Category Archives: L


Luminance is a photometric measure of the luminous intensity (brightness) per unit area of light travelling in a given direction. It describes the amount of light that passes through, is emitted from, or is reflected from a particular area, and falls within a given solid angle. The standard unit of luminance is candela per square meter (cd/m2).

Luminous intensity distribution curve

The luminous intensity distribution curve (LID) or light distribution curve is a graphical representation of the measured luminous intensity of a luminaire. In a LID, the luminous intensity in candela (cd) as well as the beam angle can be read.

Luminous efficacy

The luminous efficacy of a light source is its efficiency or energy efficiency, which is the quotient of luminous flux (lumen) and absorbed electrical power (watt). Thus, a 100 W light bulb that delivers a luminous flux of 1500 lm has a luminous efficacy of 15 lm/W. This means that only part of the electrical power absorbed by a light bulb is converted into visible light radiation. The remaining power is mainly emitted in the infrared range and is thus detectable as thermal radiation.

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Lumen (lm) is the internationally standardized unit of measurement for the luminous flux of a light source and thus allows conclusions to be drawn about the brightness of the illuminant. Colloquially, one also speaks of the light output of a lamp.

The luminous flux indicates the amount of light generated per unit of time; the unit of time is quasi = 0 due to the speed of light of 300,000 km/second, since the speed of light forms our perceptual limit.

Lumen is not to be confused with the unit for illuminance lux, which indicates how much light per unit of time is incident on a unit of area, i.e. the amount of brightness on/at an illuminated surface.


Lux (lx) is the internationally standardized physical unit of measurement for the illuminance of a light source. The name is derived from the Latin word for light.

The unit lux is calculated from the luminous flux incident on a given surface, i.e. the number of lumens per m². Thus, the illuminance of one lux corresponds to the uniform illumination of a 1 m² surface with a luminous flux of one lumen (1 lux is 1 lumen/m²). Alternatively, 1 lux can be defined as the illuminance at 1 meter from a point light source of luminous intensity 1 candela (1 cd).

Thus, the lux number depends on the distance between the light source and the surface: The greater the distance, the lower the number of lux.

Unlike lumen and candela, which are transmit quantities, lux is a receive quantity.


LPI is an abbreviation for „lines per inch“.

Similar to DPI or PPI, LPI Lines per inch (LPI) is a measurement of printing resolution. A line consists of halftones built up by physical ink dots made by the printer device to create different tones. Specifically LPI is a measure of how close together the lines in a halftone grid are. The quality of printer device or screen determines how high the LPI will be. High LPI indicates greater detail and sharpness.

Conversion of the LPI to DPI can be done by simple multiplication: z.B. 150 LPI x 16 = 2400 DPI

Light spectrum

The light spectrum is the visible range of the electromagnetic spectrum that can be perceived by the eye. The spectral range visible to humans is between 380 and 780 nanometers, corresponding to a frequency range of about 4·1014 to 7.5·10 14 Hz.

Each wavelength produces a different color, for example green has a wavelength of about 540nm and blue is between 450 and 500nm. If all visible wavelengths are displayed next to each other, a rainbow-like color gradient appears. In addition, there are wavelength ranges that the human eye cannot see or perceive because there is no trigger for a pulse. These ranges are called ultra-violet (10-380nm) and infrared radiation (>780nm). The shorter a wavelength is, the more energy it has. This is also the reason why ultraviolet light is so harmful for our skin and our eyes, because in the long run it stimulates molecules to change their spatial structure and to split off single atoms.

Line sensor

Line sensors are light or radiation sensitive detectors (mostly semiconductor detectors), which consists of one or sometimes several rows of pixels (lines) to capture information. The counterpart to the line sensor is the area sensor, which has a rectangular arrangement (matrix) of pixels.

Line sensors are based on the original development for data storage from 1969 and have not changed significantly to this day. The light-sensitive sensors are very suitable for scanning documents in order to capture an image. The detector runs close to the original, scans the document line by line and combines the information from the individual scan lines to form an overall image. Sometimes only one line is used; sometimes a separate line is used for each color channel (red, green, blue).
This technology is still employed today in scanners, fax machines and copiers because it is very cheap and available in large quantities.

A major disadvantage of using this type of sensor in scanners is that the image capturing takes a comparatively long time due to the sequential scanning and that mechanical wear always takes place due to the movement of the components. This can lead to premature wear, especially with production scanners that have to digitize large quantities of documents in continuous operation.

In addition, the depth of field of line sensors is very small and covers only a few millimeters. Particularly in the case of books with a deep book fold or wavy pages that are not completely flat, this leads to blurring or even loss of information in the digitized material.

At book2net, we therefore only use image area sensors in our scanning systems.


Every camera needs a lens to project the object or the image to be captured onto the sensor. Lenses come in a variety of designs for a wide range of applications: Macro, back-magnification, telephoto, wide-angle, zoom or tilt-shift lens. Basically, lenses can be adjusted in two ways: focal length and aperture. The focal length determines how close or how far away objects must be to be in focus. This is also referred to as focusing. The aperture controls how much light falls through the optics onto the sensor. If the aperture is wide open, a lot of light falls on the sensor and the depth of field is basically shallow. If you close the aperture, the image becomes darker, but the depth of field increases.

In our systems we use a special lens, which was designed for the digitization of documents and books. Here we pay a lot of attention to a distortion-free image in order to avoid deformations of the documents. This ensures that the documents are also scanned and displayed at right angles and true to scale. In addition, the lens we use differs from other commercially available lenses in that it is apochromatic corrected and has extremely high sharpness even in the peripheral areas. This is because unlike in photography, when digitizing, the important image information is not only in the center of the image, but also, or especially, in the peripheral areas.


LEDs (light-emitting diodes) are energy-saving light sources (ESL). In contrast to conventional light bulbs, LEDs achieve 30-50 times the lighting duration, which corresponds to about 50,000 hours. Consequently, an LED can burn for up to 2083 days or more than 5.5 years. Despite their higher initial cost, they are therefore much more economical than conventional lighting.

Our boo2net devices meet the highest conservation and ecological requirements. The Fresnel lenses specially developed for the book2net lighting units are a significant technological advantage over lighting from other manufacturers. They ensure perfect light distribution and illumination. Unwanted and disruptive gradients and reflection effects, which otherwise occur in very in very bright or very dark areas and also with glossy materials, are avoided.