8 common LED lamps and lanterns optical parameters testing techniques

1, photometric determination

The intensity of light, that is, the intensity of light, is the amount of light emitted at a certain angle. cie127 standard, the light-emitting diode due to the light is more concentrated, the inverse square law does not apply, cie127 on the measurement of light intensity proposed measurement conditions A (far-field conditions), measurement conditions B (near-field conditions) two kinds of measurement of the average normal light intensity conditions, 2 conditions are 1cm2. generally speaking, the Luminous intensity is measured with standard condition B.

2, luminous flux and luminous efficiency detection

Luminous flux is the sum of the amount of light emitted by the light source, that is, the amount of luminescence. Test methods are mainly the following two.

(1) integrated method

And in the integration ball in turn lit standard lamp and the measured lamp, in the photoelectric converter readings Es and ED. known standard light source flux Φ s, the measured lamp flux Φ D = ED × Φ s/Es. integration method using the "point light source" principle, simple operation, but by the standard and the measured lamp color temperature deviation, the measurement error is larger.

(2) Spectral method

The spectral energy P (λ) distribution is used to calculate the luminous flux. Using a monochromator, the 380 nm ~ 780 nm spectrum of the lamp is measured in the integrating sphere, and then the spectrum of the measured light is measured under the same conditions, and the luminous flux of the lamp under test is calculated by comparison.

Luminous efficiency is a light source emitted by the luminous flux and the ratio of power consumption, often using a constant current way to measure the luminous efficiency of LED.

3、Spectral characteristics detection

The spectral characteristics of the test includes spectral power distribution, color coordinates, color temperature, color rendering index and other content.

Spectral power distribution represents the light of the light source is made of a variety of wavelengths of color radiation group, each wavelength of radiation power size is also different, this different with the order of wavelengths is known as the spectral power distribution of the light source. The spectrophotometer (monochromator) and the standard lamp for the light source to compare the measurement and obtained.

The color coordinates are the number of luminous colors of the light source expressed numerically on a coordinate chart. There are many different coordinate systems for color coordinates, and the X, Y coordinate system is commonly used.

Color temperature is a representation of the amount of light source color table (appearance of color) that a person sees. A light source emits light that is the same color as the light emitted by a black body at a certain temperature, it is the color temperature. Color temperature in light is an important parameter to describe the optical properties of a light source. The theory related to color temperature originates from blackbody radiation, which can be obtained from the color coordinates containing the blackbody trajectory through the color coordinates of the light source.

Color rendering index indicates the amount of light emitted by the light source to correctly reflect the color of the illuminated object, usually expressed in Ra, Ra is the arithmetic mean of the color rendering index of the light source for eight color samples. Color rendering index is an important indicator of the quality of the light source, which determines the application range of the light source, improve the color rendering index of white LED is an important issue in the research and development of LED.

4, intensity distribution measurement

Light intensity with the spatial angle (direction) of the changing relationship is called the pseudo-intensity distribution, the closed curve connected by this distribution is called the light intensity distribution curve. Because there are more measurement points, each point is subject to data processing, generally using automatic distribution photometer for measurement.

5, the effect of temperature on the optical properties of LEDs

Temperature has an impact on the optical properties of LEDs. Many experiments have shown that the temperature has an effect on the emission spectrum and color coordinates of LEDs.

6, ground brightness measurement

The luminance of a light source in a certain direction is the luminous intensity per unit projection area in that direction, generally using surface luminance meter, aiming luminance meter to measure the surface luminance, there are 2 parts of aiming light path and measuring light path.

Part 2

LED lamp other performance parameters of the determination

1、Measurement of LED lamp electrical parameters

LED lamp electrical parameters mainly include positive, negative and negative three electrical parameters, which are related to the normal operation of the LED lamp and are one of the bases for judging the basic performance of the LED lamp. There are two ways to measure the electrical parameters of LED lights: one is a certain current, the second is to measure the voltage parameters; the second is to measure the current parameters when there is a certain voltage. Take the following measures.

(1) forward voltage

Apply a positive current to the tested LED lamp, the LED lamp will produce a voltage drop across the ends. By adjusting the current value determined by the power supply, record the corresponding reading on the DC voltmeter, that is, the forward voltage of the LED lamp. According to the relevant common sense, the LED positive conduction when the resistance is small, using the ammeter external method more.

(2) reverse current

Apply reverse voltage to the test LED lamp, adjust the voltage regulator, the amperometer reading for the reverse current of the LED lamp under test. As the LED reverse conduction resistance is larger, so use the ammeter internal method to measure the forward voltage of the LED.

2, LED tube thermal characteristics test

The thermal characteristics of the light-emitting diode has an important impact on the optical and electrical properties of the LED. Thermal resistance and junction temperature are the main thermal characteristics of LED2. Thermal resistance is the thermal resistance of the PN junction to the surface of the shell, i.e., the ratio of the temperature difference on the heat flow channel to the power dissipated on the channel, and junction temperature is the junction temperature of the LED.

LED junction temperature and thermal resistance are generally measured by: infrared microimage method, spectroscopy, electrical parameters, photo-thermal resistance, etc. Using infrared temperature microscopy or micro thermocouple, the temperature of the LED chip surface temperature measurement, the accuracy is not enough.

The current widely used electrical parameter method is to use the positive voltage drop and PN junction temperature into a linear relationship, using the LEDPN junction forward voltage drop difference to obtain the LED junction temperature.