Common Questions

Light is energy. It is part of the electromagnetic spectrum that includes radio waves, microwaves, X-rays, infrared, and ultraviolet. These are all forms of electromagnetic radiation, the difference being in the wavelength (and therefore energy level) of the radiation. Visible light is simply that: visible energy. It is electromagnetic energy in a range that our visual system is sensitive to and that gives us the sensation of sight. In contrast, although infrared radiation is also electromagnetic radiation, our eyes are not sensitive to it. We get no sensation of sight from infrared; instead, we perceive it as heat. As light is a form of energy it obeys physical laws that apply to energy, including the laws of thermodynamics. The f rst law of thermodynamics states that energy cannot be created or destroyed; it can only be transformed from one kind of energy into another. Light can be produced with heat, where an object becomes so hot that it radiates energy as light. Light can be produced by the transformation of chemical energy. Visible light can also be produced by the transformation of other kinds of electromagnetic energy, such as ultraviolet or microwave energy. There is evidence all around us of the energy embodied in light. Solar cells transform the energy in visible light to electrical energy; industrial laser cutters are used to cut intricate patterns in everything from delicate paper to the toughest steel plates. But the most ubiquitous transformation of light energy is found among plants. Plants use the power of visible light to convert carbon dioxide and water into food

(a process called photosynthesis). The human visual system converts light energy entering the eyes into chemical energy that is used to communicate the information received by the eye to the brain.

Parameters and terms


The lumen (lm) is an SI unit of luminous flux. It is a description of the quantity of light either produced by a source or received by a surface. 1 lumen is the quantity of luminous flux within a solid angle of this type of steradian emitted by a light source that has a luminous intensity of 1 candela.

Luminous flux
This is a measure of the total amount of light emitted by  a light source or received by a lit surface. The SI unit for luminous flux is the lumen. Luminous flux is not a simple measurement of an amount of electromagnetic energy: it is weighted to match the sensitivity of the human visual system to different wavelengths of visible light.

Where luminance relates to the light produced by a source or reflected by a surface, illuminance describes the light that falls on a surface. We do not see illuminance. What  we see is luminance—the light reflected by the surface. The light reflected will be a proportion of the illuminance A white surface that receives the same illuminance as a black surface will reflect more light and have a greater luminance (or, in visual terms, it will appear brighter).

LED Construction

In essence, an LED consists of a P–N junction, that is, a junction made of
P- and N-type semiconductor materials. A P-type material is one which has a defciency of electrons resulting from molecular bonding when forming a crystal. Tis electron defciency is described as electron vacancy or hole so that the P-type material has excess holes which can carry current and contribute to electrical conduction. Similarly, an N-type material has a surplus of electrons arising from its molecular bonding. Tese electrons move freely in the crystal serving as charge carriers. When P- and N-type materials are close together, electrons from N-side fll the holes in P-side, creating anelectrically neutral zone called the depletion region between the two sides. Tis electrical barrier is enlarged or reduced by applying a “reverse” or a “forward” external bias, respectively. Light is emitted in a forward biased diode when injected minority carriers (electrons in the P-region and holes in the N-region) recombine with each other. Light is generated in a narrow wavelength band due to current flowing under forward bias; it is of one color or monochromatic. Te wavelength of the light generated depends on the bandgap energy of the material in which the P–N junction is made.

LEDs are available in a wide variety of sizes, colors and power ratings and development is proceeding at a rapid rate. Whilst LEDs come in a variety of styles, Figure illustrates two common forms.

The Light of the Future

Light-emitting diodes are the shooting stars of lighting. Tiny and extremely efficient, they are revolutionizing the world of light – delivering a whole new quality of lighting, addressing an ever growing number of applications and saving a great deal of energy. LEDs are the light of the future and are conquering the realm of general lighting.

Whether indoors or out, decorative or functional – LEDs (light-emitting diodes) permit solutions today that would have been in conceivable even a few years ago. Starting out as a colored signal indicator, the energy-efficient semiconductors advanced rapidly to become one of the principal light sources for accent and orientation lighting. With white light and intelligent manage mint, LEDs now ensure a high quality of lighting right across the range of outdoor and indoor applications.

LED technology is regarded as the most important invention in the history of lighting since Edison’s development of the “lightbulb” over a hundred years ago. Never before has so much light come from such a small fitting; never before have light sources worked so reliably for so many years and consumed so little electricity. Even recently, attention still focused on the richness of colour achieved by LEDs; today, high-performance LEDs are transfiguring general lighting.

The many positive characteristics of the light-emitting diode include:

  •  extremely long life and virtual freedom from maintenance
  • high efficiency
  •  white and colored light with good color rendering properties
  • insensitivity to vibration
  • light with almost no heat generation, no IR or UV radiation, no interference with nocturnal insects
  • instant, flicker-free lighting that is infinitely
  • dimmable
  •  very compact design
  • no mercury content and no end-of-life
  • disposal problems.

What is the UGR value? When is it required and used?

The abbreviation UGR stands for »unified glare rating«. The UGR value is a dimensionless parameter which provides information about the degree of psychological glare of a lighting installation in an indoor space. UGR values are defined in steps within a scale of 10 to 30.  In DIN EN 12464-1:2011-08 the steps within this scale are 13, 16, 19, 22, 25 and 28. In the final instance these steps express the statistical perception of glare experienced by a large number of observers. So UGR 19, for example, means that 65% of observers »did not really feel disturbed« by the glare. Conversely, of course, this also means that the remaining 35% felt disturbed by the glare. The lower the UGR value, the less direct glare is experienced by the observers.

The UGR value can only be calculated; it cannot however be directly determined photometrically. Where there are lighting installations with luminaires from which 65% of the light is emitted indirectly and where narrow beam spots or asymmetrically radiating luminaires are installed, then, by definition, it is not possible to indicate a UGR value.

Contrary to widespread opinion the UGR value is not really a property of a luminaire. Here we are dealing with much more than the interaction of the »brightness level« of the luminous surfaces of a luminaire in relation to the »brightness level« of the surroundings and the position and viewing angle of the observer. The average »brightness« of the light emitting surface of a luminaire is defined in this context as the average luminance of the luminaire and the »brightness« of the background or the surroundings as background luminance.

The following example taken from a real-life situation demonstrates clearly the influence which the ratio of these brightness levels to each other can have on the glare effect: Imagine that you are driving along a road at night with no street lighting. A car now comes towards you with headlights on full beam. You are blinded by the strong light and are hardly able to keep your eyes on the road. Imagine the same situation on a sunny summer’s day. The same vehicle approaches again with the headlights on full beam. Now you are far less likely to be blinded by the headlights. Yet the properties of the headlights have not changed at all. The degree of direct glare results here mainly from the contrast to the surroundings (i.e. the background luminance).

The position and the viewing angle of the observer also have to be borne in mind. For, if the luminaire is not in the field of vision of a person, then this same person cannot be affected by glare. In certain norms, depending on the field of activity, adherence to UGR thresholds is required. These can be found in the current DIN EN 12464-1:2011-08 under »5 Index of Lighting Requirements«. Since the issue here is maximum UGR thresholds, the term UGRL (Unified Glare Rating Limit) is used. In accordance with DIN EN 12464-1:2011-08 the lighting designer must provide evidence of the direct glare categorization with the aid of the tables of the CIE Unified Glare Rating method (acc. to CIE 117-1995). The purpose of the tabular method is to make it easier for the lighting designer to apply the very complex formula behind the UGR value.

Limitations of the tabular method when determining the UGR value

The lifetime of a lamp is usually specified in
hours. For LEDs, high-pressure discharge lamps as well as fluorescent and compact fluorescent lamps with plug-in base it is given as the rated lifetime. All these light sources degrade, i.e. their brightness diminishes with operation. The rated lifetime (given as L) therefore describes the time in which the luminous flux of the light source falls to the specified value. For general lighting, typical values are L80 or L70. Thus the average rated lifetime of an LED is reached when the luminous flux reaches 70 percent of its value at installation.
The degradation and failure of LEDs is determined essentially by the let-through current and the temperature inside the LED; in
the case of modules, the electrical wiring of
the LED, the ambient and operating temperature and further module characteristics also play a role.

The color temperature of a light source is the temperature of an ideal black-body radiator that radiates
light of a color comparable to that of the light source. Color temperature is a characteristic of visible
light that has important applications
in lighting, photography, videography, publishing, manufacturing, astrophysics, horticulture, and other
fields. In practice, color temperature is meaningful only for light sources that do in fact correspond
somewhat closely to the radiation of some black body, i.e., those on a line from reddish/orange via
yellow and more or less white to blueish white; it does not make sense to speak of the color
temperature of, e.g., a green or a purple light. Color temperature is conventionally expressed in kelvin,
using the symbol K, a unit of measure for absolute temperature.
Color temperatures over 5000 K are called "cool colors" (bluish white), while lower color temperatures
(2700–3000 K) are called "warm colors" (yellowish white through red). "Warm" in this context is an
analogy to radiated heat flux of traditional incandescent lighting rather than temperature. The spectral
peak of warm-colored light is closer to infrared, and most natural warm-colored light sources emit
significant infrared radiation. The fact that "warm" lighting in this sense actually has a "cooler" color
temperature often leads to confusion.







Zone 0

must be SELV (Separated Extra Low Voltage max. 12Volts) and have a minimum rating of IP67.

Zone 1 The recommended IP rating for lights in this area is IP65.

Zone 2 A minimum IP rating of IP44 is required in this zone.

Zone 3 (outside zones)

Zone 3 refers to anywhere outside of zones 0, 1, and 2. There is no need to use IP rated fittings in this zone however if there is any chance of a direct water jet being used for cleaning purposes in zones 1, 2 and 3 a fitting rated a minimum of IP65 must be used. It is also sensible to apply an element of common sense.  If a light fitting is within a steamy bathroom but just outside of zone 2, for example, consider if an IP44 light fitting may be more appropriate.

Zone 0

must be SELV (Separated Extra Low Voltage max. 12Volts) and have a minimum rating of IP67.

Zone 1 The recommended IP rating for lights in this area is IP65.

Zone 2 A minimum IP rating of IP44 is required in this zone.

Zone 3 (outside zones)

Zone 3 refers to anywhere outside of zones 0, 1, and 2. There is no need to use IP rated fittings in this zone however if there is any chance of a direct water jet being used for cleaning purposes in zones 1, 2 and 3 a fitting rated a minimum of IP65 must be used. It is also sensible to apply an element of common sense.  If a light fitting is within a steamy bathroom but just outside of zone 2, for example, consider if an IP44 light fitting may be more appropriate.

Class I
Luminaires in this class are electrically insulated and provided
with a connection to earth. Earthing protects exposed metal
parts that could become live in the event of basic insulation

Class II
Luminaires in this class are designed and constructed so
that protection against electric shock does not rely on basic
insulation only. This can be achieved by means of reinforced or
double insulation. No provision for earthing is provided.

Class III
Here protection against electric shock relies on supply at Safety
Extra – Low Voltage (SELV) and in which voltages higher than
those of SELV are not generated (max. 50V ac rms).

Many interior lighting luminaires are made from ready-painted sheet steel, white being the
usual paint colour. Where corrosion is a problem, galvanised sheet steel is used. Where a very
durable paint finish is required, enamelling is used.

Aluminium sheet
Aluminium sheet is mainly used for reflectors in luminaires. It can have good reflection
properties and the physical strength to form stable reflectors of the desired form.

Cast aluminium
Cast aluminium is widely used for floodlight housings. Such housings are light in weight and
can be used in damp or corrosive atmospheres without any further treatment provided that the
correct grade of aluminium has been used.

Three types of glass are used in luminaires; soda lime glass, borosilicate glass, and very high
resistance glass. Soda lime glass is used where there are no special heat resistance demands.
Where high heat resistance, chemical stability and resistance to heat shock are required,
borosilicate glass is used. High resistance glass has the advantage that it can deliver high heat
resistance, high thermal shock resistance and great physical strength even in thin sheets.

Stainless steel
Stainless steel is rarely used for luminaire bodies but it is widely used for many small,
unpainted luminaire components that have to remain free from corrosion.

There are many different forms of plastic used in luminaires, either for complete housings or
components. These plastics differ in their transparency, strength, toughness, sensitivity to UV
radiation and heat resistance.

Optical control of the light output from a light source is achieved by some combination of
reflectors, refractors, diffusers, baffles or filters.
Three types of reflector are used in luminaires; specular, spread and diffuse.
Specular reflectors are used when a precise light distribution is required. The shape of the
reflector and its position relative to the light source determine the light distribution. The most
common shapes for reflectors are circular, parabolic and elliptical.
A circular reflector with a point light source at its focus will produce a light distribution of the
Type , reflections from some parts of the reflector being almost parallel
while those from parts of the reflector away from the axis are divergent

A parabolic reflector with a point light source at its focus produces a parallel beam of reflected
light, Moving the light source in front or behind the point of focus will cause the
beam to converge or diverge. The parabolic reflector is widely used in spotlight design either
exactly, when the reflector is smooth, or approximately, when the reflector is facetted .

An elliptical reflector with a point light source at one focus will ensure that the reflected rays all
pass through the second focus . Such reflectors are used in applications which
need medium-wide to wide LIDC.

Typical reflectance values for materials used in reflectors


Diffusers are transparent materials that scatter light in all directions. They do serve to reduce the brightness of the luminaire. Diffusers are commonly made of materials that maximise light scatter and minimise absorption, such as
opal glass or plastic.

Opal diffuser – creates cosine LIDC by scattering of a light on microparticles which are evenly distributed in basic
diffuser material.

Prismatic respectively micro-prismatic diffuser – basically these are refractors.
Geometric structures such as pyramids, hexagons, spherical domes, and triangular ridges create requested LIDC using the refraction law. They are used in luminaires where high lighting quality is requested (UGR – Unifed Glare Ratio; Lavg – average luminance of the luminaire)

The European standard EN 50102 dated March 1995 defines a coding system
(IK code) for indicating the degree of protection provided by electrical equipment

Example   Ik 08

The motion detected by 1 sensor (the master unit) can pass onto other pre-dened individuals (the slave units) though RF transmission. The master can trigger unlimited number of slaves as long as within the transmission range.

Typical Applications

For staircase

For carpark


Luminaires with built in corridor function are a very simple and highly effcient way of reducing energy consumption. Wherever light has to be provided 24 hours a day for statutory reasons, the corridor function helps provide the right light, combined with energy-effcient and cost-effective operation. This economical form of 24-hour lighting is ideal .

It offers 3 levels of light:100%–>dimmed light (10%, 20%, 30%, 50% optional)–>off; and 2 periods of selectable waiting time: motion hold-time and stand-by period; selectable daylight threshold and freedom of detection area.

Two common ways of generating white light with LEDs are
1) convert short wavelength optical radiation with a down-conversion phosphor to create a broad emitting SPD
2) combine multiple narrow-band LEDs using additive color mixing.
convert short wavelength is most widely used at present is based on the luminescence conversion principle used for fluorescent lamps: a very thin film of yellow phosphor material is applied to a blue LED chip, which changes part of its blue light into white. To achieve the light color required, the concentration and chemical composition of the phosphor material needs to be very precisely controlled. Today, a variety of white tones are possible, from warm white (color temperature 2,700 kelvin, K) through neutral white (3,300 K) to daylight white (5,300K). Other advantages of this method include relatively high luminous fluxes and good color rendering up to Ra 90.

combine multiple narrow-band LEDs is to mix colored light of different wavelengths (red, green and blue). This method has the advantage of permitting controlled changes of light color, allowing not just white but also colored light to be produced. So RGB solutions are good for dynamic colored lighting applications. Realizing white light by this method also calls for a great deal of expertise because precise control is difficult to achieve with colored LEDs of different brightness and results in white light with a poorer color rendering property – Ra  70 to 80 – than that produced by luminescence conversion. Where white light is required to permit a switch from warm white to cool white for office applications, for example, new technologies combine colored chips with white LEDs. The result is dynamically changing white light with a good color rendering property.

Historical information
In the study of color perception, the first question that usually comes to mind is “what color is it?”. In other words, we wish to develop a method of specifying a particular color which allows us to differentiate it from all other colors. It has been found that three quantities are needed to specify a particular color. The relative amounts of red, green and blue in a color will serve to specify that color completely. This question was first approached by a number of researchers in the 1930s, and their results were formalized in the specification of the CIE XYZ color space.
The second question we might ask, given two colors, is “how different are these two colors?” Just as the first question was answered by developing a color space in which three numbers specified a particular color, we are now asking effectively, how far apart these two colors are. This particular question was considered by researchers dating back to Helmholtz and Schrödinger, and later in industrial applications, but experiments by Wright and Pitt, and David Mac-Adam provided much-needed empirical support.

Mac-Adam set up an experiment in which a trained observer viewed two different colors, at a fixed luminance of about 48 cd/m2. One of the colors (the “test” color) was fixed, but the other was adjustable by the observer, and the observer was asked to adjust that color until it matched the test color. This match was, of course, not perfect, since the human eye, like any other instrument, has limited accuracy. It was found by Mac-Adam, however, that all of the matches made by the observer fell into an ellipse on the CIE 1931 chromaticity diagram. The measurements were made at 25 points on the chromaticity diagram, and it was found that the size and orientation of the ellipses on the diagram varied widely depending on the test color. These 25 ellipses measured by MacAdam, for a particular observer are shown on the chromaticity diagram above.

LED Color Difference SDCM & MacAdam Ellipses

SDCM is an acronym which stands for Standard Deviation Color Matching. SDCM has the same meaning as a “MacAdam ellipse”. A 1-step MacAdam ellipse defines a zone in the CIE 1931 2 deg (xy) color space within which the human eye cannot discern color difference. Most LEDs are binned at the 4-7 step level; in other words, you certainly can see color differences in LEDs that are ostensibly the same color.

Due to the variable nature of the color produced by white light LEDs, a convenient metric for expressing the extent of the color difference within a batch (or bin) or LEDs is the number of SDCM (MacAdam) ellipses steps in the CIE color space that the LEDs fall into. If the chromaticity coordinates of a set of LEDs all fall within 1 SDCM (or a “1-step MacAdam ellipse”), most people would fail to see any difference in color. If the color variation is such that the variation in chromaticity extends to a zone that is twice as big (2 SDCM or a 2-step MacAdam ellipse), you will start to see some colour difference. A 2-step MacAdam ellipse is better than a 3-step zone, and so on.

It should be noted that SDCM ellipses are often shown in the CIE colour space diagram at a ten times magnification (see image to left) because they would otherwise be too small to be seen clearly when viewed in the complete CIE diagram.
MacAdam’s experiments demonstrated that the size of an SDCM ellipse is quite small, which means that the human vision system is very good at discriminating colour differences when viewing two light sources at the same time. If we consider the size of the 1-step SDCM ellipse at an arbitrary 3,000K colour temperature, the CCT range is ±30K, and the corresponding u’v’ range (the chromaticity coordinates in the 1976 CIE Uniform Colour Space) is ±0.001. In other words, if we view two LEDs with a CCT difference of more than 60K, the chances are that we will see a colour difference.
The table below relates the number of SDCM ellipse steps to the range of CCT and chromaticity coordinates for a 3000K colour temperature light source.

Within the lighting industry, reference is often made to the standard IES LM-79-08 “Approved Method of Electrical & Photometric Measurements of Solid State Lighting Products” published by the Illuminating Engineering Society of North America (IESNA). This in turn references the American standard ANSI C78.377-2008 “Specification for the Chromaticity of Solid State Lighting Products” which places white light LEDs used for illumination into standard colour groups which all have the same “nominal” correlated colour temperatures (CCTs). The size of the ANSI C78.377 nominal CCT quadrangle is a 7-step MacAdam ellipse. A 7 to 8-step SDCM is currently representative of the variation in chromaticity of high brightness white LEDs used for illumination.

A perfect LED module assembly line will produce batches of modules operating within a once MacAdam Ellipse. There will be no discernible difference between any of the module outputs. LED modules produced at this level are used where colour performance and accuracy between fixtures is vitally important. Typically, good LED modules are produced within a two to three MacAdam ellipse range, here will be a visual difference if you look for it, but it is minor and generally considered to be acceptable in commercial usage.
Cheaper products will often use LED modules that have a range of MacAdam Ellipses beyond four, some going as high as eight. Fixtures using such modules need to be used with care. There may be general commercial of industrial areas where they are acceptable, but any requirement for colour sensitivity would rule them out
So when an LED supplier proudly claims to offer you LEDs binned to a 4-step MacAdam ellipse tolerance (or 4xSDCM), keep in mind that this is better than LEDs that are binned to 5-steps but you will still see a colour difference over the range of LEDs supplied to that specification.

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