## 3 Results  
Investigation of Temperature Characteristics of smd2835 LEDs When LEDs Are Powered by a Rectangular Pulsed Voltage  
The electrical parameters and luminous flux of the LEDs were studied when the ambient temperature varied for different values of the current and voltage and when they were powered by a pulsed voltage. The effective value of the LED current \(I_{d}\)_imp_ was set so that the illuminance was equal to the illuminance created by the nominal value of its current \(I_{d\text{ }nm}\). The LEDs were powered by a constant voltage source at a temperature of 25 \({}^{\circ}\)C. In this case, the luminous fluxes of LEDs will also be equal, and the average values of the LED current will be the same since the luminous flux and brightness are proportional to the average value of the LED current [12; 13]. In order to ensure the same luminous flux for different values of the pulse duty cycle D, the LED voltage and current should be as follows:  
* For \(D=0.5\), the effective voltage value \(U_{d\text{ }imp}\) will be equal to \[U_{d\text{ }imp}=U_{d\text{ }nom}/k_{a}=U_{d\text{ }nom}/1.41=0.71\times U_{d\text{ }nom},\] (2) where \(U_{d\text{ }nom}\) is the LED nominal voltage, \(k_{a}\) is the amplitude factor, \(I_{d\text{ }imp}\) is the effective current value. \[I_{d\text{ }imp}=I_{m\text{ }imp}/k_{a}=2\times I_{d\text{ }nom}/1.41=1.41\times I_{d\text{ }nom},\] (3) where \(I_{m\text{ }imp}\) is the amplitude value of the current, and \(I_{d\text{ }nom}\) is the rated current of the LED. * For \(D=0.33\), the effective voltage value \(U_{d\text{ }imp}\) will be equal to \[U_{d\text{ }imp}\ =\ U_{d\text{ }nom}/k_{a}=U_{d\text{ }nom}/\sqrt{3.03}\ =\ 0.58\ \times\ U_{d\text{ }nom}\] (4) \(I_{d\text{ }imp}\) is the effective current value; \[I_{d\text{ }imp}=I_{m\text{ }imp}/k_{a}=3.03\ \times\ I_{d\text{ }nom}/\sqrt{3.03}\ =\ 1.74\ \times\ I_{d\text{ }nom}.\] (5)
* The LED pulse voltage was maintained as constant at a value equal to that at a temperature of 25 \({}^{\circ}\)C, and when the temperature changed, the LED current values were measured along with the illumination generated by it. In both cases, the illumination was set as equal to that generated by the rated current of the LEDs powered by a constant voltage source at a temperature of 25 \({}^{\circ}\)C.  
We present the characteristics of smd2835 LEDs with a rated voltage of 18.5 V, a power of 1 W, a rated current of 50 mA, and a color temperature of 3300 K [23, 24, 25] when the LED is powered by rectangular pulses with a frequency of 20 kHz. The obtained temperature dependence in relative units at \(D=0.33\) (\(D=1/3\)) is shown in Figures 2 and 3, where \(I_{d\;imp}\) is the value of the current, \(U_{d\;imp}\) is the voltage, \(\Phi_{imp}\) is the luminous flux, and \(I_{d\;imp25^{\circ}}\)C, \(U_{d\;imp25^{\circ}}\)C, and \(\Phi_{imp25^{\circ}}\)C are, respectively, the LED current, voltage, and luminous flux at an ambient temperature \(T_{c}=25\)\({}^{\circ}\)C.  
We can analyze the graphs shown in Figure 2. With \(I_{d\;imp25^{\circ}}\)C = 80 mA = const, the luminous flux is equal to the nominal luminous flux when the LED is powered by a constant  
Figure 3: Temperature dependence in relative units of the LED voltage, current, and luminous flux for the pulse voltage at \(D=0.33\) at a constant voltage value. Figure 2: Temperature dependences in relative units of voltage, current, and luminous flux of the LED for a pulse voltage at \(D=0.33\) with a constant current value. voltage source. In this case, the LED voltage decreases with an increase in temperature by 4%. The luminous flux decreases significantly to 12% at 60 \({}^{\circ}\)C versus its value at 25 \({}^{\circ}\)C.  
With a constant value of the forward voltage \(U_{d\,imp25^{\circ}\text{C}}=\text{const}\) (Figure 3), the current increases with a temperature up to 12% at \(T_{c}=\) 60 \({}^{\circ}\)C, and the decrease in luminous flux in the temperature range from 20 to 60 \({}^{\circ}\)C is not more than 6%. We compare the dependencies presented in Figures 2 and 3.