LED Measurement System

As we know, there are many light sources which can be used for lighting system. In the past, when the electricity hasn’t been used for lighting technology, candle and torch were used for it. Thomas Alfa Edison started lighting technology by his invention, incandescent lamp. Then, fluorescent lamp technology has been being used. Now, the development of LED light has begun to replace fluorescent lamp and other light source. LED is light source whose its efficiency is very high because it converts directly from electricity to light.

As a light source, LED has properties as other light source, such as: Flux Luminous, Intensity, Luminance, Radiance Flux, etc. Measuring these properties needs instrument or equipment. The development instrument technology makes the measurement of Light properties (especially LED light properties) become easier. To measure LED light properties need at least spectrometer, integrating sphere, fiber optic, and software. Several companies has developed this kind of instrument in one system.

Spectrometer

Spectrometer is equipments that analyzed the wavelength of light. Light that comes to spectrometer will be refracted by prism or grating, so light will be separated based on its wavelength. This wavelength will be analyzed by CCD to be converted into electric signal.

Fiber optic

Fiber optic is used to be path of light. Fiber optic is put in front of light source, so light can enter to the fiber optic and go to spectrometer to be analyzed

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Integrating Sphere

Integrating sphere is a hollow sphere which is coated by white color. The function of integrating sphere is to collect 

all of light emitted by light source.

PC and software

Electric signals from spectrometer are the information of light. To know what signal said, it needs process to be understood. This process is done by computer with compatible software. Spectrometer is usually completed by its software.

Photometry Quantities

Photometry is defined as a science that study about light which is perceived by human eyes. It is different with radiometry which measure all of radiant energy including visible light. Photometry focus radiant energy which is sensitive to human eyes, that is wavelength range from 380 nm to 750 nm.

IEC said light is energy radiation which can be evaluated visually. Gigahertz-Optic defined light as part of electromagnetic spectrum radiation which can be seen. The point of these definitions is same but in different words. There are several parameters in Photometry: Luminous flux, Luminous Intensity, illuminance and Luminance.

Luminous flux is the total power electromagnetic radiation emitted by source which the spectral is can be sensed by human eye. In other words, it is on in range of visible light (380 nm -750 nm). Unit of this parameter is Lumen. 

Luminous Intensity is total luminous flux per unit solid angle that emitted in certain angle. Unit of this parameter is Lumen/steradian or Candela (cd).

Illumninance is the total luminous flux which is received by a certain surface area. Unit of this parameter is Lumen/m² or Lux.

Luminance is total luminous intensity which is received by a certain surface area. Unit of this parameter is candela/m².

These parameters are similar with radiometry. The difference is photometry measure only electromagnetic radiation than can be sensed by human eye.

Source of light emits both of visible light and non visible light. The ratio of power in visible light range to the total radiant power is luminous efficacy which has unit Lumen/Watt.

Luminous efficiency is also known to determine the amount of visible light power in unit watt which emitted by total radiant power (also) in unit watt. This can be represented in percent (%)