Return Basic concept of LED optics

Optics is a branch of physics that studies the characteristics and behavior of light, including the interaction of light with objects, the construction, use, or detection of optical instruments.

A lamp is a device used to change the light distribution of a light source to cause light to diffuse or cause dispersion. This is achieved by the use of optical elements (reflectors, diffusers, lenses, etc.) and auxiliary components (sockets, Lead, starter, ballast, etc.). The fixture also contains parts for securing and protecting the light source and line attachments.

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▲Figure 2.1.1 Simplified combination of LED lighting functions

About optical components

The main function of the optical element is to change the light flux intensity distribution and / or to diffuse the light, causing dispersion. The optical elements of different geometries can produce different light intensity distribution curves (LIDC).

The purpose of using optical components:

Change the distribution of light flux, rule it or break it;

Reduce the brightness that the observer can feel at a certain angle - limit glare;

Change the light source through the optical components after the spectral components - filter.

On the intensity distribution curve - LIDC

Approximate point light source in the direction of the light intensity measurement, with the vector in the light source as the center of the space to be marked, and then the end of each vector connection, you can get the plane of the brightness of the surface (Note: This is a 3D surface ).

In the calculation, usually only need to know the 3D surface of several specific sections of the numerical distribution is enough, these sections are usually through the center of the light source. In this way, we get the light intensity distribution curve under polar coordinates.

LIDC is usually displayed on a plane passing through the center of the light source or lamp. The most commonly used beam surface is C-γ (Note: that we often say C plane), its axis is perpendicular to the main light side of the lamp.

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▲Figure 2.1.2 Standard (EN13032-1) Light intensity distribution curve section system

When the intensity distribution curve is made, the light intensity is expressed by the light flux of 1000 lm, which is to make the light intensity distribution curve of the light source not affected by the luminous flux of the light source.

The lighting space requires a different light distribution curve to meet the criteria for a particular application or visual operation (see Figures 2.1.3 and 2.1.4). The following are some of the different optical components of the lamps, they apply to a variety of different needs.

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▲Figure 2.1.3 Basic shape of the light intensity distribution curve

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▲Figure 2.1.4 Basic direction of light intensity distribution curve

The formula is as follows:

The efficiency of optical components - LOR (Luminaire Output Ratio)

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The efficiency of the optical element is equal to the luminous flux of the lamp and the total luminous flux of all the light sources in the lamp.

About the reflector

A reflector is an optical element that controls the light of a light source by reflection of a reflective material. The reflective material is divided into specular reflection, diffuse reflection and mixed reflective material.

The reflector is divided into two types: the first refers to four kinds of basic geometric conical reflector - oval, ribbon, hyperbolic and parabolic (Figure 2.2.1); the second refers to non-cone reflector, Such as square or asymmetric, their reflective surfaces are also basic geometries.

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▲Figure 2.2.1 Four basic geometries of the reflector

Oval Reflector - If the light source is placed at the focal point of the elliptical reflector, the beam will be reflected to another focus of the hypothetical ellipse. Such reflectors are often used in medium and wide light and light distribution lamps.

Ribbon reflector - The center of the reflector arc is outside the reflector arc and is connected by a line of different radians. The advantage of this reflector is that it can accurately project light to the desired location, but the precision of production is sensitive to the geometrical structure of the reflector.

Hyperbolic reflector - produces medium width and light distribution.

Parabolic reflector - produces narrow light distribution. Such reflectors are used in relatively small areas where high lighting levels are required.

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▲Figure 2.2.2 LED light source of the various reflectors

The Polycrystalline Reflector-Reflector contains a large number of small surfaces with different rotational angles for the reflector focus design, which ensures a better luminous flux distribution in the desired direction.

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▲ 2.2.3 Polycrystalline Reflector: Provides a better luminous flux distribution in the desired direction

On the reflector shading angle

The shading angle indicates the angle at which the light source is covered by the lamp reflector. The shading angle is the angle between the horizontal plane and the edge of the reflector and the end of the light source (Figure 2.2.4).

The shading angle is defined as follows:

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Annotation:

H: the distance from the light source of the given light source to the level of the reflector exit port

R: Radius of the exit of the reflector

R: Light source radius

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▲Figure 2.2.4 Shading angle

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▲Figure 2.2.5 Endpoints of various light sources

Figure 2.2.5 shows the light emitting surfaces of different light sources. For example, the luminous surface of a transparent incandescent bulb is the end of the filament on the other side of the filament.

About diffuser

The diffuser produces a scattering when it passes through it. Diffuse light can also be obtained by diffuse reflection of light on a white surface. Based on the diffuse principle, the diffuser is divided into the following: milky, gaussian and prismatic diffusers. (As shown in Figure 2.3.1)

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▲Figure 2.3.1 Basic type of diffusion mechanism

A diffuser with a uniform dispersion penetrating property (opal) can diffuse the light from the light source uniformly in each direction without exhibiting the shape of the light source. The diffuser (Gaussian or Prism) diffuser changes the luminous flux distribution to a specific direction, not only does not show the shape of the light source, but also reshapes the light intensity distribution curve.

Milky white diffuser - milky white diffuser - the light through the distribution of uniform distribution of particles containing ordinary diffuse material, resulting in cosine light intensity distribution curve.

Gaussian diffuser - produces a Gaussian light intensity distribution curve. The light passes through the fine structure surface like a sandblasting surface and is scattered in a different direction.

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▲Figure 2.3.2 Comparison of milky white diffuser and Gaussian diffuser


Prism-type diffuser - combined by micro-prism diffuser, which is fundamentally a refraction lens. According to the law of refraction, geometries such as pyramids, hexagons, ball arches and triangular pyramids can be used to create the desired light intensity distribution curve.

They are usually used in lamps that require high lighting quality indicators (UGR-glare value; average brightness of Lavg lamps).

The following is an example of the most commonly used microprism diffuser:

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▲ straight line 115 ° prism

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▲straight 90 ° prism

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▲Grid 90 ° prism

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▲Square cone prism

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▲Triangle cone prism

About the lens

A lens is an optics with precise or near-axial symmetry characteristics that allow light to penetrate and refract, thereby converging or diverging the beam.

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▲Figure 2.4.1 Two basic types of lens-convex (convergent) lenses

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▲Figure 2.4.1 Two basic types of lens-concave (divergent) lenses

A single lens contains an optical element. A composite lens contains a series of coaxial single lenses. Using a multi-lens combination can reduce more aberrations than using a single lens. The lens is made of glass or transparent plastic.

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▲Figure 2.4.2 Different types of lenses used by LED light sources