Basic Concepts of Lighting Engineering
In lighting engineering, as in any branch of science and technology, there are a number of concepts that characterize the properties of lamps and lighting fixtures in standardized units of measurement. The most important of them are given below in brief.
Light and radiation.
Light is understood as electromagnetic radiation that causes a visual sensation in the human eye. In this case, we are talking about radiation in the range from 360 to 830 nm, which occupies a tiny part of the entire spectrum of electromagnetic radiation known to us.
Luminous flux Ф.
Unit of measurement: lumen [lm].
Luminous flux Ф is the entire radiation power of a light source, estimated by the light sensation of the human eye.
Luminous intensity I characterizes the power of the luminous flux of a lamp Ф in a solid angle W
Luminous intensity I.
Unit of measurement: candela [cd].
A light source emits a luminous flux Ф in different directions with different intensities. The intensity of light emitted in a certain direction is called luminous intensity I.
Image of luminous intensity in polar coordinates
Illuminance E.
Unit of measurement: lux [lx].
Illuminance E reflects the ratio of the incident luminous flux to the illuminated area. Illumination is equal to 1 lx if the luminous flux of 1 lm is uniformly distributed over an area of 1 m2.
Illumination E
Brightness L.
Unit of measurement: candela per square meter [cd/m2].
The luminosity L of a light source or illuminated area is the main factor for the level of light sensation of the human eye.
Brightness L
Basic lighting formulas:
Luminous intensity I [cd]
Illuminance E [lx]
Illuminance E [lx]
Brightness L [cd/m2]
Luminous efficiency h [lm/W]
Luminous efficiency h.
Unit of measurement: lumen per watt [lm/W].
Luminous efficiency h shows how efficiently the consumed electrical power is converted into light.
Color temperature.
Unit: Kelvin [K].
The color temperature of a light source is determined by comparison with the so-called “black body” and is displayed by the “black body line”. If the temperature of the “black body” increases, the blue component in the spectrum increases, and the red component decreases. An incandescent lamp with warm white light has, for example, a color temperature of 2700 K, and a fluorescent lamp with daylight color is 6000 K
Color of Light
Different people perceive the same color differently. Figuratively speaking, the concept of a particular color is simply the result of an unwritten agreement between people to call a certain sensation of the optic nerve a specific color, for example, “red”. Moreover, in the book by C. Padgham and J. Saunders "Perception of Light and Colour" it is mentioned that "there is evidence of differences in the pigmentation of the lens in different races, which may lead to differences in colour vision." It is also known that with age the lens turns yellow, which leads to disturbances in colour identification. That is, it can be said that adequate colour perception is the result of a psychological process rather than a physical one. As you can see, science had to work hard to systematise and strictly scientifically define the characteristics of different colours of the spectrum!
If the colour of the surface of an unheated non-radiating object, that is, one of its reflective (and therefore filtering) characteristics, can be described by the wavelength or inverse