Efficiency Improvement and Parameter Checkout of Emission Sources of Irradiation Equipment in Agriculture
Fluorescent lamps, xenon tube lamps, high-pressure sodium lamps, metal halide lamps and high-pressure mercury lamps with corrected chromaticity are used as light sources for plant photoculture. Their radiation utilization factors of PAR are up to 30%. As a result of analysis of the influence of the spectral composition on the growth and development of plants to determine the justified requirements for the spectrum of emitting lamps, it was found that the best results for industrial technology, depending on the plant variety, are provided by a spectral ratio of illumination in the blue, green, red areas Eb : Eg : Er = (10–30)% : (15–45)% : (40–75)%. The emission sources with a high utilization factor contribute to the growth of crop yields; semiconductor devices with RGB modules have come into use for this purpose.
Recently, many researchers propose to apply illumination systems in accordance with the function of spectral sensitivity of the poultry visual organ to illuminate poultry farms . The analysis of the studies conducted in the conditions of commercial chicken breeding revealed an improvement in the productive parameters of the experimental group of growing poultry of the parent flock Ross‑308 within 10% with blue-green LED illumination combined with ultraviolet irradiation in general illumination with LB‑40 type fluorescent lamps in comparison with the indicators of the control group, illuminated by LB‑40 type luminescent lamps.
In order to assess the degree of coincidence of the maxima of the spectral range of light sources and the relative spectral sensitivity of the poultry visual organ and the plant, it is necessary to apply a sufficiently accurate measurement technique. According to paragraph 220.127.116.11 of the USSR STATE STANDART 8.749–2011, for monochromatic (non-white) LEDs, the spectral mismatch errors may be larger due to the fact that some LED spectra reach their peaks at the ends of the function V(λ), which can greatly influence the measurement error . The spectral radiometers can be used for obtaining the spectral characteristics of light sources.
In the laboratory of the Common Use Center of the Light Engineering Faculty of the Federal State Budgetary Educational Institution of Higher Education "N. P. Ogarev Mordovia State University", the spectral characteristics of the LEDs were studied by spectral radiometers of two models, OL770 and Specbos1211, to determine the accuracy of the measurements, during which the absolute and relative measurement errors were determined.
Specbos 1211 is a compact high-sensitivity general-purpose spectral radiometer covering the range of waves from near ultraviolet to infrared radiation. The optical system of OL770 spectral radiometer consists of a narrow entrance slit and a concave diffraction grating that forms a flat focal surface. A multi-element photodetector, in the form of a silicon CCD matrix, is located in the focal surface. The device operates in the wavelength range of 380–1100 nm.
The spectral radiometer data were used to measure the emitting characteristics of the LEDs. The spectral radiometer and LED light sources were fixed on a photometric bench in a stationary position during measurement cycle; the center of the photodetector was on a straight line passing through the light center of the light source; the surface of the spectral radiometer was perpendicular to this line. The measurements of the LEDs were carried out with the following electrical parameters: I = 40 mA, U = 3.5 V. The ambient temperature was constant throughout the experiment. The time interval between the power supply to the LED and the actual measurements was 20 minutes, during which the light parameters were stabilized.
In determining the absolute and relative errors for actual values, the values obtained by the spectral radiometer OL770 were taken. This was done for the following reasons. First, the spectral resolution of OL770 device (0.75 nm) is higher than the analogous parameter of Specbos1211 device (4.5 nm). Second, the temperature of the photodetector in OL770 during the whole measurement process remains constant (–10 °C), which is due to the use of the Peltier element. Thus, the error caused by the dependence of the photocurrent of the receiver on the ambient temperature in OL770 device is absent.
During the study of the spectral characteristics of light-emitting diodes, a slight discrepancy of the wavelength maxima was revealed when measured by the spectral radiometers OL770 and Specbos 1211, respectively: green – 515 and 519 nm, red – 639 and 638 nm. For a blue LED, a maximum at a wavelength of 465 nm was shown by spectral radiometers.
The average relative error of the spectral power of radiation when measured by spectral radiometers relative to each other was 1% for a red LED, 5.5% for a blue LED, 4.5% for a green LED. The average relative error in measuring the spectral distribution of the radiation power of light-emitting diodes by the spectral radiometers OL770 and Specbos1211 was about 5%, which indicates a sufficient accuracy of the measurement by these devices. The obtained spectral characteristics were used in the modeling and designing of semiconductor light devices.
In accordance with the sensitivity curve of the visual organ of a human and poultry and that of the plants, the spectral coefficients for the use of radiation from various light sources, as well as combined instruments and installations using LEDs were calculated using the following formula:
where i is the corresponding spectral ranges of optical radiation.
To obtain estimates of the light sources utilization factors, as well as combined devices and installations using LEDs for various bioobjects, a program for modeling spectral characteristics was developed and tested in practical examples .
Luminescent lamps of LB, LD types and discharge lamps of DRI, DNaT, DRL types (see Fig.) were taken as the tested light sources. The results of the calculation of the utilization factors are given in Tables 1–3.
For traditional light sources, according to the function of the relative spectral luminous efficacy, the highest utilization factor is found in LB‑36 lamps and is 50%. The highest radiation utilization factor for the poultry visual organ is observed in lamps of LD‑36 type and is 56%. A high utilization factor of about 52% is observed for a combined installation using LB‑36 type lamps, LE‑15 type ultraviolet lamps and a module with blue and green LEDs .
The utilization factors for traditional light sources, determined from the relative spectral efficiency of plant photosynthesis, do not exceed 29%. In this regard, it is promising to increase the utilization factor by using red LEDs in combination with LD‑36, which allows to increase the utilization factor up to 42%.
In natural conditions, the poultry is under natural solar radiation, which includes the entire optical range of radiation according to USSR STATE STANDART 54164–2010.
The radiation spectrum of the cloudy and cloudless sky is distinguished. The calculated values of the radiation utilization factor for functioning of relative spectral sensitivity of visual organ (FRSSVO) of poultry in the cloudless sky in the wavelength range from 400 to 640 nm was 63%, in the sky covered with dense clouds in the wavelength range from 400 to 640 nm was 65%, in daylight in the wavelength range from 375 to 725 nm was 49%, solar radiation in the wavelength range from 330 to 780 nm was 40%.
Based on the calculated values of the radiation utilization factor, a prototype of the irradiation equipment was constructed, including blue-green LEDs and 2 erythemal lamps of LE‑15 type. This prototype was used as a local irradiation in general illumination with fluorescent lamps of LB‑36 type in the poultry farm for the growing poultry of the parent flock Ross‑308. These studies showed that with combined blue-green LED lighting in conjunction with ultraviolet irradiation in general illumination of luminescent lamps of LB‑40 type of the growing poultry of the parent flock Ross‑308, the performance of growing poultry is improved within 10% in comparison with traditional fluorescent lamps of LB‑40 type.
Thus, it has been experimentally confirmed that the control of the radiation utilization factor of various bioobjects plays a major role in selecting promising light sources for agriculture. And, in order to improve the efficiency of irradiators and plants, combined emission sources must be used.