Uniform light source with integrating sphere – luminance and radiance standard
Opsytec luminance and radiance standards are homogeneous light sources based on an integrating sphere that emit uniformly and almost perfectly Lambertian across their entire emitting surface. They are used in photometry and radiometry, in particular for the calibration and characterization of cameras and optical measuring devices, and for determining reflection, transmission and absorption properties of materials. Diameters from 75 mm to 2500 mm are available with coatings of barium sulphate, PTFE or gold.
The underlying quantities are explained in Radiometric quantities.
The mode of operation is based on the principle of the integrating sphere. The integrating sphere consists of a hollow, spherical structure with a highly reflective inner surface. This surface is coated with a diffuse reflective coating of barium sulphate, PTFE or gold, which, depending on the material and wavelength, scatters up to 99% of the incident light. This property enables the sphere to distribute the light evenly in all directions and eliminate directional effects.
For luminance standards and radiance standards, the light sources are positioned outside and shine into the sphere.
Each Opsytec integrating sphere is manufactured to the customer‘s individual requirements to ensure optimum performance for specific applications.
Another feature of the luminance and radiance standards from Opsytec Dr. Gröbel GmbH is their ability to integrate multiple light sources simultaneously. These can optionally be operated individually or in groups and can be dimmed or fitted with a manual or motorized mechanical diaphragm. Shades are used if the luminance and radiance levels need to be adjusted but the lamps cannot be dimmed or change spectrally.
Reference examples: luminance and uniformity
Two standards that have been built show the luminance and uniformity an integrating sphere achieves as a uniform light source:
| Set-up | Light sources | Luminance | Uniformity |
|---|---|---|---|
| Sphere 300 mm, exit port 50 mm, barium sulphate | 4 halogen lamps (max. 8) | 12,000 cd/m² | above 99.5% over the entire area |
| Sphere 2500 mm, exit port 1200 mm, PTFE | 25 halogen lamps of 1000 W each, one of them with a motorised iris diaphragm | 76,000 cd/m² | above 98% over the usable area |
The exit port occupies around 0.7% of the inner sphere surface for the 300 mm sphere and around 6% for the 2500 mm sphere. The larger the exit area in relation to the sphere, the harder it is to maintain uniformity.
Calculate radiance and luminance individually
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The luminance and radiance an integrating sphere achieves depends on the diameter, coating, port size and lamp configuration. The calculator shows the radiance, luminance and spectral radiance at the exit port – with barium sulphate, PTFE or gold – and provides an initial design including a 3D view and PDF report before we go into the details together.
The following lamps are possible as homogeneous light sources for luminance or radiance standards:
Halogen lamps are commonly used because they offer a continuous spectrum in the visible range. They are ideal for applications that require high color fidelity and a continuous spectrum. Halogen lamps are also available in different wattages, allowing flexibility of choice.
Light emitting diodes (LEDs) are increasingly being used for luminance standards and radiance standards. LEDs offer several advantages, including long life, energy efficiency and the ability to select specific wavelengths. LEDs enable precise control of light intensity and a fast response time, which makes them particularly attractive for modern applications. The luminance achieved is higher than that of conventional integrating spheres with halogen lamps.
Deuterium lamps produce a continuous spectrum from about 200 to 400 nm, making them ideal for applications requiring UV radiation.
IR emitters, such as tungsten emitters, produce a continuous spectrum with a maximum in the near to mid infrared range and are often used in IR spectroscopy and thermography. IR emitters are also available for vacuum applications.
These lamps are used as luminance and radiance standards in the following homogeneous light source applications:
- Calibration of measuring devices for luminance and radiance
- Generation of a homogeneous light source with defined luminance values for the characterization of camera systems
- Provision of reference values for quality control in the lighting industry
- Supporting research and development in the field of optics and photometry
- Characterization of reflection, transmission and absorption, where uniform illumination ensures the results.
Technical data, accessories & holders for luminance / radiance standards
| Diameter | 75 mm - 2500 mm |
| customer-specific on request | |
| Coating | Barium sulfat (BaSO4) |
| PTFE | |
| Gold | |
| Wavelengths | BaSO4 300–2400 nm |
| PTFE 200–2500 nm | |
| Gold 0,7–20 µm | |
| Ports | 1 (Standard) |
| Lamp ports | 1–25 |
| Accessories | UControl control unit |
| RMD sensors | |
| Spectrometer | |
| Port apertures |
Order numbers, scope of delivery, accessories and versions
| Coating | Wavelength range |
|---|---|
| Barium sulfate (BaSO₄) | 300–2400 nm |
| PTFE | 200–2500 nm |
| Gold | 0.7–20 µm |
The coating determines the usable wavelength range. If you are not sure which is the right one, we are glad to advise you.
| Inner diameter | Note |
|---|---|
| 75 mm | |
| 100 mm | |
| 150 mm | |
| 300 mm | |
| 500 mm | |
| 600 mm | |
| 800 mm | |
| 1000 mm | |
| customer-specific | please state it with your enquiry |
The order numbers of the spheres are given on the page integrating spheres; a standard is the sphere, the lamp and the control together and is assembled for your measuring task.
| Number | Note |
|---|---|
| 1 to 25 | depending on the required radiance |
Available as accessories: the UControl control unit, RMD sensors, spectrometers and port baffles.
The example shows a radiance standard with an output port of 1200 mm and a diameter of 2500 mm. 25 halogen lamps (1000 W each) were used, one of them with a motorised iris diaphragm. The luminance of the large integrating sphere is 76,000 cd/m². The homogeneity is over 98% on the surface to be realised. material: PTFE
Frequently asked questions about uniform light sources
Very uniform, provided the exit port is small compared with the sphere. An Opsytec luminance standard with a diameter of 300 mm and an exit port of 50 mm achieves a uniformity of above 99.5% over the entire area, a radiance standard with a diameter of 2500 mm and an exit port of 1200 mm above 98% over the usable area. The larger the exit port in relation to the sphere, the harder it is to maintain this uniformity.
A luminance standard specifies the luminance in cd/m², i.e. the radiation weighted with the spectral luminous efficiency V(λ) of the eye; it is used to calibrate cameras and luminance meters in the visible range. A radiance standard specifies the radiance in W/(m²·sr) or, spectrally, in W/(m²·sr·nm) and is not tied to V(λ) – with a deuterium lamp or IR emitter also for UV and IR applications. Both are based on the same integrating sphere; the light source and coating determine the spectral range.
The sphere diameter follows the exit opening, because uniformity depends on the ratio of port area to inner sphere surface. With a 50 mm exit port in a 300 mm sphere this is around 0.7% and the uniformity is above 99.5%; with a 1200 mm exit port in a 2500 mm sphere it is around 6% at above 98%. Opsytec manufactures luminance and radiance standards from 75 mm to 2.5 m; the integrating sphere calculator on this page calculates the luminance and radiance a design achieves.
Publications using Opsytec integrating spheres
We do not keep a separate bibliography for this individual device – publications usually name the product family, not the model. Listed here are the 3 most recent works in which Opsytec integrating spheres were used.
| Title | Authors | Journal | Year |
|---|---|---|---|
| Luminescence and Photochromism in Lanthanide‐Doped Hackmanites | Baggott, J.; Tuomisto, M.; Williams, J. A. G. et al. | Advanced Optical Materials | 2026 |
| Customizing Tactile and Visual Perceptions of Organic Light–Emitting Diodes by Surface Coatings | Buhl, J.; Cojocaru, A.; Gerken, M. | Advanced Intelligent Systems | 2021 |
| Design of Instrumentation & Control and Optical Table Instruments for the Divertor Flow Monitor Diagnostic at ITER | — | — | — |
