A light-providing device is provided, including a light guiding member, an LED (light-emitting diode), and a light distribution adjusting member, wherein the LED is disposed on the light guiding member. The light guiding member has an opening. The light distribution adjusting member has an inlet and an outlet. The inlet is connected to the opening. The shape or dimensions of the inlet is different from that of the outlet. A plurality of lights generated by the LED enter the light distribution adjusting member through the opening and the inlet, and leave the light distribution adjusting member through the outlet. The lights include a first light angular distribution at the inlet, and include a second light angular distribution at the outlet, wherein the second light angular distribution/the first light angular distribution is proportional to the inlet/the outlet.