LED light flux test solution

LED light flux test solution

Luminous intensity luminous flux and spectral characteristics of LED and LED products

- Spectroradiometer

1. Basic concept of brightness and chroma

Luminous flux is the radiant power that can be felt by the human eye. The unit is: lumens (lm)

The luminous intensity is referred to as light intensity, the international unit is candela (candela) shorthand cd, other units have candlelight, branch light. 1cd or 1000mcd refers to the luminous flux emitted by a unit solid angle of light of a monochromatic light source (frequency 540X10^12HZ) in a given direction (radiation intensity in this direction is (1/683) watt/sphericity).

Brightness refers to the degree of brightness in a unit area, that is, the intensity of light per unit area. Unit: Candela (cd)

The irradiance refers to the radiant flux along the radiation direction, unit area, and unit solid angle.

Illuminance is the luminous flux received on the surface area of ​​the subject.

Irradiance refers to the amount of radiant energy projected per unit area per unit time.

The instrument for measuring the light intensity is called a photometer. After the light energy is converted into electric energy by a photocell, the relative value of the light is obtained by measuring the photocurrent value, and the light intensity value is obtained by calibration. It must be noted that due to the limitation of the spectrally sensitive region of the photovoltaic material (i.e., the probe) used in the phototube, the measured light intensity is only a value within the spectrally sensitive region. After measuring the light intensity using a photometer, it is easy to calculate the exposure amount because the exposure amount is equal to the product of the light intensity and the exposure time (exposure amount = light intensity X exposure time) in the case where the light intensity does not change with time.

Color temperature: When the absolute black body has the same characteristics as the spectrum of a certain light source at a certain absolute temperature, the specific temperature of the absolute black body is defined as the color temperature of the light source. The unit is: Kelvin (K). The color temperature is not the actual temperature of the light source itself, but a parameter used to characterize its spectral properties.

The concept of chromaticity includes: chromaticity coordinates, color temperature, dominant wavelength, and color purity. Usually, x, y or u, v chromaticity graphs are used, and any point on the chromaticity graph can represent a color. There is a color temperature curve on the chromaticity graph, and the color temperature at a nearby point on the color temperature curve is the correlated color temperature. There is a white spot E in the center of the chromaticity diagram. Assuming that there is another point B on the chromaticity diagram, connecting EB, and extending the EB and the line trajectory to point C, the wavelength corresponding to point C is the dominant wavelength of point B. The color purity is equal to the ratio of EB to EC length.

• At present, LED and LED lighting products can be divided into the following three types:

Low-power LEDs— classic injection molded or SMD packages

High-power LEDs - currently popular high-brightness package with thermal design

Solid-state lighting source ( SSL ) - a light source based on high-power LEDs

Various types of size power LEDs Solid State Light Source (SSL)

3. Different configurations can be adapted to the following optical parameter tests of different light sources:

Angle analysis of luminous flux through a goniometer

Total luminous flux test based on integrating sphere

Luminous intensity test based on inverse square law

The sensors tested may be a photometric detector, a tristimulus device, a spectroradiometer or an image luminance meter. The application of spectral analysis technology can learn more information about the device under test, which can effectively reduce the uncertainty of the test, because it directly adopts the color adaptation function. Therefore, this technology is becoming more and more important and has become one of the preferred methods for LED testing.

The current standards for testing LEDs are mainly for CIE 127:2007 for low-power LEDs and IES LM-79 for high-power LEDs and solid-state sources.

4.JET's LED light flux measurement solution

4.1 Measuring angular resolution luminous flux based on goniometer

The goniometer and the near-field goniometer are used to test the angular distribution of the LEDs (ie, the optical distribution curve - the angular distribution of the luminous intensity). This type of test takes a lot of time, but provides more comprehensive source data. The integral values ​​such as luminous flux and radiant flux will be calculated from the combination of the light distribution data. The color value should be calculated as the average of the entire solid angle (IES LM-79)

A common photometer or tristimulus value detector is used for this type of test. If additional testing of the spectral radiation distribution is required, a spectroradiometer such as the specbos 1211 can be used as a detector for the goniometer. Because of its high sensitivity, the test time for each step is short enough. The device can be equipped with a remote diffuser (fiber-expanded diffuser), so the configuration is very flexible.

Goniometer mit specbos 1211 Source: http://

4.2 Total luminous flux test based on integrating sphere

If you feel that the goniometer test is very slow and you only need to know the total integral value (production line application), then using the integrating sphere is a good choice. The integrating sphere consists of a minimum of two parts - one for the sample and the other for the detector. The detector is calibrated for radiant flux, but is essentially illuminating the inner surface of the ball. The integrating sphere should meet the following requirements to ensure that all surfaces have the same illuminance (the illuminance value of the test area will represent the illuminance value of the entire ball):

The ratio of the diameter of the probe interface to the diameter of the ball is at most 1:3;

Ignore the light self-absorption of the sample and sample interface or the auxiliary lamp;

The inner coating has a high reflection and diffusion coefficient (BaSO4);

Comply with other lumen test conditions as defined by CIE 127:2007 and IES LM-79;

There are three different integrating sphere test configurations depending on the standard:

2 π configuration: The sample is placed on the inner surface of the integrating sphere - it can be used for LEDs such that there is no reverse ray. Often used in single LEDs and LED arrays

4 π configuration: The sample passes through the interface and is placed inside the center of the integrating sphere—usually used for solid illumination sources. Auxiliary lamps must be used to compensate for light absorption from the sample and connector.

Part of the Luminous Flux Test Configuration: The sample is placed at a distance from the sample interface—a precise aperture is defined as a solid angle before the interface.

LEDs test geometry without back illumination (2π configuration)

The Specbos 1301 test system combines a specbos1201 with a 300mm diameter integrating sphere.

The specbos 1311/500 is a test system that combines a specbos1211 with a 500mm diameter integrating sphere and an auxiliary lamp. It can be used for 2 π and 4 π tests. For the 4π configuration, self-absorption calibration is necessary because the sample is placed entirely into the integrating sphere and therefore interferes with the optical path inside the integrating sphere.

Specbos 1301 (300 mm not hinged sphere) specbos 1311 (500 mm hinged sphere with auxiliary lamp)

Using the integrating sphere to measure LED luminous flux, LED mounting brackets need to be selected according to the package size and type of LEDs. The Specbos 1301 Luminous Flux Test System is compatible with Gooch & Housego brackets. Choosing the right LED mounting bracket requires the following requirements:

Easy to install and fix LED position

Mount the LED on the corresponding mechanical shaft

The distance between the light source and the detector can be set

Can reduce the shading effect of the bracket and the clip

Can also reduce the reflection of radiated light

4.3 Luminous intensity test based on the inverse square law

CIE decided to use new terminology to describe LED light intensity for LED measurement. The new term is called average LED intensity. (Average LED light intensity or average LED radiation intensity).

CIE standard conditions A and B for LEDs measurements. For the average LED intensity determined under these conditions, the symbols ILED A and /LED B are recommended. For both conditions, a detector with an annular inlet opening having a hole area of ​​100 mm2 (i.e., 11.3 mm in diameter) is used. To place the LED facing the detector, the distance between the conditions A and B is the distance between the LED and the detector, which are:

For CIE standard conditions A: 316 mm; for CIE standard conditions B: 100 mm.

For illumination, if the detector has been calibrated, the average LED intensity can be calculated from the following relationship:

ILED v = EV · d2

Here EV is the average illuminance measured by lx, and d is the distance in m. For condition A, d = 0.316 m, for condition B, d = 0.100 m.

These conditions correspond to the viewing angles of 0.001 sr (condition A) and 0.01 sr (condition B), but the actual dimensions are as important as the angles in the confirmed matching results. The equal angles are approximately 2° (condition A) and 6, 5° (condition B).

The Jeti 1401 is a visible light spectroradiometer that measures the average intensity of LED illumination according to CIE Section 127.

This product uses a test tube according to CIE-127 A/B condition, and the A/B condition can be switched freely. The mature software design is used to combine the luminous intensity, brightness and illumination of the LED. It is a multifunctional spectroradiometer.

The detector for this test can be a brightness sensor, a tristimulus value tester, a spectroradiometer or an imaging luminance meter.

The luminescence intensity (cd) test is usually calculated by the illuminance test. It can be tested by the settings described in CIE 127:2007. The idea behind these settings is that the sample can be adjusted by adjusting the mechanical settings—the test distance can be adjusted by adjusting the LEDs, and the angle can be adjusted with some mechanical axes.

CIE 127:2007 Condition A

The test result is considered to be the average intensity of the LED rather than the luminous intensity because it is not necessarily the maximum value of the LED.

The specbos 1401 uses the basic specbos1201 with test tubes and an integrating sphere that conforms to CIE127:2007. Two test distances (Condition A-316mm and Condition B-100mm).

Specbos 1401 condition B

If the brightness of CIE 127 is not achievable, the test can be used to achieve an optical platform illuminometer (Re: Radiant Intensity Calculation using Irradiance Measurement)

The separate specbos1201/1211 spectroradiometer combined software can also be used to measure LED brightness, irradiance, illuminance, irradiance, spectral characteristic curve, color temperature, chromaticity coordinates, color purity and other parameters, and quickly measure the data.

The spectral characteristics are the physical quantities directly tested by the device, and the remaining luminance chromaticities are based on this calculation.

In the spectral window, the user can see the wavelength distribution of the illuminant and analyze it.

By clicking on a wavelength, the software will display the spectral radiance of the source at that wavelength.

You can focus on a certain wavelength by setting the wavelength range.