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The Optical Properties Of LED Light Sources

Human wisdom has made filament lighting more convenient in modern times. Incandescent lamps, fluorescent lamps, metal halide lamps, and high-pressure gas discharge lamps are representatives of this era; and in this century, solid-state lighting (SSL-SolidState Lighting) that exceeds filament lighting has come out. LED lighting has accelerated into various fields of lighting; despite the rapid development of lighting technology, sunlight is still the best light source among all light sources. Now, with the advent of near-solar spectrum LED products, human beings have taken another big step towards finding the best lighting source.

Let’s take a brief look at the optical characteristics of LED light sources.

#1 Spectral Distribution

Spectral distribution shows the characteristic of optical power as a function of wavelength for a given light source.

All colorimetric information. Based on the spectrogram, chromaticity parameters such as color coordinates, color temperature, and color rendering index can be calculated.

A certain spectrum corresponds to a certain color;

But a certain color cannot correspond to a certain spectrum.

#2 Color Temperature

When a black body is heated to a temperature, and the color of the light emitted by it is the same as that of the light emitted by a light source, the temperature at which the black body is heated is called the color temperature of the light source, that is, the color temperature.

  • High color temperature light source with high relative power in the long-wave band spectrum;
  • Low color temperature light sources have relatively high power in the short-wave band spectrum.

#3 Color Rendering Index

The color rendering index indicates the ability of the light source to reproduce the color of the illuminated object.

  • Compare the color difference of the standard color blocks under the illumination of the measured light source and the standard light source;
  • The emission spectrum of the light source is continuous, and the relative intensity is close to the standard light source, the higher the color rendering index is;
  • The emission spectrum of the light source is discontinuous, but the light color of the missing spectrum can be synthesized by other existing spectra, and the light source can also detect a higher color rendering index.

#4 Chip Size, Quantity, Arrangement

The size, quantity, and arrangement of chips are one of the important factors affecting the light distribution design and optical quality.

  • Chip layout density
  • Chip arrangement uniformity
  • Distance between chip and perimeter

#5 Coating Of Phosphor Powder

  • Phosphor Thickness
  • Boundary Phosphor Area

#6 Package Structure And Light Distribution Curve

Planar packaging: the light extraction efficiency is relatively low, the interface reflection is relatively serious, the light distribution curve is continuously smooth, and the light emitting angle is generally slightly greater than 120°.

Spherical package: The center of the light-emitting surface of the chip is generally located at the center of the hemisphere of the package. It is mostly used in a single chip package. The light output efficiency is high, the light distribution curve is continuously smooth, and the light-emitting angle is generally 110°.

Shaped packaging: it refers to the phenomenon that the light surface appears discontinuous and the surface shape changes more seriously during the packaging process. This kind of packaging often has a relatively small light output angle, and generally adopts a direct light output method, which is not good for secondary light distribution.

In practical applications, it is necessary to select different light sources according to the optical characteristics of LED light sources and apply them to different scenarios.

LED Light Guide