## 2 Investigation of Temperature Dependence of Current and Luminous Flux
The experimental dependencies of the relative values of the LED lamp is luminous flux \(F/F_{25}\) on the environment temperature \(T_{c}\) at 198 V, 220 V and 242 V supply voltages, where \(F_{25}\) is the value of the lamp luminous flux at +25 \({}^{\circ}\)C and 220 V supply voltage were shown in Figure 5.  
Figure 4: Dependencies of relative current values \(I_{inp}/I_{inp25}\) on temperature \(T_{c}\) at 198 V, 220 V and 242 V supply voltages for \(p=3\) W lamp. Figure 2.0 Dependencies of the relative values of the luminous flux \(F/F_{25}\) on \(T_{c}\) temperature at 198 V, 220 V and 242 V supply voltages for \(p=3\) W lamp. The dependence of voltage relative values \(U_{d}/U_{d25}\) on the LEDs of lamp on the environment temperature \(T_{c}\) at supply voltages 198 V, 220 V and 242 V, where \(U_{d25}\) is the voltage on LEDs at +25 \({}^{\circ}\)C and supply voltage of 220 V was shown in Figure 2.1 The value of the current through the LEDs was considered to be unchanged (Figure 4). As can be seen from the graphs shown in Figure 4, the linear driver circuit does not provide current stabilization when the supply voltage changes. But, at the same time, it is possible to observe the absence of current dependence on the temperature at different values of supply voltage. The change of luminous flux with temperature is significant (Figure 5) and within +15... +60 \({}^{\circ}\)C; temperature range at 198 V voltage is up to 8%, up to 13% at 220 V voltage, and up to 17% at 242 V voltage. That is, with the increase of current through LEDs relatively to its nominal value, the luminous flux drops increase. LedEX E27B lamp with power 6 W contains eleven SMD 2835 LEDs (nominal voltage 18 V, nominal current 30 mA, power 0.5 W, color temperature 4000 K) (in Figure 3b--the general view of the lamp without light diffuser). LEDs were connected gradually. The dependence of the current relative values \(I_{inp}/I_{inp25}\) for 6 W LED lamp on the environment temperature \(T_{c}\) at 198 V, 220 V and 242 V supply voltages was shown in Figure 7, and the dependence of the relative values of \(F/F_{25}\) luminous flux of the 6 W LED lamp on the environment temperature \(T_{c}\) at 198 V, 220 V and 242 V supply voltages was shown in Figure 2.2  
Figure 2.3 Dependencies of the relative voltage values \(U_{d}/U_{d25}\) of LEDs lamp on temperature \(T_{c}\) at 198 V, 220 V and 242 V supply voltages for \(p=3\) W lamp. Figure 2.4 Dependencies of the relative current values \(I_{inp}/I_{inp25}\) on \(T_{c}\) temperature at 198 V, 220 V and 242 V supply voltages for \(p=6\) W lamp. Dependencies of the relative voltage values \(U_{d}/U_{d25}\) of LEDs lamp with power 6 W on \(T_{c}\) environment temperature at supply voltages 198 V, 220 V and 242 V was shown in Figure 2.5  
If we compare dependencies that shown in Figures 4 and 7, we can see that if \(U_{AC}\) voltage changes by 10%, the input current of 6 W lamp changes twice as much as 3 W lamp and is more than 25%. This can be explained in the following way. The dependence of LEDs relative current change for LED lamp on the relative network voltage change can be written as follows [11; 16]  
Figure 2.6  
where \(\varepsilon L_{d}\) is relative current change through LEDs, \(\varepsilon U_{a}\) is a relative change in the amplitude of network voltage, \(U_{d}\) is voltage on LEDs. Figure 2.7  
If \(U_{d}\) value approaches to the value of the amplitude of the network voltage \(U_{a}\), the relative change in current through LEDs is sufficiently greater than the relative change of the network voltage. As in the case with 3 W lamp (Figure 4), the current of 6 W lamp (Figure 7) at different values of supply voltage practically does not change with temperature.