Leds and other artificial light sources

In technical terminology, lamps are the illuminant, i.e. the part of a luminaire that produces the light.

Light fixture

A light fixture is the entire system in which one or more lamps are built in (e.g., a light fixture).B. ceiling light, floor lamp). Colloquially, lights are often called lamps.

No one would want to do without artificial light sources – be they energy-saving lamps (compact fluorescent lamps), halogen lamps, incandescent lamps or LEDs (light-emitting diodes) – in everyday life.

"Why don’t you turn on the light?"

We flip a switch or push a button and there it is, the light that illuminates our living and working environments. But how does it work?

Incandescent lamps and halogen lamps

Incandescent lamps and halogen lamps are so-called temperature radiators. Light is produced by heating a metal wire and causing it to glow. However, most of the supplied energy is lost as heat. This makes this type of lamp inefficient.

Fluorescent lamps

Fluorescent lamps are available in tube form (fluorescent tube) or "coiled", so to speak as compact fluorescent lamps (energy-saving lamps). When the lamp is switched on, a gas inside it is excited. This excitation produces UV radiation. Fluorescent materials applied to the inside of the lamp tube then turn the high-energy UV radiation into lower-energy, visible "white" light Light.

Light emitting diodes (LEDs)

LEDs are comparatively new on the market. Their market share is increasing, not least because of energy efficiency requirements and their versatility. LEDs are small semiconductor devices. Since they basically produce almost monochromatic (i.e. z.B. blue, yellow, red) light, tricks have to be used to produce white light, which is composed of a mixture of different wavelengths.

1. Photoluminescence

2. Additive color mixing

In this case, white light is produced by combining single-color red, green and blue LEDs. By selectively controlling the individual LEDs, colored light can be produced in addition to white light. This process is used, for example, in televisions, where LEDs are used for image display and backlighting, or for stage lighting. It is not common for mass-produced products such as household lamps.

Spectra of artificial light sources

The spectrum of a light source shows what proportion the different colors (wavelengths) make up of the emitted "white" light light, for example how high the proportion of high-energy violet and blue light is. How wavelength and color are related is explained in the article What is visible light?? shown.

Fig. 1 Comparison of the spectra of different lamps with the same color temperature 2700 Kelvin = warm white. LED (colored background), incandescent lamp (gray line), compact fluorescent lamp (dashed black line). Source: BfS

The diversity of LEDs is reflected in the spectra. The blue light component of LEDs can be higher or lower (see Figure 2).

Fig. 2 spectra of commercially available LED lamps for general lighting with different color temperatures. 2700 K (warm white, colored background), 3000 K (warm white), 4000 K (neutral white) and 6000 K (daylight white, also called "cool white"). Source: BfS

Basically, the higher the color temperature in Kelvin (K), the higher the blue light component. If you want to keep the blue light content lower, you can choose a lamp with warm white light (see recommendations for good lighting). Information on the effects of blue light and other effects of visible light can be found in the article Effects of light.

Safety of lamps and lamp systems

The photobiological safety of lamps and lamp systems is the responsibility of the manufacturers. When assessing safety, manufacturers usually refer to relevant standards. Not only the effects of visible light are considered, but also possible risks from UV radiation or heat radiation (infrared).
For more information on the photobiological safety of lamps and lamp systems and on classification into risk groups, see the article Protection in visible light.

Light flicker ("flicker")

One characteristic of artificial light sources that can be perceived as unpleasant is "light flicker". This is understood to mean fluctuations in the brightness of the light. The main cause of these variations is the fact that artificial light sources are operated with alternating current. If the current strength changes, as is the case with alternating current at a frequency of 50 Hz, the brightness changes 100 times per second.

Unlike incandescent lamps, compact fluorescent lamps and LEDs react quickly to these fluctuations in current intensity. which can make itself felt as flickering. Flickering can be consciously perceived up to a maximum of 100 Hz. Above this frequency, the eye can no longer resolve the changes in brightness and the light is perceived as uniform. However, there are also reports of complaints such as headaches or eye pain above this so-called flicker fusion frequency. To avoid flickering, a ballast must be used to ensure that the light source is constantly supplied with power for a short period of time. How well this succeeds is not least a question of quality.

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