What is integrating sphere in illumination?

 A light-scattering substance, such as barium sulfate, is used to make the sphere's spherical inner surface and inner wall. The light beam (measurement light) entering the sphere is equally scattered by integrating spheres.

The measuring light shines via an aperture in the center of the integrating sphere. The sample is put at this aperture to measure the light passing through the selection and entering the sphere. If possible, the detector should be placed in a gap not directly exposed to measurement light (often at the top or bottom of the integrating sphere).

It is possible to achieve uniform radiance and brightness with the use of integrated spheres. Hollow, a spherical shell with highly reflective diffuse interior covering, is called an integrating sphere. There is no difference in the projected solid angle from any point on a sphere to any region on the sphere. This, along with the diffuse coating and many reflections, results in a uniform radiance on and radiance of the sphere's walls. This homogeneous lighting may be employed in an optical system thanks to a "port" in the sphere.

Integrating sphere in illumination

Integrating spheres is often used to evaluate scattering samples or samples that refract light, such as optical lenses. The light that passes through lenses that condense it after it has gone through a lens is used to do baseline correction when measuring transmittance in a manner that may be measured by a conventional detector (100 percent alignment).

This might cause inaccurate measurements since the sample has been irradiated, the light-sensitive detector surface protrudes from the model. It is impossible for light dispersed by a scattering sample to reach the detector's light-sensitive surface if the sample has these qualities. An example may be accurately measured using an integrating sphere because all the measurement lights are irradiated on the light-sensitive surface of the detector at both baseline correction and sample measurement after being diffused within the integrating sphere at both.

Transmittance measurement

With no sample available, baseline correction may be applied. Standard samples (e.g., whiteboard loaded with barium sulfate) are inserted in apertures on reflection sides of integrating spheres. Scattered components and linear components are both assessed in a typical transmittance measurement.

Reflectance measurement

Measurement is carried out after a baseline correction using the standard sample (e.g., whiteboard filled with Barium Sulfate), which is placed at a point where the irradiated light from a measurement aperture and its reflections pass through an integrated sphere (reflection location).

Since reflectance is measured as a function of the standard sample, it is known as "relative" reflectance measurement. It is vital to record the standard sample's reflected light to get an accurate reading. Also, keep in mind that reflectance varies when the reference sample is changed. LISUN has the top-of-the-line integrating sphere in the market.

Using a conventional detector approach, samples that cannot be accurately measured may be accurately analyzed using an integrating sphere. Integrating spheres are a good choice for measuring light-changing samples, such as semi-transparent or opaque solutions and lenses.

The functions of the optical integrating sphere tester include light receiving, uniformly illuminated object surface, spherical parallel light tube, etc. Its principle is that after light is incident from the input hole, the light is uniformly reflected and diffused inside the sphere. Below take Lisun’s optical integrating sphere system as an example to introduce it in detail.

The role of optical integrating sphere system
1. Light receiving
the light to be measured enters the integrating sphere through a small hole on the integrating sphere system, and one or two photodetectors are arranged on the inner wall, and the photo current output by the photodetector is proportional to the illuminate of the inner wall of the integrating sphere system. In this way, according to the change of the output photo current, the change of the luminous flux entering the integrating sphere can be known.
2. Evenly illuminated object surface
several bulbs (usually four or six) are evenly arranged on the inner wall of the integrating sphere symmetrically with the light exit hole. The light emitted by the bulb is diffusely reflected by the inner wall multiple times to form a uniform and bright luminous spherical surface. The integrating sphere system is used to measure the vegetating coefficient and image surface illuminate uniformity of photographic objective lenses.

The spectral reflectance of the magnesium oxide coating in the visible spectrum is more than 99%. In this way, the light entering the integrating sphere is reflected multiple times by the inner wall coating to form a uniform illuminance on the inner wall. In order to obtain higher measurement accuracy, the opening ratio of the integrating sphere should be as small as possible. The opening ratio is defined as the ratio of the area of the sphere at the opening of the integrating sphere to the area of the entire inner wall of the sphere.

The integrating sphere is also called the luminous sphere, which is a hollow and complete spherical shell. The inner wall is coated with a white diffuse reflection layer, and the points on the inner wall of the integrating sphere are evenly diffused. The illuminate generated by the light source at any point B on the spherical wall is a superposition of the illuminance generated by multiple reflections. The integrating sphere is a high-efficiency device that is mainly used to collect the scattering or emission of light from the sample inside the sphere or outside the sphere and close to a certain window. A small window on the ball allows light to enter and get closer to the detector.

The integrating sphere is a cavity sphere coated with a white diffuse reflection material on the inner wall, also known as a photo metric sphere, a luminous sphere, etc. One or several window holes are opened on the spherical wall, which are used as light inlet holes and receiving holes for placing light receiving devices. The inner wall of the integrating sphere should be a good spherical surface, and it is usually required that the deviation from the ideal spherical surface should not be greater than 0.2% of the inner diameter. The inner wall of the integrating sphere is coated with an ideal diffuse reflection material, that is, a material with a diffuse reflection coefficient close to 1.  Commonly used materials are magnesium oxide or barium sulfate. After mixing it with a colloidal adhesive, spray it on the inner wall.

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