light sensing signal ps for the control module 50 to refer and elevate or lower the elevator module 30 accordingly referring to fig8 the control module 50 having the light sensor 52 is able to perform the following steps acquiring a light sensing signal s 50 generating a control signal s 60 elevating or lowering the elevator module according to the control signal s 70 and switching the lighting displaying module into the illumination mode or the display mode s 80 in the step of acquiring the light sensing signal s 50 referring to fig7 the light sensor 52 of the control module 50 serves to generate the light sensing signal ps by detecting the intensity of ambient sunlight for example when sunlight is sufficient the light sensing signal ps has a high value and when sunlight is insufficient the light sensing signal ps has a low value in the step of generating the control signal s 60 the control module 50 generates the control signal ctrl according to the light sensing signal ps for example when the light sensing signal ps is higher than a preset threshold it is indicated that sunlight is sufficient and no additional illumination is needed thus the control signal ctrl generated by the control module 50 makes the elevator module 30 lower to the second location 24 on the contrary when the.