## 3 Results
### Magnetized Construction Materials and Observatory Data Quality  
An example of observatory data contamination due to unwanted magnetic effects from poorly selected construction materials and devices is our experiment with LED lighting installation at the Klimovskaya magnetic observatory in 2018. This observatory has been constantly upgraded in order to provide proper conditions for the operation of magnetometers, as well as for an observer doing absolute declination (\(D\)) and inclination (\(I\)) measurements on a regular basis. The obtained absolute values are further used to calculate baseline values for vector fluxgate magnetometer data calibration and conversion of variation data to absolute components [3]. Therefore, the overall observatory data quality depends on the quality of the absolute measurements carried out manually in most observatories. In 2017, it was decided to improve the lighting in the absolute pavilion by changing a single light bulb above the DI magnetometer to something providing more light for more comfortable work. We had an idea to use a LED stripe fixed on the ceiling. This resulted in good lighting, but it was still not enough, as in some positions during the measurement, the limb was lightened only partially. Thus, a set of several similar LEDs on a plastic panel was mounted in early October 2018. This LED set can be seen in Figure 6a. Certainly, before the installation, the LED was tested to make sure that it was assembled from non-magnetic elements. However, after the LED set installation, the overall quality of the absolute measurements decreased, and the first evidence of it was the increased number of the measurements larger or smaller than the average trend. The resulting baselines were also poor in quality. Most of these inconvenient baseline values resulted from wrong declination measurements. Experimental total field measurements in the vicinity of the LED panel, carried out in November 2018 using the GSM-19 scalar magnetometer, indicated an increased geomagnetic field around the LED set. Therefore, LEDs were considered to be an unsuitable technical solution for geomagnetic observatories. The point is that being non-magnetic itself, a LED turns magnetic when turned on, as its current induces a magnetic effect. In December 2018, the LED lighting was replaced by 220 V AC halogen bulbs (Figure 6b). \begin{table}
\begin{tabular}{c c c} \hline
**Specimen** & **Magnetic Susceptibility, \(\times\)10\({}^{-5}\) SI** & **Conclusion** \\ \hline Andesite–basalt No. 1 & 540 & Medium magnetizable \\ Andesite–basalt No. 2 & 815 & Medium magnetizable \\ \hline \end{tabular}
\end{table} 
Table 6: Magnetic properties of igneous rocks at the Gyulagarak observatory location. The increased scatter of the \(D\) values corresponding to the period of measurements using LED lighting is seen even in Figure 7a; however, for a proper analysis, the \(D\) time series was detrended and plotted in Figure 7b. (the linear trend, excluded from the absolute \(D\) values for scatter analysis, is shown in Figure 7a with a red dashed line). Vertical purple dashed lines show the periods when the lighting in the pavilion was changed. Standard deviations \(\sigma_{D}\) for the detrended \(dD\) values for three analyzed periods shown in Figure 7 are given in Table 7. The largest standard deviation refers to period II when the  
Figure 6: Lighting in the absolute pavilion of the Klimovskaya magnetic observatory: (**a**) a LED set installed in October 2018; (**b**) halogen light bulbs installed in December 2018. Figure 7: Absolute \(D\) measurements for the period of 10 January 2018–1 May 2020 for different geomagnetic conditions in the absolute pavilion of the Klimovskaya observatory: (**a**) Initial \(D\) plot; (**b**) Detrended \(dD\) plot. Right axis on both plots refers to planetary \(Kp\) index graph superimposed on \(D\) and \(dD\) plots. LED set shown in Figure 6a was mounted above the DI magnetometer. This is a display of the impact of the magnetic field driven by the direct current of the LEDs on the DI sensor.