Lighting Basics

Lighting Basics

Preventing intrusive light
As an option, the LensoFlex®2 modules can be equipped with a Back Light Control system.
This additional feature minimises light spill from the back of the luminaire to avoid intrusive light towards buildings.



Light distribution without Back Light Control

Light distribution with Back Light Control

Colour rendering relates to the way objects appear under a given light source. The measure is called the “colour rendering index” or CRI.
A low CRI indicates that objects may appear unnatural under the source, while a light with a high CRI rating will allow an object’s colours to appear more natural.
The maximum value of the CRI of a source is equal to 100. The higher the value, the better the colour rendering is.
Light sources providing a CRI over 80 are considered as excellent for colour recognition.

Colour-temperature-chromaticity-diagram A specification of the colour appearance of a light source, relating the colour to a reference source (Planckian radiator) heated to a particular temperature, measured in Kelvin.

The CIE chromaticity diagram shows the evolution of this Plankian radiator (also called a black body radiator) through the different colours of the diagram.
For instance, a light source that has a colour temperature of 6000K emits a cool white light, as shown on the diagram for the black body heated at 6000°K.

Constant Light Output (CLO) is a system to compensate for the depreciation of luminous flux and to avoid excess lighting at the beginning of the installation’s service life.

In fact, the luminous depreciation that takes place over time must be taken into account to ensure a predefined lighting level during the luminaire’s useful life.

Without remote management, this simply means increasing the initial power upon installation in order to make up for luminous depreciation. By precisely controlling luminous flux, one can control the energy necessary so as to reach the required level – no more, and no less – throughout the luminaire’s life.


Smart upgradability
Since LED technology is constantly evolving, Schréder has developed upgradable lighting solutions.

All Schréder luminaires already benefit from the latest developments in electronics, photometry, materials and of course, LEDs.
In addition, they are designed so that they can be easily adapted to house LEDs yet to come.
Both the photometric engine and the electronic assembly can be replaced at the end of the LEDs’ lifespan to take advantage of future technological developments.

This FutureProof concept by Schréder, highlights the desire to offer solutions that will last over time and that will adapt to technological changes.


For horizontal surfaces, the illuminance is calculated by describing the distance (d) between the light source and the calculation point by means of the vertical height (h) of the light source above the surface.

 In the diagram (right), h = d cos g  or d = h / cos

So  Horizontal illuminance  becomes  Horizontal illuminance

This is called the horizontal illuminance at the point.

Illuminance is the quantity of light, or luminous flux, falling on a unit area of a surface.
It is designated by the symbol E.
The unit is the lux (lx).
One lux equals one lumen per square metre (lm/m²).
The illuminance is independent of the direction from which the luminous flux reaches the surface.
Some practical examples of common lux levels are given below:

Summer, at noon, under a cloudless sky 100 000 lux
Street lighting 5 – 30 lux
Full moon, on a clear night 0.25 lux

The illuminance is measured by the instrument called illuminance meter or luxmeter. It uses a photocell that must be corrected by a special filter in order to match the V(λ) sensitivity curve of the human eye.


Schréder has specifically developed second generation LensoFlex®2 photometric engines for lighting spaces in a sustainable and efficient way, to generate savings both in terms of total cost of ownership and CO2 emissions.


The LensoFlex®2 builds on the flexibility offered by a selection of lenses. To perfectly meet the needs of each kind of place to be lit, Schréder has designed a large range of photometries.
This concept is based upon the addition principle of photometric distribution. Each LED is associated with a specific lens that generates the complete photometric distribution of the luminaire. It is the number of LEDs in combination with the driving current that determines the intensity level of the light distribution.
The LensoFlex®2 concept has been used by Schréder as a platform to build a state-of-the-art range of LED lighting solutions that provide significant energy savings and offer flexibility both in terms of performance and control while ensuring a long lifespan.

LED optic 5068 Symmetrical




LED optic 5098




LED optic 5068




LED optic 5102




LED optic 5096 Symmetrical




LED optic 5103




LED optic 5096




LED optic 5117




LED optic 5118




LED optic 5119




LED optic 5120




LED optic 5121



Luminance is the concept for the luminous intensity emitted per unit of area of a surface in a specific direction.
It measures the light as perceived by the human eye. The visibility of all surfaces and objects being in our field of vision is due to their luminance, while illuminance levels are in fact not perceived.
The unit is the candela per square metre (cd/m2).


Surfaces with different reflecting properties will have the same illuminance, but different luminance.
The main criterion requested by the standard for road lighting applications is the luminance of the road surface. The good knowledge of the light reflection characteristics of the road pavements is consequently of main importance for achieving an accurate lighting design.

Luminous-flux-Ulbrecht-SphereLuminous flux is the total quantity of light energy emitted per second by a light source.

It is designated by the symbol F and is expressed in lumens.

Luminous flux measurement of artificial light sources is carried out within a perfectly diffusing white sphere, called an Ulbricht sphere.

This equipment measures the total amount of lumens emitted by the tested light source by comparison with a calibrated lamp.

Luminous intensity is the concept for the concentration of light in a specific direction, radiated per second.
It is designated by the symbol I. The unit is the candela (cd).
The luminous intensity can be defined as:
The luminous flux in a certain direction, radiated per unit of solid angle.
1 candela = 1 lumen / steradian

Intensity is not a function of distance
The photometrical performances of a luminaire are derived from the luminaire’s measured luminous intensity distribution. These measurements of luminous intensity are carried out in specialised laboratories, using goniophotometers.

A selective dynamic lumen output allows the luminous intensity to be adjusted according to the traffic density.
Dimming profiles can be programmed to provide just a little light at night when it is quiet and more light during rush hour.
This is done in accordance with international lighting standards.


Spectral distribution represents the distribution of the energy radiated at different wavelengths in the visible part of the spectrum.
It can be defined for every type of light source.
For example, as illustrated below, the spectral distribution of a high-pressure sodium vapour lamp has the main part of energy radiated in yellow-orange colours while the spectral distribution of a metal halide lamp has its energy radiated in all parts of the spectrum resulting in white light emission.

Spectrum-Metal-Halide Spectrum-High-Pressure-Sodium
High-pressure sodium lamp Metal halide lamp

For long lasting performance

The thermal management of LEDs is crucial for a luminaire’s reliability.
Controlling the heat extraction is essential for ensuring that the LEDs last a long time to maximise effectiveness and maintain the luminous flux over time.
Schréder has developed a concept – ThermiX® – which is based on optimising several parameters for a good thermal management of the LEDs:

1. Direct conduction by minimising the path between the heat source and the outside
Thermix_141784S_1SCHR Thermix_2
2. Thermal compartmentalisation between the LEDs and the electronic control gear 3. Optimised design of the external heat exchange surface

The illumination at the same point P on a vertical facet oriented towards the light source can also be given in function of the height (h) of this source and of the incident angle (g) of the luminous intensity I.



And with Vertical-illuminance2
becomes: Vertical-illuminance3

Energy-Savings-VPOIn the past, to reach required lighting levels, there was no choice over the power of light sources employed as it was imposed by the manufacturer.

Without remote management, a lighting asset manager would, for example, have to use a 100W lamp to reach the lighting level, even if 85W would suffice.

With remote management, it is possible to vary the luminous intensity precisely so that it corresponds to the required level, without wasting energy.

Visible light may be defined as any radiation capable to act upon the retina of the human eye causing a visual sensation.
Each simple radiation differs from others by its frequency, i.e. its wavelength.
The representation of a radiation by its wavelength is generally accepted, because the wavelength can be measured with great accuracy.

The graphical representation of a spectrum of electromagnetic radiation is also based on wavelengths.
The visible part of the spectrum spans the relatively narrow range between 380nm and 780nm.
These limits represent experimentally obtained averages, because, in reality, they may vary from one individual to another.