OVERVIEW OF BASIC TERMS
IN LIGHTING TECHNOLOGY

BASIC LIGHTING TERMS AND THEIR MEANING

Consumers often come across basic lighting terminology when buying light sources. But if you don’t know what these terms mean, how can you make the right choice? We shed some light on the matter and explain the most important basic lighting terms in a clear and concise manner.

There are so many different types of light sources – but which one is right for me?

BASIC CONCEPTS IN LIGHTING TECHNOLOGY 

1. LUMINOUS
   FLUX Unit: Lumen (lm) = Luminous intensity
   The luminous flux Φ denotes the total light output of a light source in all directions and takes into account the human eye’s perception of brightness. Nowadays, lumens are the standard unit of measurement for the light output of all light sources.
   
   What used to be the good old WATT rating is now lumens. This figure is actually much more accurate, as it indicates how much light is ACTUALLY emitted by a light source. The wattage of modern LED light sources is significantly lower; after all, they are much more economical and efficient. Nevertheless, the equivalent wattage is also often found on the packaging of many LEDs to make conversion easy and clear!
   
   
2.  LUMINOUS EFFICIENCY
   Unit: lm/watt
   Luminous efficiency η denotes the ratio of luminous flux to electrical power consumed. It therefore provides an initial indication of a light source’s energy efficiency. 
   
   
3.  LUMINOUS INTENSITY
   Unit: candela (cd)
   Luminous intensity I refers to the amount of light emitted by a light source in a specific direction. It is also defined as luminous flux per solid angle. 
   
   
4.  LUMINANCE
   Unit: cd/m²
   Luminance L is a measure of the perceived brightness to the human eye. It is produced by self-luminous or illuminated surfaces. The luminance of an illuminated surface depends heavily on its reflectance.

Basic concepts of lighting technology, luminous flux, luminous intensity, illuminance, luminance

5.  ILLUMINANCE
   Unit: Lux (lx)
   Illuminance E indicates the luminous flux falling on a defined area from a light source. It is often used to determine the positioning and sizing of interior lighting.
   
   
6. THE COEFFICIENT OF REFLECTION
   Unit: %
   The coefficient of reflection ρ depends on the color and texture of a surface and indicates the proportion of incident light that is reflected. The lighter and smoother the surface, the higher the coefficient of reflection. For white ceilings and walls, the coefficient of reflection can be as high as 90%.
   
   
7. LIGHT COLOR
   The color of light plays a decisive role in determining a room’s atmosphere. This is primarily determined by the color temperature of the light source. It is measured in Kelvin (K) and ranges from ‘warm white’ (below 3500K) through ‘neutral white’ (3500K – 5300K) to ‘daylight white’ (over 5300K).
   
   Depending on the color temperature, lighting has different characteristics and effects on people. From cosy, warm and relaxing to stimulating and invigorating. Our internal clock plays a major role here. You can read about which color of light is most suitable for which purposes and where they are best used here in the knowledge database.

Basic concepts in lighting: color of light, color temperature

8.  COLOR RENDERING
   The color rendering index (Ra), also known as CRI (Color Rendering Index), indicates the extent to which colors are accurately reproduced under artificial lighting. The CRI depends primarily on the spectral composition of the light source, i.e. on the type and quality of the filaments and materials used.
   
   In some areas, the color rendering properties of lighting play a major role, e.g. in retail spaces, restaurants, etc. Sunlight and incandescent bulbs, with their uniform full spectrum, achieve a CRI (Color Rendering Index) of 100, which means that all spectral colors are present in equal distribution and objects are rendered in their correct colors naturally. However, LED light sources do not have a continuous spectrum and do not reach the maximum value. With many technical refinements and tricks, however, they can come close. The higher the specified value, the better the color rendering of the illuminated object. Therefore, if natural color rendering plays a particularly important role, high-quality LED light sources with a CRI of at least 85 should be purchased.
   
   
9. THE POWER FACTOR
   The power factor refers to the ratio between the actual power and the apparent power of an electrical appliance. It always ranges between 0 and 1, with 1 being the ideal case. Above all, the power factor says a great deal about the quality of an electrical circuit, indicating whether it consumes unnecessary power or not.
   
   

MARKINGS AND CERTIFICATION MARKS

1. THE CE MARK
   Stands for: Communauté Européenne (European Community)
   The CE mark is a prerequisite for the sale of a product within the EU. By affixing it, manufacturers and retailers confirm on their own responsibility that the ‘essential requirements’ have been met. This is done without the involvement of an independent testing body.
   
   
2. THE GS TEST MARK With this mark, authorised testing bodies certify a product as having
   “tested safety”. It must comply with the Equipment and Production Safety Act and the relevant EU directive. The test mark covers the safety testing of a device, but also, for example, the completeness of the operating instructions. Testing bodies in this context include, for example, TÜV and VDE.
   
   
3. ENEC / VDE TEST MARK
   ENEC: EN – European Standards, EC – Electrical Certification, also in combination with the VDE mark (Association of German Electrical Engineers).
   
   Products bearing this mark generally comply with the current state of the art in technology and safety and thus with the GPSG (Equipment and Product Safety Act). Furthermore, the VDE also monitors the production of electrical appliances.
   
   
4. IP PROTECTION
   RATINGS The IP protection rating indicates the suitability of electrical appliances for different environmental conditions. The two digits represent 1. resistance to solid objects/dust and 2. protection against water/moisture.

Source: www.licht.de

5. PROTECTION CLASSES
   The protection class indicates the level of protection lamps offer against electric shock or short circuits. There are three classes.
   
   Class I – features an earth connection. All metal parts that can be touched externally must be connected to an external protective conductor. This safely diverts any fault current.
   
   Class II – features double protective insulation. This double insulation is often found in cables with a Euro plug.
   
   III – refers to devices operated on safety extra-low voltage, i.e. using batteries, rechargeable batteries or solar energy. This is below 50 volts. In this class, no protective conductor may be installed.

Left: Protection class 1; Centre: Protection class 2; Right: Protection class 3

We have now explained the key basics of lighting technology. For some of these topics, there are more detailed articles available to read, helping you to understand and learn more. This way, nothing can go wrong when buying light sources and luminaires!