comparison of light sources

Calculation of the lighting conditions in an elevator car

Colour temperature TF

The colour temperature T_F is used to characterise the light colour of a lamp. The comparison object is the black body that is heated up and which assumes very specific colours at specific temperatures.

At the start it is dark red, then red, later orange, then yellow, finally white and at very high temperatures light blue. A specific colour can therefore be defined by giving the temperature of the black body in Kelvin (°K). If the light colour of a lamp is now the same as the colour of the black body, the lamp is assigned its temperature in °K.

An incandescent lamp with a filament temperature of approximately 2800°K emits reddish white light and has practically the same colour temperature as the black body at 2800°K. Incandescent lamps therefore have colour temperatures of approximately 2800°K with their warm white light.

A neutral white fluorescent lamp has approximately 4000°K and a daylight lamp approximately 6000°K.

The following colour temperatures are normally practised in lighting technology:

Incandescent lamps: 2800°K

Tungsten halogen lamp: (3100...3400)°K

Fluorescent lamps: (2800...6500)°K

Mercury vapour high-pressure lamps: (2900...4200)°K

Sodium vapour high-pressure lamps: (2000...2200)°K

Tungsten halogen metal vapour lamps: (3000...6000)°K

Sodium vapour low-pressure lamps: 2000°K

Daylight: 6500°K

Blue sky: 2000 K

In conformity with DIN 5035, distinction is drawn between the three groups below for the colour temperature:

dw Daylight white > 5300°K

nw Neutral white 3300°K to 5300°K

ww Warm white < 3300°K

Please note that the colour temperature of a lamp is only a statement upon the colour appearance of its light, but has nothing to do with the colour rendering characteristics.

The colour rendering index R_a is a measurement value for describing the colour rendering potentials of lamps. As the colour impression of an illuminated object is dependant upon the spectral composition of the light, the spectral characteristics of the light source play a role. In this connection there are major differences due to the different light generated for the different types of lamps. The colour impression perceived by human beings is therefore dependant upon the type of light from the lamp used.

A natural colour impression is only possible when the entire spectrum exists in the light used. When a colour is missing from the spectrum it is not possible to identify the colour of an object that has this colour, it would appear to be grey.

The colour rendering index R_a indicates the extent the colour of an object changes relative to a reference emitter when it is illuminated by a specific lamp. Up to a colour temperature of 5000°K the black body is used as a reference emitter, and natural daylight at different colour temperatures above this colour temperature. Colour deviations are measured for eight different test colours and are defined as a numerical value in the R_a. The maximum R_avalue is 100 when the observed lamp practically does not deviate from the reference light source. When an object is illuminated with this lamp, all of its colours can be identified and appear to be "natural" to an observer. The more the colour rendering index R_adeviates from 100, the worse the colours are rendered on illuminated objects.

The colour triangle

All colours can fundamentally be created through the mixture of three primary colours (colour film, television). The basic condition is, that none of the three primary colours can be mixed through the other two. This means that each colour can be shown in a spatial xyz coordinate system with the colours red, blue and green by using three measurement values.

As the total of the values is x+y+z=1, the system can also be shown in one level according to the CIE. The measurement values are positioned in the colour triangle that includes all real colours, as shown in the illustration. A curved line with the spectral colours 380nm (violet) to 700nm (red) is entered in a xy coordinate system. The connecting line between blue and red is called the purple line.

In the middle is the uncoloured point (white) with coordinates x=y=0.333.

The further a colour location is from the centre, the higher is its colour saturation. Lamp manufacturers indicate the light colour of their lamps with the two coordinates x and y.

Illumination angle/ beam spread

The beam spread is the width of the light beam of a reflector lamp in which the luminous intensity drops to half of the maximum value. It is determined by the design of the reflector. For uniform illumination (general lighting, task lighting), luminaires with a wide beam spread are required.

Strong focussed light is generally required for accent lighting. The characteristic of wide-angled lighting with large beam spreads is described as "flood" and "wide flood", that of narrow focussed lighting a small beam angle, e.g. 10°, as "spot".

Illuminance

Illuminance (symbol: E) is measured in lux (lx) and indicates the amount of luminous flux from a light source falling on a given surface. Illuminance is 1 lux when an area of 1 square metre is uniformly illuminated by 1 lumen luminous flux. Illuminance is measured on horizontal and vertical surfaces by using an illumination photometer. Where a white room and a dark room are provided with the same lighting, the white room appears brighter.

Glare

Glare can be caused directly by luminaires or other surfaces with excessively high luminance such as windows (direct glare) or indirectly from light reflecting from shining surfaces (reflected glare). Glare impairs visual performance (physiological glare) and visual comfort (psychological glare).

Candela

(Abbreviation cd) The unit of measure for luminous intensity in a specific direction from a radiation source since 1940. Candela stands for: candela, photometric SI basic unit of luminous intensity luminous intensity unit.

1 candela equals 1 lux.

DALI (Digital Addressable Lighting Interface)

DALI electronic is a standardised interface for controlling ballasts operating fluorescent lamps by using digital control signals. Unlike the analogue interface (110 V), DALI can address and control operating devices individually.

Dimming

Dimming enables the brightness of individual lamps or groups of lamps to be controlled. It changes the lighting atmosphere, permitting adjustments to suit different room uses (comfort dimming). Increasingly, dimming is also used to save energy (power dimming), e.g. in daylight-dependent office or factory lighting systems. Incandescent lamps and tungsten halogen lamps (230 Volt) can be dimmed with leading phase angle control dimmers, as can low-voltage tungsten halogen lamps operated by magnetic transformers. Lagging phase angle control dimmers are mainly used for dimming low-voltage tungsten halogen lamps on electronic transformers. They are also suitable for incandescent lamps and tungsten halogen lamps (230 Volt). Compact fluorescent lamps and tubular fluorescent lamps need to be operated by dimmable electronic ballasts. LEDs can be simply and effectively dimmed through pulse width modulation (PWM).

DIN 5035

DIN for lighting using artificial light.

DMX

Digital Multiplex = digital control protocol (control signal) inexpensive and versatile, with 512 channels, for controlling for instance dimmers, intelligent lamps, LEDs, or effect lighting

Electronic ballast

Electronic ballasts and dimmable electronic ballasts are used increasingly more instead of conventional or low loss ballasts. They reduce power consumption and make for a high degree of visual comfort. Other advantages: higher luminous efficacy from lamps, flicker-free instant starting, longer lamp life, automatic disconnection of defective lamps.

Colour temperature (°K)

The colour temperature of a light source is defined as the temperature (in degrees Kelvin) at which a black body or Planckian radiator has the same colour appearance as the light source being measured. The values are often only the most similar colour temperatures because a black body cannot assume every colour appearance.

The colour temperatures of normal commercial lamps are in the order of magnitude of below 3,300°Kelvin (warm white), 3,300 to 5,300°Kelvin (neutral white) and over 5,300°Kelvin (daylight white).

Colour rendering

The colour rendering of a lamp indicates the effect its light has on the appearance of persons or coloured objects. This is rated by reference to the "general colour rendering index" R_a, which indicates how natural colours appear under a lamp's light. The colour rendering index is derived from eight frequently found test colours. R_a = 100 is the best rating (=daylight); the lower the index, the poorer the colour rendering properties. Lamps with a R_a index less than 80 should not be used in interior areas where people work or spend lengthy periods of time.

LED

LED stands for "light emitting diode". LEDs are electronic semiconductor components that generate light in the colours red, green, yellow or blue when energised. Blue LEDs can also yield white light when furnished with an internal luminescent coating. LEDs are used in orientation lamps and our SLIMPANEL and also for general lighting purposes. Used in many applications, specific advantages of different LED structural shapes are the long lamp life, maintenance-free, IR/UV-free lighting, low energy consumption, colour stability, stability against vibration.

Luminous efficacy

Luminous efficacy is the measure of a lamp's efficiency. It indicates how many lumens (lm) per watt (W) a lamp generates. The higher the ratio of lumens to watts, the more light a lamp produces from the electricity it consumes. Examples: incandescent lamp 12 lm/W, tungsten halogen lamp 20 lm/W, energy-saving lamp 60 lm/W, tubular fluorescent lamp 90 lm/W.

RGB colour mixing

Colour mixing by using lamps in the primary colours red, green and blue is abbreviated with the colour letters "RGB". RGB colour mixing is particularly ideal for decorative lighting with colour changing. In many cases an additional white light source is used (RGBW colour mixing) to achieve a better white light colour. Fluorescent lamps exist as RGB lamps used for this purpose.

Spectral radiation distribution

Each light wavelength has a specific spectral colour. White light is made up from numerous spectral colours with a different intensity. The spectral radiation distribution characterises lamp types or daylight. In the case of incandescent lamps, for instance, the long-wave red spectral colours dominate, the short-wave blue in daylight.

Spectral colours

The wavelengths of the electromagnetic waves in the visible spectrum range from 380 to 780 nanometres (nm; 1 nm = 109 m). Each wavelength has a distinct spectral colour. These colours can be made visible by a prism, as in the case of a rainbow, which is created by raindrops acting as prisms.

Transformers

Transformers are voltage converters. The transformers that are normally used in lighting reduce 230V line voltage (primary side) to 6, 12 or 24 volts (secondary side). Low-voltage spots and other low-voltage luminaires without built-in transformers need to be operated with individual or collective upstream transformers. Conventional transformer technology operates with different windings on the primary and secondary sides. Toroidal transformers are frequently used. Electronic transformers are smaller, more compact, lighter, quieter and consume less electricity.

UGR

The "Unified Glare Rating" (UGR) method was developed by the International Commission on Illumination CIE (Commission International de l‘Eclairage) to standardise glare assessment worldwide.

VDE

The VDE symbol of the German test and certification institute VDE Technisch Wissenschaftlichen Verbandes der Elektrotechnik Elektronik Informationstechnik e.V. shows that an electrical product meets the standard safety requirements for protection against electrical, mechanical, thermic and other hazards. The VDE also awards the European safety test symbol ENEC.

Ballast

Ballasts are needed for the operation of gas discharge lamps, for instance fluorescent lamps. This is because ignition is followed by massive ionisation of the inert gas or metal vapour in the lamp, which causes a surge in current in the lamp. This would destroy the lamp within a short time. So a ballast is used to limit the lamp current (also during operation).

A distinction needs to be made between conventional ballasts, low-loss ballasts and electronic ballasts. Electronic ballasts or fluorescent lamps are available in dimmable and non-dimmable designs. In energy saving lamps, ballasts are integrated into the screw base; otherwise they form part of the luminaire.

Maintenance factor

The lighting quantity recommendations set out in European lighting standards such as DIN EN 12464-1, e.g. for levels of illuminance, refer to values that need to be maintained. This means that the lighting quantities in question must never fall below them. However, because lamps, luminaires and room surfaces are subject to ageing and soiling, the values that are registered when lighting is new decline as operating time increases. So, to enable a lighting system to be operated longer without additional maintenance work, values on installation need to be correspondingly higher. This is determined by the maintenance factor. Maintenance factors depend on operating conditions as well as on the type of lamps, electrical gear and luminaires used. They need to be defined and recorded by designers (and operators) and form the basis of maintenance schedules. Values required on installation are calculated as follows:

value on installation = maintained value / maintenance factor.

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