We are accustomed to the measurement results of the quantitative analysis of conventional physical quantities. Although the measurement instrument also has accuracy problems, the measurement error does not affect the application of the measurement data. The reason is that the instrument deviation of the conventional physical quantity is not large, and the measurement error can be ignored. However, the spectrum is negligible, but the measurement of the parameters needs attention. The deviation of the instrument plus the error of the measurement method will lead to large errors in the measurement data. The data error of the spectral parameters of the grow lights will cause a series of application problems, which need to be highly valued by us. Performing an error assessment may be the beginning of a series of errors.
Measurement error, deviation, accuracy
1. Error: refers to the difference between the measured result and the true value; although the measurement conditions is the best, the true value of the measured data is still difficult to test; there must be a difference between the measured value and the true value. The difference between the measured value and the true value is called the error; the smaller the error, the higher the accuracy of the data; the larger the error, the lower the accuracy of the data.
There is a basic rule here: the smaller the absolute value of the measured parameter, the more often the error is higher than the absolute value of the measured parameter.
2. Deviation: Deviation, also known as apparent error, refers to the difference between the measured value and the average value of the measurement. It can be used to measure the accuracy of the measurement results. The smaller the deviation, the higher the accuracy, and the better the consistency of the measurement.
3. Accuracy: Accuracy refers to the degree of conformity between the results of a sample multiple times, expressed as deviation; the greater the deviation, the lower the measurement accuracy.
The error and deviation are different for the object. In the actual measurement of the spectral data, in order to measure the true value of the spectral data, the average value of the multiple tests can be taken as the true value and the deviation as the error.
Three metering systems for photosynthesis active radiation (PAR)
Photosynthesis active radiation (PAR) is defined as optical radiation at wavelengths in the range of 400-700 nm and is available in three metering systems.
1. Optical system, a measure based on the visual response of the human eyes, expressed in illuminance (LX).
2. Energy system, measured by the radiant flux density (W/m2) of the PAR range.
3. Quantum systems, measured by the optical quantum flux density (PPFD) of the PAR range.
These three metering systems use different photoelectric sensors, which are: illuminance sensor, irradiance sensor, and light quantum sensor; at present, the spectral parameters of plant lights are mainly measured by quantum systems.
These three systems do not have a formula conversion relationship. When the spectral shape of the plant light is determined, there is a certain conversion factor.
We define the conversion factor of illuminance value (LX) and photon flux density (PPFD) as the XD conversion factor; for sunlight, the XD is 55-58; the XD factor can be accurately and reliably applied to plant light data measurement.
Measurement error of integrating sphere spectroscopic analysis system
The spectral parameters of the plant light are measured by the integrating sphere spectroscopic analysis system. For the integrating sphere spectroscopic analysis system, the standard lamp is used for initial calibration. The calibration benchmark and accuracy are very important. The benchmark has a large deviation, and the error of the test result is amplified. The calibration accuracy of the integrating sphere spectral analysis system directly affects the error value of the test results.
The results of testing the same light source on different manufacturers’ instruments are different. The deviation of the measurement data of LEDs of the same package specification is also large in different enterprises; the same LED is tested in several testers of the same specification, and the result will not be the same, these are the complexity of the spectral test, the evaluation of the integration sphere spectral measurement error can be considered from the following aspects.
The first thing that affects the spectral measurement error of the integrating sphere is the system calibration. The standard lamp calibration error cannot be eliminated and can only be minimized. The absolute error of calibration is usually more than 3%. Non-standard calibration methods sometimes show a 10% or absolute error.
The accuracy of the equipment accuracy of the integrating sphere spectrometry system is less than 5%, and the accuracy of the equipment is related to the price.
Secondly, the most influential measurement error is the test method. The error of the test method may reach more than 30%.
For the measurement of the LED, the LEDs in the integrating sphere are oriented differently, the test results are different, and the deviation is large.
LEDs with the same chip parameters have measurement deviations when the LED package has different illumination angles.
In addition, the measurement error also depends on the reflectivity of the inner surface of the integrating spherical Lambertian spherical reflecting cavity and the degree of aging of the surface coating; during the test, it is necessary to observe whether the dark current, the volatility, the operating temperature of the multiplier tube, etc. are in normal range or not.
The measurement error of the spectral parameters also depends on the control of the temperature of the test environment and the junction temperature of the measured light source.
The error of the above measurement data will affect the application and communication of plant lights. The spectral analysis of plant lights requires the operation of personnel with professional testing techniques. Usually we will see that the test results of the lamp bead package factory and the customer are different, the best solution is to conduct third-party test evaluation; increase the reliability of the parameters of the transaction; correctly understand the cause of the measurement error of the spectral parameters of the plant lights, which helps us to accurately evaluate the spectral parameters of the plant lights.
Usually, the absolute error and relative error of the integrating sphere spectroscopy system are used, and the measurement error caused by user error is between 8-20%.
LED plant light spectral parameter measurement attention points
It is necessary to pay attention to the measurement of the spectral parameters of the LED light bead and the light source composed of the lamp bead.
1. The lamp bead test requires professional testing of environmental specifications. The measurement error of the lamp bead is large, which may cause the source parameter to be unusable.
2. The company tries to use the measurement data of the light source composed of multiple lamp beads.
3. The measurement data of the lamp bead needs to evaluate the measurement error by comprehensive chip specifications, packaging materials, test conditions, etc.
4. The test process tries to simulate the thermal resistance of the lamp bead chip under actual working conditions.
5. The light source test is best measured with the actual drive used.
6. The LED plant light packaged in the rare earth process needs to be evaluated for the size of the blue shift.
The plant light is a spectral parameterized product. The planting process and environmental control require accurate spectral parameters to make basic calculation data. The measurement error is large, which directly affects the planting effect and needs sufficient attention.