Common Lighting Terms

◆ Like all other technology industries, the lighting industry has its own professional terminology. These specialized terms and concepts clearly define the characteristics of light sources and fixtures and standardize measurement units. Below is an explanation of important terms.

◆ Light and Radiation

◆ Visible light is the portion of the electromagnetic wave that the human eye can perceive as brightness. This part of the electromagnetic wave has a wavelength range between 360 and 380 nm, which is only a very small segment of the electromagnetic radiation spectrum.

◆ Luminous Flux Φ

◆ Unit: lumen (lm)

◆ Luminous flux (Φ) is the radiant power emitted by a light source calculated considering the spectral sensitivity of the human eye.

◆ Luminous Intensity

◆ Unit: candela (cd)

◆ Generally, the luminous flux emitted by a light source varies in intensity in different directions. The luminous flux emitted in a specific direction of visible light is called luminous intensity (I).

◆ Illuminance E

◆ Unit: lux (lx)

◆ Illuminance (E) is the ratio of luminous flux to the illuminated area. 1 lx means the illuminance on a 1 m² surface when 1 lm of luminous flux is uniformly distributed over it.

◆ Luminance L

◆ Unit: candela per square meter (cd/m²)

◆ Luminance (L) is the luminous intensity per unit projected area of a light source (or illuminated surface) in a certain direction. Luminance determines the brightness perceived by the human eye.

◆ Luminous Efficacy η

◆ Unit: lumen per watt (lm/W)

◆ Luminous efficacy (η) refers to the efficiency of converting electrical energy into visible light.

◆ Light Color

◆ The light color of a light source is its color temperature. Light color is roughly divided into three categories:

◆ Warm White: 2700~3300K

◆ Neutral White: 3700~4300K

◆ Cool White: 5700~6500K

◆ Because the spectral composition of light varies, even if the light color is the same, the color rendering of the light source may differ.

◆ Color Rendering

◆ The effect of a lighting source on the color appearance of objects (this effect arises because the observer consciously or unconsciously compares it with the color appearance under a standard light source).

◆ Fixture Efficiency

◆ Fixture efficiency (also called light output ratio) is an important standard for measuring the energy utilization efficiency of a fixture. It is the ratio of the luminous flux output by the fixture to the luminous flux output by the light source inside the fixture.

◆ Optical Formulas

◆ Luminous Intensity [cd]: luminous flux in a specific direction / solid angle Q [sr] in that direction

◆ Illuminance [lx] E: luminous flux [lm] falling on the surface of an object / area [m²] of the illuminated object surface

◆ Luminance [cd/m²] L: luminous intensity [cd] / area [m²] of the observed luminous surface

◆ Luminous Efficacy [lm/W] η: emitted luminous flux [lm] / power consumption [W]

Industrial Lighting Quick Estimation Method

◆ If time permits and computer lighting software is available to complete indoor lighting calculations and fixture layout, use it. When no computer is available and time is urgent, the following quick estimation method can be used. The quick estimation method assumes the following as calculation premises:

1. The maintained lumen value on the industrial plane is half of the new light source lumen in a new fixture.

2. The illuminated room size is typical, the room surface reflectance is conventional, and the dust condition inside the room is normal (a typical room size means the height from the working surface to the bottom of the fixture MH is less than half of the smallest room dimension).

3. Only one type of fixture is used for the given room (when the height MH from the working plane to the bottom of the fixture is greater than 6 meters, high-hanging fixtures can be used; when MH is less than 6 meters, low-hanging fixtures can be used).

◆ Calculation Process

◆ Find the recommended illuminance value A for the application site from the North American Illuminating Engineering Society (IES) industrial lighting recommendation table.

◆ Obtain the lumen value B of the light source from the supplier.

◆ Multiply the rated lumen value B by 0.5 to get the maintained lumen C of the light source.

Number of fixtures N = Room area (length × width) / Maintained lumen C × Recommended illuminance value A

Fixture spacing S = √(Room area (length × width) / Number of fixtures N)

◆ When using high-hanging fixtures, if fixture spacing S is greater than the hanging height; or when using low-hanging fixtures, if fixture spacing S is greater than 1.5 times the hanging height; then the fixture spacing S is too large. Choose a light source with one power level lower and repeat step three until the fixture spacing S meets the requirements.

Choose a suitable high-hanging or low-hanging fixture.

◆ Industrial Lighting Layout Principles

◆ Fixtures should be arranged from the center towards the boundaries. When the number of fixture rows or columns is odd, one row or column of fixtures should be located on the centerline. When the number of fixture rows or columns is even, the fixtures closest to the centerline should be at a distance equal to half the fixture spacing S from the centerline. The fixtures closest to the wall should be at a distance less than or equal to 0.5S, as shown in the figure.