Light color - Kelvin

Does white light have a color? No, it is a multicolored light and therefore white. But we know differences of white light. Fluorescent is commonly known to us as cold white light, however, incandescent light is known as warm white light.
LEDs offer a wide range of white light colors. You can choose from warm white like incandescent lamps to cool white like polar sunlight.

 3 main groups of luminaires are typical:

  • warm white = ca. 2000-3200 Kelvin
  • neutral white = ca. 3300-5300 Kelvin
  • cool white = 5300 and> Kelvin

In order to establish standardized values, physics has devised a theoretical black spotlight that changes its color from red-yellow to white and blue when heated. A scale has been derived from this, which is used as the unit of measurement Kelvin (K).

A draft flame image gives us a simple idea for the color temperature. At a lower temperature it is yellowish red, at a higher temperature it becomes bright white to slightly bluish.

Color rendering index (CRI) Ra

CRI is an abbreviation for "Color Rendering Index" and means a color rendering index, which is given in Ra.

Color rendering describes the relationship between the color stimulus and the color impression.It is therefore a matter of reproducing the colors of objects that are illuminated with different light sources and then compared with a reference light source. On the one hand, a black spotlight with a color temperature of up to 5,000 Kelvin and, on the other hand, a light with a spectrum similar to daylight over 5,000 Kelvin serves as a reference.
A Ra 100 is the best color reproduction = no deviation from the ideal template, the colors of the illuminated object appear as in nature.
In work areas such as offices only lamps with a color rendering index of at least Ra 80 should be used. All rooms in which color perception is important need the highest possible color rendering index (i.e. Ra 90 upwards).

With fluorescent lamps, the Ra value is often encoded on the lamp.

The printed value 850 means a Ra value of at least 80 (850) with a color temperature of 5000 Kelvin (850)

Luminous flux

The total luminous flux, or better understood the entire amount of light emitted from a light source, whether of round emitters such as incandescent lamps, fluorescent lights, or halogen lamps, is expressed in lumens.

Thus, this size is the only comparison metric for better or worse bulbs.
But if you look for the energy efficiency of a light bulb, then "lumens to watts" is important.


In light emitters such as halogen lamp or reflector lamps, the axial luminous intensity in candelas is often given.
This value is important where all that matters is brightness in the center of the emitted light cone and not to speak in an efficient lighting of the room.
An example of this is a punctual highlight of goods in a bottom-lit store. Also inefficient LED Spotlight (lumens / watt) can generate high candela values when the light is strongly directed to the axis.


The illuminance in lux (lx) is the quotient of the luminous intensity of a point source of light in candelas (cd) and the square of the distance in meters (m). Thus, the illuminance gets a quick reference when a single light source is considered such. As with artificial lighting. Conversely, the brightness outdoors has virtually nothing to do with distances, since the light source is practically infinite (for example, cloud cover).
The light intensity is measured with the lux meter or calculated in simulations such. As to determine whether a work surface is sufficiently illuminated. You can find instructions in countries Committee on Occupational Safety and Health (LASI).

Beam angle

The light beam angle of a lamp can be seen clearly with the naked eye only focus lamps. There, the clearly defined beam of light is unique. For all other lamps and lamps as the eye can only distinguish general and in very strong dependence on the ambient light of the observation space. The beam angle describes only a guideline for many LEDs. If the LED has an internal or external optical enlargement or alteration, the beam angle can differ considerably.
Where a plurality of light bulbs built close to each other, the light at places where overlap several circles of light could be particularly intense. LEDs without optics stem are therefore better suited for such bulbs. As this intense light the center and the edge leaves the light intensity according to uniform. LED bulb with a higher luminosity as power LEDs or LED hight lumen compared to standard incandescent lamps or LEDs - generate a very strong light.

What is a lumen to watt?

The light output of a lamp is measured in lumens. Under light flux is defined as the total in all directions from the light source in the room emitted visible light. Watt electric power and has served as a parameter for the power consumption of a lamp. This has changed with the energy efficiency of new bulbs. The sale of the luminous flux for all lamps is specified as a parameter, in addition to the first wattage. The lumen on the package is rule in the european Union since 01 September 2010. The lumen value shows the comparison of lamps.
As a replacement for a 15 watt incandescent light (136 lumens) an LED bulb with about 3 watts is recommended. Now, since the number of lumens must be stated that the consumer can orient it even now. This ensures that the LED lamp is as bright as the incandescent lamp replaced.