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.

Fiber optic

Fiber optic is often used in telecommunication network. Comparing with electrical cable, signal transmission by fiber optic is faster because it uses light as a signal. Besides that, it is also immune to electromagnetic interference, transmits longer distance, and higher bandwidth data rates. How can fiber optic be a path for light?

Light can travel from edge of fiber optic to another edge. The principle of fiber optic is total internal reflection. Before discuss about total internal reflection, let us review about light refraction. Light will be refracted when light through different medium which their refraction index value is different. For example, if light is emitted from inside the water with certain angle, then it will be refracted when comes out from water to the air. The phenomenon of light refraction is the angles are different. If refraction index of medium where the light comes from higher than refraction index of medium where light goes on, the angle will be bigger. If the initial angle is enlarged, there will be a critical angle, that is the angle when the light is not transmitted to the second medium. Moreover, if the angle is still enlarged, the light will be reflected as total internal reflection.

Fiber optic consists of core and cladding. Core has higher refraction index than cladding, then if light travel inside core with the angle more than critical angle, so there will be total internal reflection. By this phenomenon light can travel from one edge to another edge.