Luminance measurement using the Goniophotometer

Goniophotometer

Definition of a goniophotometer

A goniophotometer is a piece of equipment that will generate an IOS file. An IOS file three-dimensional bubble of the light source that we can give to our designers to do all their modding designs.

LM-79 Moving Detector Goniophotometer (Mirror Type C) AL

We have to fit the light. Square the light off. Get it levelled to the equipment.
•  This mirror will now rotate around, taking measurements where it is reflected off the mirror.
•  All the light is transferred from the mirror on the front to the mirror behind and comes down to the point where the photocell is located.
•  The photocell is situated at the end. As it rotates around, it changes the angle that the cell is viewing.
•  Now, physically getting a measurement from every point within that luminaire.

Benefits of a goniophotometer

The benefits of having a goniophotometer are numerous. Firstly, it gives a quick test around the time. Developing our new products within the lighting, we can design, modify, and retest for us to do that in an external test house.

Goniophotometers provide the measurement of luminous intensity distribution and total luminous flux. They are known best for measuring the total luminous flux of SSL products of relatively large size (corresponding to dimensions of traditional fluorescent lamp luminaires). On the other hand, they can also measure the small SSL products. In addition, a goniophotometer is installed in a dark room, normally temperature-controlled. It is not subject to the accumulation of heat from a source being measured.

A goniophotometer is usually used for the measurement of the emitted light. The whole setup features a mechanical goniophotometer with two horizontal and vertical axes. These axes are used for the rotation of the test sample. In addition, a photometer is used for the measurement of luminous intensity.

What is Luminance?

The luminance of a light-emitting object or surface is the luminous intensity emitted per unit of (apparent) area of that surface in a specific direction. The unit of luminance is known as candela per square meter.

Here are some examples which will help you understand luminance. Examples are the sun, the filament of a clear incandescent lamp, fluorescent lamp, and road surfaces under artificial lighting.

Luminance measurement

The source’s luminance is the ratio between the luminous intensity emitted in a direction and the apparent surface of the luminous source in the considered direction. Luminance is expressed in candelas by the square meter (cd/m2) or foot Lambert (fl).
•  Before starting to use the luminance meter, remove the protective covers from the front and back.
•  Switch on the device by sliding the power switch to ON.
•  By turning the focus ring, adjust the sharpness of the point, which needs to be measured.
•  Aim the meter at the point, pull the measuring trigger and hold it for a few seconds.
•  The TV screen is divided into three parts. Each part includes the 10 measured points. In the example, points 1,3,5,7 and 9 of the top part.
•  TV is at the end of the room under points 92-93. Luminance meter is 6m away from the TV under the points 20-21.
•  Luminance meters can measure the subjects as close as 1014 mm from the focal-point indication.
•  Let’s measure the 1st point of the upper part. New measurements will be taken, and the readings will be displayed every 0.8 to 1 sec at fast response speed and every 1.4 to 1.6 seconds at slow response speed. This would happen when the measuring trigger is held in.
•  Result would be 3.681 cd/m2.
•  Now, consider the 3rd point of the upper part. The fast response speed is used when metering under normal lighting conditions, including natural light and fluorescent lighting.
•  Result would be 16.05 cd/m2.
•  Now, consider the 5th point of the upper part.
•  The slow response speed is used when metering flickering light sources, including TV screens and monitors.
•  Result would be 47.75 cd/m2.
•  Now, consider the 7th point of the upper part. In this case, the result would be 101.8 cd/m2.
• Now, consider the 9th point of the upper part. In this case, the result would be 183.9 cd/m2.

Relation between illuminance and luminance

Illuminance is the quantity of light or luminous flux falling on a unit area of a surface. The unit of illuminance is lumen per square meter or lux. For example, summer at noon under a clear sky in the open under a heavily overcast sky, artificial light office and a full moon on a clear night.

In the case of a light-reflecting surface, the luminous intensity that the surface emits is usually not known, but the illuminance on the surface is often known. Illuminance is independent of the surface type, and it doesn’t matter if it’s a wall, floor, desk or table top, or anything else.

It only depends on the amount of light that falls on that surface. For a perfectly diffusing surface, a relationship exists between the illuminance on the surface, reflectance, and the surface’s luminance. Reflectance refers to the fraction of the incident light reflected from a surface.

Frequently Asked Questions

How does a goniophotometer work?

A goniophotometer is a photometric device used to measure the perceived power of a light source at different angles. It is mostly used for testing the luminous flux of directed light sources like LED and automotive headlights.

Which is better, a goniophotometer or an integrating sphere?

A goniophotometer will give you the same results as you get with an integrating sphere. But where is the dividing line? With a goniophotometer, you will achieve the angular distribution information too. On the other hand, the limitations for the luminaire (dimensions, mass) are way broader as compared to the goniometer.

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.

Our main products are Goniophotometer, Integrating Sphere, Spectroradiometer, Surge Generator, ESD Simulator Guns, EMI Receiver, EMC Test Equipment, Electrical Safety Tester, Environmental Chamber, Temperature Chamber, Climate Chamber, Thermal Chamber, Salt Spray Test, Dust Test Chamber, Waterproof Test, RoHS Test (EDXRF), Glow Wire Test and Needle Flame Test.

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