June 30, 2022

The increase in use of LED’s around the world is pretty prominent. However to produce durable and effective LED’s, they have to be tested thoroughly in the formulation phase. This testing is done through a number of different instruments, one of which is an Integrating Sphere. This article will explore what exactly an integrating sphere is, its theory as well as its applications. 

Contents

Integrating Sphere 1

Working of an Integrating Sphere 1

Theory of Integrating Sphere 2

Applications of Integrating Sphere 2

Conclusion 3

Integrating Sphere

The integrating sphere measures the overall flux output of the source. It captures all of the rays emitted by the object and reflected by the sphere’s reflecting covering on the inside. The total luminous flux of a light source is measured by an integrating sphere, which must be distinguished from illuminance. This instrument is used in conjunction with a spectroradiometer, such as those produced by LISUN, to measure the light from single LEDs and LED lighting devices.

Working of an Integrating Sphere

Such a sphere has an entry port as well as one for departure. The light source is adjusted near the entrance port while the detector is adjusted at exit port. Here, the former captures all emitted light while the latter is where all reflected beams converge, allowing the total flux from the light source to be measured. 

Overall, an integrating sphere can be utilized to make optical, photometric, and radiometric measurements. The integrating sphere’s spherical shape integrates light within the sphere, making it easier to catch light. With respect to the spectral range, a variation in the coating inside the surface is seen. IR ranges are usually coated with gold, while ultraviolet and visible ranges are coated with Teflon. 

Theory of Integrating Sphere

An integrating spheres is meant to spatially integrate radiant flux. The light that passes through the sphere is initially diffused by the reflecting surface. Then the derivation of the radiance of the inner surface of the sphere takes place, where the average reflectance and the sphere multiplier are established after which the sphere’s time constant is presented.

The theory of Integrating spheres basically comes to the conclusion that the total radiant power emitted by a source inside the sphere or entering the sphere through its entrance port determines the sphere’s inner surface irradiance. Irradiance levels are unaffected by the geometrical and directional distribution of the primary source’s radiation as long as direct lighting of the respective site is avoided. When such an instrument is employed as the input optical element of a radiant power detector, this quality becomes even more significant.

Furthermore, the directional distribution of radiation reflected by an area of the sphere’s inner surface shielded from direct illumination is continuous and irrespective of the precise position where the reflection occurs. When a sphere is employed as a standard calibration source, this feature becomes even more important.

Applications of Integrating Sphere

A very well-known use of Integrating Spheres is to measure light output of LED’s as well as calibration of light output measurements. This is seen in the case of cameras where the uniform light source is the integrating sphere. Combined with a photodetector, it can measure the total geometric reflux emerging from a light source as well as an illuminated areas flux density. The light source’s spectral properties help figure out appropriate photodetection system. 

As the fraction of flux received by a photo-detector mounted on the sphere surface being nearly equal to the product of fractional surface area consumed by its active area, it is also utilized in measurements of high power laser sources. Furthermore, the power output of industrial CO2 lasers can be measured with it as well.

Transmission and reflection properties of objects can also be measured through it. An object can be placed at the integrating sphere’s entrance port, with a light source behind it, and the transmitted light bounces off the reflecting covering and is gathered by the detector. The same measurement can be made by removing the item and measuring the light source’s output flux directly, and then calculating transmittance. Alternatively, the object can be put diagonally across from the entrance port and the object’s reflectance measured.

Conclusion

Looking at the theory and applications of an Integrated Sphere, we see that it is a sophisticated device with a number of uses, a prominent one pertaining to LED’s. If it were to be used properly in testing, it can surely bring about impactful developments regarding LED’s.

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