SSL Resource
Photometric Testing Efficiency

Frequently Asked Questions

Q: Which one should I get, an integrating sphere or a goniophotometer?

A: With a goniophotometer you get all the same results as you get with an integrating sphere. But with a gonio you get the angular distribution information too. Besides, the limitation for the luminaire (dimensions, mass) are way broader with a goniometer.

On the other hand, goniometric measurements are more time-consuming.

Q: According to which standards are your measurements made? What about your devices?

A: The common goniophotometric measurements follow the relevant standards such as LM-79-08, CIE S 025, EN 13201-3, and EN-13032-1. These are naturally to be discussed with the customer. Just tell us, according to which standard you need your results.

Q: What file formats do your program support? Which ones should I use?

A: In photometrical measurements, both IES and EULUMDAT are supported.

IES is a major format in the USA, documented in standard LM-63 by the Illuminating Engineering Society ( LDT is a European equivalent. They contain mainly the same data, though there are some differencies, e.g. IES stores only the luminous dimensions of the luminaire whereas LDT keeps also the physical dimensions. Use the one that suites best your needs.

The other supported formats are SSL photometric system-specific GPF for goniophotometers and GCF for goniocolormeters that can be used for data saving and opening with a larger amount of information about test conditions.

Q: Can I measure automotive lights?

A: Yes. Our B/C type goniophotometer SSL GB-1200R is designed for measuring both automotive headlamps and normal luminaires. See more information about SSL GB-1200R.

Q: What are the sufficient angle steps and maximum angles?

A: These depend on the standards you are following, as well as the shape and the beam width of luminous distribution. The flux value is accurate (in this sense), if the measurement covers all the directions where there is significant light. Thumb rule for the rough estimate of angle steps is to use the value of beam width divided by 10.

In the GPM measurement program you can determine the angle steps and the maximum angles by yourselves or let the program do it automatically (GPM Pro version). 

Q: How does the optics (lenses/reflectors) affect on the measured flux?

A: All the optical components causes light losses and lower flux levels, because of back-reflections in the surface boundaries and possible opacity of the optics material. The magnitude of the total effect depends on the specular/diffuse reflectance/transmittance of inner surfaces of the luminaire. 

The other issue is the thermal management. Putting an optical component on the top of the LED engine increase the LED temperature that is causing additional light level drop. 

Q: What is the traceability of your measurements?

A: All our measurement instruments are traceably calibrated to the National Metrology Institute of Finland / USA, MIKES/NIST.

Q: Should I use your measurement services or purchase my own measurement setup?

A: It depends on your measurement need. In our laboratory we can make various types of measurements, we have a large capacity for big volumes and quick service. However,  if your measurement volume is extremely high and you need measurements often, it may be more cost efficient to purchase your own facility. Using our solutions you can build a very versatile laboratory.

Describe us your case, and we will help you to find the most suitable solution.

Q: What is photobiological safety and can you measure it?

Photobiology is the study of how optical radiation affects on living organisms. The photobiological safety means the light source not causing physical harm to eyes or skin. The standard EN62471 requires measurement of optical radiation between 200 and 3000 nm. 

Currently we can measure in the visible range 300 to 900 nm the UVA eye (315-400), the Retinal Blue-light (weighted 300-700) and the Retinal Blue-light-small-source (weighted 300-700). The so-called blue-light hazard is the most important safety parameter 

Q: How do I define the photometric measurement center of the luminaire?

A: The standard EN 13032-1:2004 defines the photometric center as follows:

Note! the center point for measurements is not the same as the point of the real photometric position. There is more discussion about this in the dissortation of the CEO Pasi Manninen.

The measured values are accurate only if the photometric center point is located on both the γ and C rotating axis. 

In the GPM Pro version of the measurement program there is an option to define the center point automatically.  

Q: What is the significance of the measurement distance?

A: The principle in the goniophotometric measurements is to handle the luminaire as a point source. The larger the measurement distance is compared to the dimensions of the luminaire, the better this assumption works.

The standard CIE S 025 defines the minimum ratio between the measurement distance / largest luminous dimension for different beam widths. These are indicative limits and the standard does not discuss too much about beam widths in different C planes as compared to the length and width parameter. There is some more discussion about this topic in the dissortation of the CEO Pasi Manninen.  

It is of great importance to measure the distance accurately, because inaccuracy in the distance causes two-fold inaccuracy in the illuminance level. The illuminance level on the photometer is inversely proportional to the square of the distance from the light source. Thus 1 % error in distance determination causes 2 % error in photometric values.

The GPM Pro version program automatically analyzes, whether the measurement distance is sufficient.

Q: Why is it important to attach the luminaire tightly on the goniometer?

A: If the geometry of the setup varies, i.e. the luminaire bends, the values close to the optical axis will not be measured. This may cause a big error both in the flux and the angular distribution.

The GPM program also makes automated/manual tests for checking whether the goniometer is properly aligned.

Q: What are UGR-values and how do I calculate them?

A: Unified Glare Rating (UGR) is an index to describe the physical glaring of the light. It is defined in the standard EN 12464-1. Our GPM Pro program defines the indices automatically.

Q: What is the luminous area of the luminaire? How do I define it?

A: Luminous area is the cross section area of the glowing parts of the luminaire seen from the direction of optical axis, and from the sides C0, C90, C180 and C270 (i.e. downwards, north, south, east and west). The luminous area is used in near field lighting simulations, simulation programs such as DIALux, defining luminance and UGR values.

It is measured using measuring tape (width by height) or optionally using the camera module and letting the GPM program define it automatically.

Q: How are the stabilization and the thermal drift taken into account?

A: In the GPM program there is an option to set the program to wait for stabilization of the luminaire. This can be done by setting the conditions manually, or by following the requirements of the standard LM 79-08. With the help of DC/AC power supply, the switching time can be synchronize for exact stability time / lumen drift measurement.

The drift is automatically measured during the measurement process. After the measurement, the program tells, if the requirements were met and the results are valid during the scanning of the angular luminous intensity distribution.

Q: I have a luminaire with light both downwards and upwards. How do I measure it?

A: Measure both the hemispheres (up and down), then combine them using the automatic tool on the GPM software. This can be done on individual files or on folders.

Q: The luminaire/optics were little tilted while I made the measurements. I would still like to get an ideal light distribution curve on my marketing material. How can I do it by your software?

A: In the GPM software there is a tool "symmetrize the beam". You can make the symmetrization either around C-axis (meaning the light distribution is rotationally symmetrical) or by C0-C180 and C90-C270 planes (meaning the light is symmetrical in "north and south" and "east and west").

However, if the luminaire is well attached, but dramatically tilted, the shape of the beam can be are corrected to nominal position in the GPM Pro version measurement program. 

Q: Using the SSL-products, is it possible to measure the effect of burning position and to correct it?

A: We have a solution to both questions. You can use the goniophotometer SSL G-200.2, which keeps the luminaire in vertical direction. Alternatively you can measure the luminaire using the horizontal-axis C-type goniometer and then measure the effect using an accessory. The GPM program will automatically measure a related BPC corrector factor and correct the results in a new photometric file.

You find more information about our solutions for this issue in the section CIE S 025 compliance.

Q: How do I measure the electrical parameters of the luminaire? What about power sources?

A: The GPM measurement program automatically reads the electrical values from the power meter combining the results with the photometricals. When using the AC source, the program switches the luminaire on and off thus enabling automatic measuring of stabilization.

The DC source is also operated by the GPM software. You can automatically measure the photometrical and color values of the luminaire on several DC current/voltage levels. 

Q: I am building a goniophotometer laboratory? What do I need? Can you help me?

A: At first you need a goniophotometer and a computer to operate it. The detector(s) can be chosen according to your need; photometer, colorimeter, spectrometer and luminance camera.

If you want to measure or control the electrical values, you need either power meter or a (AC or DC) source.

The walls, the floor, and the roof in laboratory room needs to be non-reflecting black to minimize the effect of the stray light on the measurements.

We can provide you all these. Plus the training!

Q: I have an existing meter/sphere. Can you modernize/modificate it?

A: Yes. We have done integrations of various meters to our systems, as well as modifications to fit a detector to an integrating sphere from other supplier. Just tell us your need!

You can see some examples of our tailored solutions

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