LIGHTING KNOWLEDGE

Construction and operating mode determine the appliance class of luminaires. The scope of protective measures against electric shock is described by three protection classes according to DIN VDE 0711:

• Appliance Class I:
  Luminaires for connection to the mains-side protective conductor: the symbol is attached to the connection point.
• Appliance Class II:
  Luminaires with additional or reinforced insulation: they do not have a protective conductor connection.
• Appliance Class III:
  Luminaires for operation with protective extra-low voltage

In the industrial production of LED chips, tolerances can occur within a batch, e.g. in the light color. Therefore, the LEDs are measured and sorted into bins depending on the tolerance class. Especially for white LEDs, this "binning" process is important.

Selection criteria are.

• Luminous flux (lumens, lm)
• Color temperature (Kelvin, K)
• Color location
• Forward voltage (volts, V)

Uniform brightness and light color can only be guaranteed with carefully selected binning groups. A good binning process therefore represents an important quality feature of LED chips.

The term "blue component" is used to describe the melanopic effect of light. This lies in the spectral range between 450 and 530 nanometers (nm). In this wavelength range, light appears to the human eye as blue to blue-green. The "blue component" is a portion of the white light that is formed by the entire spectrum. Cold white or daylight white lighting contains a higher blue component than warm white lighting, which is why stronger biological effects can be expected here.

The color rendering index (CRI) characterizes the color effect that the light of a light source produces on colored surfaces, i.e. how naturally colors are reproduced in the light of a light source. The best value corresponds to CRI=100. The lower the color rendering index, the worse the colors are reproduced. In areas with special requirements, such as color testing in industry, CRI>90 is optimal. As a general rule, CRI=80 should not be undercut indoors.

The color temperature in Kelvin (K) describes the light color. Ordinary illuminants are available in the color temperatures warm white (< 3300 K), neutral white (3300 to 5300 K) and daylight or cool white (> 5300 K).

Magnetic ballasts are very robust and "unbreakable" in practice, but they consume much more energy compared to ECGs. That is why the first generation of conventional ballasts (CCGs) has not been allowed to be marketed in the EU since 2005 due to their poor energy efficiency.

Since 2017, only electronic ballasts with energy class A1 and A2 may be placed on the market.

The term converter is used in electrical engineering for power converters. Power converters use electronic components to convert one type of current into another: Alternating current to direct current (rectifier), direct current to alternating current (inverter). Converters that can be operated either as DC or AC power converters are called inverters.

DALI is a standardized interface for controlling electronic ballasts via digital control signals. With a small number of lines, the DALI interface can control many luminaires individually even over long distances.

In addition, DALI can be easily integrated into higher-level building system technologies, such as KNX, EIB (European Installation Bus) or LON (Local Operating Network).

Advantage for the installer:
With DALI, a wiring change, as required by analog interfaces with 1...10V technology, is not necessary; the complete lighting in a room can be controlled with only one gateway node. DALI not only takes care of switching and dimming the light. The system is also suitable for controlling light colors with LEDs, fluorescent lamps or metal halide lamps.

Daylight equivalent effect is used in the context of non-visual light effects to refer to the light that prevails outdoors but in an area protected from direct sunlight. In particular, the term refers to the visible components of radiation (= light) and ignores UV or infrared radiation components.

Natural daylight is considered the light source that ensures an optimal supply of the biologically effective light components. For the evaluation of artificial light sources, therefore, daylight D65 was chosen as the reference light to which the biologically effective radiation components refer.

The brightness of individual luminaires or groups of luminaires can be controlled by dimming the light sources used. Dimming changes the mood of the light and allows it to be adapted to different uses of the room (comfort dimming). Dimming is also used to save energy (energy dimming), e.g. for daylight-dependent lighting in offices or industrial halls.

LED modules are dimmed either by lowering the amplitude of the forward current (=current dimming) or by reducing the average value of the forward current (=pulse width modulation, PWM). The current flow of the LED is thereby rhythmically interrupted after a certain PWM frequency. The larger the current gaps between the current phases, the lower the effective or average current through the LED and thus its perceived brightness. To ensure that no detectable "flickering" occurs, the PWM frequency should be above 300 Hz in the process, in a range that is not perceptible to the human eye.

Current dimming and PWM can also be combined to make the most of the advantages of both methods.

The combination of direct and indirect lighting is often perceived as pleasant. For this purpose, luminaires with only direct light and with only indirect light can be used in the same room. Luminaires that combine direct and indirect light are an alternative. The light from these luminaires is predominantly indirect. It is directed to the viewer via ceilings and walls.

Direct lighting is when luminaires guide their light directly into the room and onto the surfaces where light is needed.

If individual (or several) parameters of the lighting change - e.g. the illuminance, the light color or the light direction - this is referred to as "dynamic lighting". This also includes color-dynamic light, such as from LEDs with RGB color mixing.

Since flicker and pulsation can cause fatigue and headaches, they pose an increased risk and increase the risk of accidents. The use of electronic ballasts (EBs) are now state of the art and provide a remedy. They not only save energy, but also reduce the flickering of light sources.

The term "floodlight" refers to powerful spotlights that are primarily used outdoors. The luminous intensity distribution of floodlights depends on the intended use: light for stadiums and sports fields or light for illuminating facades and objects.

Full spectrum lamps are rod-shaped three-band fluorescent lamps. Their light corresponds in spectral composition to daylight, which is why these lamps are often referred to as full-spectrum daylight fluorescent lamps. As a result, they also have a higher ultraviolet (UV) light content than normal fluorescent lamps. In full-spectrum lamps intended for general lighting, the UV content is reduced to protect against high radiation exposure. Because of the increased UV content in their light, full spectrum lamps are also used for medical therapeutic purposes. They allow the controlled use of UV radiation, which is known to cause harm in excess.

Glare can come directly from luminaires, lamps, or other surfaces that have excessive luminance (direct glare). Glare can also occur on shiny surfaces due to reflection (reflected glare). Both direct and reflected glare reduce visual comfort (psychological glare) and reduce visual performance (physiological glare).

Glare is dependent on

• Luminance and size of the light source
• Location of the light source relative to the observer
• Brightness of the environment and background

Glare can be minimized by proper placement and shielding of luminaires and selection of light colors and matte textures of room surfaces.

Direct glare can be avoided if luminaire surfaces have the lowest possible luminance levels at shallow angles and direct views into light sources are shielded. Direct glare is rated using the Unified Glare Rating (UGR) method; standards specify minimum glare control values. Appropriately positioned luminaires and workstations, light entering from the side, matte surfaces in the room and luminance limitation of luminaires prevent reflected glare.

In the "Human Centric Lighting" concept, biological aspects are given equal consideration alongside visual aspects of perception and visual comfort. Synonyms are "integrative lighting", "biologically effective lighting" and "melanopic effect of light on humans".

The illuminance E describes how much light (luminous flux) hits a surface. To calculate the illuminance E, the quotient of the luminous flux Φ and the illuminated area A is formed: E=Φ/A.

The illuminance is expressed in lumens per square meter, or lux (lx). In any virtual plane in the room, the illuminance can be calculated or measured with a luxmeter. The assessment surfaces are usually assumed to be horizontal, e.g. the desk. Vertical illuminance is important for shelf walls or face recognition, for example.

The illuminance does not describe the brightness impression of a room. This depends essentially on the reflective properties of the surfaces. With the same illuminance, a white-painted room appears brighter than a dark-painted room.

Indirect is the lighting when the luminaires direct their light, for example, on walls or ceilings, from where it is redirected to the viewer. The luminaire is shielded from the viewer, from glare by direct light emission. As a rule, indirect light is combined with direct light to create a pleasant atmosphere. Exclusively indirect light provides a diffuse spatial impression and a low-shadow lighting situation. To save energy, indirect lighting should be used in rooms with bright walls and ceilings.

LEDs can be found in almost all lighting applications today. The smallest electronic components that produce light efficiently, long-lasting and controllable: LEDs have revolutionized the lighting market.

Among their advantages:

• Low energy consumption
.
• Color stable
• Mostly maintenance-free
.
• Easy to control
• Long life
• No UV or IR radiation
• Robust to shock
• Emit little heat to the outside

LEDs can also be operated at low temperatures without loss of power. For this reason, they are ideal for outdoor use as well as in cold rooms.

LEDs (light emitting diodes) are electronic semiconductor components that emit light under voltage in the colors red, green, yellow or blue. With the aid of an additional internal luminescent layer, blue LEDs can also produce white light. White light can also be generated by RGB color mixing. In practice, almost all color temperatures - from 2,000 to 7,000 Kelvin - and very good color rendering values of Ra 90 can already be achieved with white LEDs. If uniform light colors of all LEDs in use are important for the user, narrow binning (sorting) is essential.

LEDs are operated at low voltage. As a rule, several diodes are combined on a board to form a module, in some cases already with drivers matched to them. However, these can also be housed externally in the luminaire or in the circuit.

LEDs are available in countless light colors and in all shades of white. Colored light and dynamic color sequences can be easily implemented in conjunction with a lighting control system. It is important to ensure good compatibility of the electronic components; if they do not "talk" to each other, this can lead to malfunctions. Due to their basic controllability, however, LEDs are highly recommended for biologically effective lighting that changes light color and brightness along the lines of daylight.

Always exorbitantly high luminous efficiencies of more than 200 lm/W are published. However, these are "laboratory values" that are not achievable in practical operation due to electrical, optical and, above all, thermal losses. The service life of LEDs is also significantly influenced by environmental factors: only good thermal management - i.e. good heat dissipation - can ensure high values.

Maximum efficiency and a long service life are key quality features of LED luminaires. Luminaire body, LED module, optics and control gear form a complete system and are optimally matched to each other in quality luminaires. In the design of LED luminaires, dissipation of the heat generated during LED operation is very important because excessively high operating or ambient temperatures significantly shorten the service life of LEDs. The efficient LED luminaires can be used for almost any type of lighting. Because LEDs are by nature direct-beam, nearly point light sources, diminutive LED luminaires can be used well wherever direct-beam light is required, such as in spotlights, car headlights, or facade lighting. Where more planar, diffuse light is required, frosted glass or plastic covers or even Spherolit lenses are used to diffuse the light. LED luminaires with different LED chips or modules can - with appropriate control systems or light management - vary in their spectral components and change in their color temperature (K). The irradiance (W/m²) can also be modified if desired.

LED modules and light engines offer outstanding efficiency and long life. LED modules typically consist of multiple LEDs mounted on a carrier and optics with wide distribution lenses and reflectors. LED modules are virtually maintenance-free and can be used in a variety of applications. They are continuously dimmable and easy to control, providing white and colored light with good color rendering.

Electronic ballasts for LEDs, called LED drivers, guarantee constant output values (current or voltage) and thus optimally supply the LED modules operated with them at any time during their service life.

The white light emitted by light sources appears in the so-called light color. It is characterized by the color temperature in Kelvin (K). Low color temperatures (e.g. below 2,700 K) describe warm, reddish-appearing light colors, such as those emitted by warm white LEDs. High color temperatures describe cool, bluish light colors, such as daylight at about 6,500 K on an overcast day.

Light sources are identified as.

• warm white (< 3300 K)
• neutral white (3300 to 5300 K)
• daylight white (> 5300 K)

Daylight white is colloquially also called cold white.

The light colors affect the room atmosphere: warm white light is usually perceived as comfortable, neutral white light rather than factual. Daylight white light indoors appears pale and dull at illuminance levels below about 700 lux. This evaluation of the lighting mood corresponds to the perception in Central Europe. Southern Europeans, who enjoy more sun, usually prefer daylight white light; in northern Europe, warm white light colors are almost exclusively common.

For biological effects, daylight white lighting is closest to natural daylight. Light from standard LEDs at 6,500 K is about 85% of the effect of daylight D65. Even higher color temperatures are generally perceived as rather unpleasant and unnatural if they are used as the sole light source. The light from light sources of the same light color may have different color rendering properties.

The luminaire light output ratio (LOR) describes the ratio of the luminous flux emitted by a luminaire to the luminous flux of the light sources used. For many LED luminaires, an LOR of 100% is often specified because the LED light source is permanently connected to the luminaire.

The luminaire luminous efficacy characterizes the efficiency of the entire system of luminaire and light sources. The measure of efficiency is calculated from the quotient of the luminous flux emitted by a luminaire in lumens (lm) and the previously absorbed power in watts (W). The higher the lumen/watt ratio, the better a luminaire converts the energy input into light.

The luminance L can be perceived by the eye. It determines the impression of brightness of a surface, which depends on color and material. Luminance is measured in candela per unit area (cd/m²), for illuminants mostly in cd/m². Luminance is used as a planning parameter in outdoor lighting. For completely diffusely reflecting surfaces indoors, the luminance in cd/m² can be calculated from the illuminance E in lux and the reflectance ρ.
L = (ρ x E)/π

Luminants are all electrical equipment used to generate light.

Luminous efficacy (abbreviation: η) is the measure of the efficiency of light sources. It indicates how much energy must be expended for a certain luminous flux and is specified in lumens per watt (lm/W). The higher this value, the more efficient the light source.

Some examples:

• Incandescent lamp: 10 lm/W
.
• Halogen lamp: 20 lm/W
• Energy-saving lamp: 60 lm/W
• Rod-shaped fluorescent lamp: 110 lm/W
• LED light source: 180 lm/W

Conventional incandescent lamps convert only about five percent of electricity into light; the rest is heat. They have therefore been withdrawn from the market. Halogen lamps produce their light somewhat more economically. Better luminous efficacy is achieved by discharge lamps, which also include energy-saving lamps and fluorescent lamps, and especially LEDs.

The luminous flux indicates how much light a light source emits in all directions. It characterizes the total light output and is measured in lumens (lm). The luminous flux is determined with special measuring instruments or by calculation. It is considered a measure of the total brightness of a light source as perceived by the human eye V (λ).

In the age of efficient LEDs, the lumen rating is increasingly replacing the wattage that used to be the measure of brightness for incandescent lamps. What counts for lighting design is the luminaire luminous flux, which - in contrast to lamp luminous flux - already takes into account losses caused by the luminaire design.

Knowing the luminous flux is not sufficient for calculating the light distribution in a lighting system; here, the distribution of the luminous flux per solid angle must be known. The luminous intensity (abbreviation: I) is therefore the part of the luminous flux that radiates in a specific direction. It is measured in candela (cd).

Lux and lumens are units of measurement for central photometric quantities. Illuminance is measured in lux (lx). It indicates how much light - or, to be more precise, how much luminous flux - falls on a specific surface. Measurements are taken with a luxmeter. In the office, for example, at least 500 lux illuminance is required for working at a desk.

The luminous flux is measured in the unit lumen (lm). It describes the power radiated by a light source in all directions in the visible range.

The "power consumption" (also "wattage" or "wattage") is the electrical power in watts (W) consumed by a light source or ballast. For low-pressure and high-pressure discharge lamps, the addition of the power and the power consumption of the ballast gives the system power or system power consumption.

The reflectance defines what percentage of the luminous flux falling on a surface is reflected. Bright surfaces have a high reflectance, dark surfaces a low reflectance. Here, the diffuse portion of the reflection is decisive and not the directional (specular) portion, which describes the "gloss" of the surface.

Some examples:

• White ceiling or wall reflect up to 85% of the light,
.
• bright wood paneling up to 50%,
• red brick up to 25%
• and a black floor 0%.

Conclusion: the darker a room is equipped, the more light is needed to achieve the same illuminance on the surface.

The service life of light sources is usually specified in hours. For LEDs, high-pressure discharge lamps, fluorescent and compact fluorescent lamps with plug-in base, the rated life applies.

The "Unified Glare Rating" (UGR) method was developed by the International Commission on Illumination CIE (Commission International de l'Eclairage) to standardize the assessment of glare worldwide. In contrast to the predecessor method, in which glare was assessed by the luminance of a single luminaire, the UGR method calculates the glare of the entire lighting system for a defined observer position. All luminaires of a lighting system and the brightness of walls and ceilings are taken into account.

Visual comfort describes the sense of well-being that people experience through the lighting in a room. Visual comfort arises in particular with regard to good color rendering and a harmonious distribution of brightness.

Disturbing visual comfort.

• too low luminance and lack of luminance differences, because they create a less stimulating light atmosphere,
.
• too high luminance differences, because the resulting constant adaptation fatigues,
.
• too high point luminance differences, because they can cause glare.

A lighting system that provides visual comfort should also meet all other quality criteria. For example, the light must not dazzle.

The color mixing of light sources of white light color, mostly warm white and daylight white, is used as white-white mixing mainly for adaptive lighting. Warm white light color contains a higher proportion of red, corresponding to morning and evening light. Daylight white light color contains a higher blue component - like midday light. By mixing the colors of white light sources, the lighting conditions of the course of the day can be simulated, whereby in particular the good color rendering properties of the light sources used are retained for all lighting scenes.

Since 2016, the former Display Screen Equipment Ordinance (German: Bildschirmarbeitsverordnung, BildscharbV) has been part of the Workplace Ordinance (German: Arbeitsstättenverordnung). It serves to protect health when working with computers. Section 6 in the annex to the Workplace Ordinance specifies the requirements for the lighting of a VDU workplace:

"The lighting must be appropriate to the nature of the work task and adapted to the eyesight of the employees; an appropriate contrast between the screen and the working environment must be ensured. The design of the VDU workstation and the layout and arrangement of the lighting shall avoid disturbing glare, reflections or mirroring on the VDU and other work equipment."

In order to prevent accidents, the lighting of a workplace must be adapted to the conditions. The legislator has therefore included the lighting of workplaces in the Workplace Ordinance (German: Arbeitsstättenverordnung, ArbStättV) and specified the requirements for various areas of application in the Workplace Regulations (German: Arbeitsstättenregeln, ASR).