Use of the Ulbricht sphere in measuring luminous flux

An integrating sphere is one of the most important instruments in the measuring of light. An Ulbricht sphere is a device that catches all of the radiation emitted by a light source all at once. The essential features of a lamp when it comes to light measurement are those that manufacturers and end-users consider the most significant. The amount of lumens, the color, and the efficiency are the three factors to consider (how many lumens of output per watt of energy).

It is possible to calculate lumens by multiplying the spectral radiant flux by the eye’s photopic response. The two most fundamental kinds of equipment used to measure luminous flux are photometers and spectroradiometers, and we will take a brief look at both of them in this article.

An optical device that measures light directly and by the photometric system is a photometer or a photometer instrument. To operate a photometer properly, a filtered detector must be used, with the relative spectral response of the human eye as close as possible. Various names for the spectrum response associated with this phenomenon have been proposed, including the CIE luminous efficiency function, the V-lambda function, and, more frequently yet, the photopic response curve. LISUN provides the best Ulbricht sphere worldwide.

When properly determining the luminous flux of a light source, an integrating sphere is your best choice. When working with an integrating sphere, you have access to all spectrum data at your disposal. With little effort, you may transform the spectral data into significant color characteristics such as chromaticity, associated color temperature, and color rendering indices.

When using a photometer with a filtered detector, on the other hand, it is not feasible to simulate the CIE luminous efficiency function perfectly, which results in measurement inaccuracy. Check out this video series to learn more about light measurement using an integrating sphere spectroradiometer, in which we show the process using our LISUN light measurement equipment.

Methods to measure luminous flux
Although using an Ulbricht sphere to measure luminous flux or radiant power is more time-consuming than using integrating spheres, the results are much more accurate than with integrating spheres. In contrast to sphere photometry, this measurement method does not need the use of luminous flux standard lamps as a reference value, as is the case with the latter.

It is the technique of choice for measuring lamps with varying luminous intensity distributions. It serves as the baseline for calibrating luminous flux standard lamps, which serve as the reference value for other test methods once they have been calibrated. Another characteristic that distinguishes goniophotometry from sphere photometry is the ability to quantify partial luminous flux and angle of half intensity, which are impossible with sphere photometry.

Large distances are required for the light intensity distribution to satisfy the far-field criterion to be effective. To estimate total flow using a goniometer, it is not necessary to measure across a vast distance. As long as the detector has a good cosine response, it can measure irradiance reliably from all directions. Irradiance is not a characteristic of the lamp but refers to the amount of light that falls on a surface.

By measuring the irradiance at a sufficient number of points around a virtual sphere surrounding the lamp, it is possible to calculate the total flux by integrating the data. If there are no interactions between the source and the detector, the size of the source may be nearly as large as the size of the virtual sphere.

Lisun Instruments Limited was found by LISUN GROUP in 2003. LISUN quality system has been strictly certified by ISO9001:2015. As a CIE Membership, LISUN products are designed based on CIE, IEC and other international or national standards. All products passed CE certificate and authenticated by the third party lab.

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