Explain the goniophotometer and how does it differ from integrating sphere?

A LM-79 goniophotometer is an instrument for measuring the light reflected off an object at various viewing angles. It is somewhat considered like integrating sphere spectrophotometer.
Most recently used LED-light sources are usually directed light sources with a non-uniform spatial distribution of light, necessitating the employment of goniophotometers.
A Lambertian source is one whose light is distributed uniformly. The spatial dispersion of light is of considerable relevance in vehicle lighting and design due to rigorous requirements.

What is goniophotometer
A light emits light when it is turned on. This light varies in hue, “strength,” and intensity according to the angle at which it is seen. The wavelength, phase, frequency, amplitude, etc., are some categories into which these attributes fall.
The LM-79 goniophotometer can measure a light source’s luminous flux and the luminous intensity distribution. Color temperature and color consistency may be measured by several tools as well. With the proliferation of LED lighting technology, the goniophotometer has widespread use.
Lambertian sources, such as those created by LEDs, are biased toward focusing light in a certain direction. An ordinary bulb emits light in a nearly uniform radial distribution, with about the same amount of brightness in each direction. The goniophotometer is widely used in the automobile sector to analyze the color temperature of headlights and ensure they are legal.

Luminous flux
The entire quantity of light from a given source is called its luminous flux. No matter which way you turn. A laser, for instance, emits a tremendous quantity of light in a pinpoint area but almost none in any other direction. In contrast, a traditional incandescent light bulb emits the same amount of light in every direction. Both light sources may have the same overall output. In contrast to the previous lightbulb, which dispersed the light across a wider region, the laser concentrates it all into a single point.

Luminous intensity
The luminous intensity of a light source is the total quantity of light seen at a given distance and viewing angle. It is possible for the luminous intensity of focused light to be very high when seen at one angle and nearly nonexistent when viewed from another. In this scenario, the laser above would emit light most brightly in a single pinpoint location but very dimly or not in any other direction. The old bulb’s illumination would be uniformly dim but in all directions.

Distribution of color temperature
Certain kinds of light are used to determine the color temperature distribution. These temperatures go from about 1000 kelvin (slightly red) to 27000 kelvin (very blue-ish). Generally speaking, “warm white” refers to a color temperature between 2500 and 5000 kelvin, whereas “cold white” refers to a color temperature between 5000 and 7500 kelvin.

Color uniformity
Light’s characteristics may shift when seen from various vantage points and distances. When the color temperature is consistent across all viewing angles, the color uniformity is high; when it varies widely from one viewing angle to the next, the color uniformity is poor.

Goniophotometer Design
The goniometer is the other half of the equation; it spins and tilts the light source under examination relative to a stationary photometer. Measuring the luminous intensity throughout the range of angles the light source radiates into is necessary for a comprehensive description of a lamp’s or luminaire’s output. This implies that it must measure the light output of a downlighter-style luminaire across a solid angle of 2 pi steradians. In contrast, it must measure that of other light sources (such as incandescent lights) over a whole sphere (4pi steradians).

Motion of goniophotometer
Light is measured when the equipment under test is rotated and tilted by a goniometer in most commercial goniophotometers, with the light meter remaining stationary. The “moving mirror” goniophotometer is a variant in which the lamp is again moved on its azimuthal axis. A mirror around the lamp redirects the light to a stationary photodetector. The light source is rotated along its azimuthal axis in a different kind of goniophotometer. In contrast, a set of photodetectors placed in an arc around the source collects the incoming radiation.
Solid-state lighting (SSL) that relies on LEDs is often unaffected by the direction in which it is used. On the other hand, this presupposes that the product has good heat sinking. In certain circumstances, such as with metal halide discharge lamps, the light output will vary somewhat depending on the direction of the light source about gravity.
LISUN provides the best goniophotometers for testing.

Type A and B motion
Type A and B goniophotometers are functionally equivalent; in both instances, the device to be tested is rotated by ninety degrees around its horizontal and vertical axes. The relevant horizontal-vertical coordinate system for type A or B (H-V or X-Y). Type C motion goniophotometers move the device being tested in two planes, one of which is called the azimuthal axis and the other the elevation (or inclination) axis.

Type A or B motion
During a scan with a LM-79 goniophotometer of either type A or type B, the device under test will be tilted relative to gravity, changing its orientation (burning position). Type C goniophotometers need the instrument to be held at a fixed angle about the center of the Earth. International lighting standards like IES LM-79-18, EN 13032-4, and CIE S025 mandate the use of a type C goniophotometer to measure the sample to eliminate inaccuracies caused by a lamp or luminaire being tilted concerning gravity. Further, a correction factor should be calculated and added to the data if the sample is placed on the goniophotometer at an angle other than the intended orientation.

Type A/B motion
Type A/B motion goniophotometers are the gold standard when evaluating directed lighting products. Vehicle lighting and other transportation/avionics lighting/signaling equipment testing is a common use case. Lamps, luminaires, and other architectural lighting products are often measured with goniophotometers of type C. Some SSL Resource type C goniophotometers are convertible to type B motion (and vice versa) by purchasing an optional accessory kit. Due to its adaptability, a single goniophotometer can measure the output of directed vehicle illumination and architectural luminaires.

How does goniophotometer differ from integrating sphere
A goniophotometer and an integrating sphere are used to measure light intensity in a process known as photometry. Both have distinct advantages that make them well-suited for certain flux testing and measuring applications.
Despite their shared use, both methods of measuring optical power have distinct hallmarks and operating principles. Different instruments examine various types of lights (or other illumination sources), so it’s important to keep that in mind and the apparent differences in how these gadgets work. This is where the two are most different from one another. The eight main distinctions between an integrating sphere and a LM-79 goniophotometer are discussed below.

Differences Between a Goniophotometer and an Integrating Sphere
What is a goniophotometer?
A goniophotometer is a photometer used to determine how strong a light source appears from various viewing angles. It is often used to measure the output of directional lights like LEDs and car headlights.
It works similarly to a photometer except that instead of a fixed mirror, it uses a rotating arm to reflect light. This mirror receives a constant stream of light from a variety of directions (as the arm rotates), allowing for the measurement of the source’s luminous flux, intensity distribution, and efficiency.

What is integrating sphere?
The power of unfocused light sources may be measured using an integrating sphere, a spherical-shaped device. Light enters the sphere via microscopic holes, reflects off the internal coating, and is dispersed uniformly within using the principle of diffusion. The measurement of flux and many other operations are made possible by this.
The term “Coblentz square” may be used interchangeably with “integrating sphere” or “Ulbricht sphere.” The inner structure of the latter is reflective, in contrast to the diffuse one of the former, which is used in the integrating sphere. The most critical part of the calibration procedure is the sphere’s inside covering.

Measurement of Total Power
An integrating sphere’s primary benefit over a goniophotometer is that it can determine an object’s total luminous intensity with a single reading. You won’t have to do any iterations if you utilize the former.
Because of this, the integrating sphere is a highly sought-after photometry tool. LISUN’s models of integrating spheres are state-of-the-art and well suited to use in industry.

Accuracy Dependence
As previously established, an integrating sphere’s accuracy depends only on the inner coating applied. Both the number of iterations and the number of points matter in goniophotometry. The average results from all the repetitions might be used as a rough estimate.

Applications
These two tools are used interchangeably to measure the intensity of a given beam of light. However, there is a distinction between them in terms of the dispersion of light and the information about geographical distribution.
The LM-79 goniophotometer is most useful for measuring point sources of light. Measurements taken with a meter like this will be more precise for lights that don’t radiate in all directions. For more accurate readings of the ambient light power, an integrating sphere is the tool of choice.
Suppose you want to measure the total luminosity in your living room (which likely has more than one light source, such as a ceiling light, a table lamp, and possibly even some Christmas lights). In that case, you can do so with the help of an integrating sphere, which will collect light from all of these points in one place. It can’t do this with a goniophotometer.
Therefore, integrating spheres are the tool of choice for evaluating the efficacy of light sources in radiometric and industrial settings.

Cost Differences
Historically speaking, the cost of integrating spheres was high. A goniophotometer, which uses expensive spatial mirrors, offers an alternative but is significantly more costly. In addition, such a meter’s constituent elements are rather expensive.
Note that while selecting instruments, functionality is more essential than cost.

Color Uniformity Testing
When comparing integrating spheres with goniophotometers, the latter’s capacity to reliably test for color uniformity and temperature is clear. Color sensors allow for the measurement of these supplementary features.
Light distribution and spatial variables cannot be determined using an integrating sphere.

Different Types
In terms of types, an integrating sphere is equivalent to the previous example. It comes in a few sizes and may be run manually or automatically, but that’s it.
Three main varieties of goniophotometers are designated A, B, and C. This necessitates adjustments to the axis’ rotational freedom. In contrast, to type A, which has a stationary horizontal axis, types B and C are vertically oriented. There are a variety of lamp kinds that utilize these.
Spotlights and fluorescent tubes both employ the type C bulb.

Speed of Operation
Although this is a contentious subject, the general opinion held within the industry is that an integrating sphere can complete the measurement in a shorter amount of time than a goniophotometer. This is because the latter requires a significant amount of time to rotate its arm for a single cycle.
Even though it takes an extra detector to complete the measurement, using an integrating sphere is a rapid way to collect the data you need.

Maintenance Aspect
If the source of light in an integrating sphere is very powerful, it might harm the coating on the sphere. It cannot avoid this circumstance, and if the sphere is to be used again, the coating will need to be replaced. This might turn out to be a very pricey endeavor. Barium sulfate and magnesium oxide are two of the materials that are put to use to accomplish this.
A goniophotometer is a gadget that requires frequent upkeep since it has a large number of moving elements. The cost of repairing or replacing these components might be rather high, even though they are readily accessible on the market. The need to know how the process works and make intelligent decisions arises.

Conclusion
The main distinctions between an integrating sphere and a LM-79 goniophotometer are stated above. For a seasoned professional in photometry, it’s a practical question of which method to choose. These considerations, however, will aid in grasping the essential distinctions.
Both systems date back to the early twentieth century and have evolved significantly since their inception. In this case, it’s up to the engineers to ensure they’re getting their supplies from reliable sources.

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