A planar light source, comprising: a light guide plate made of a light-guiding material; and a light-emitting diode light bar, comprising: a light bar substrate, which comprises an intermediate metal plate, a first side metal plate, and a second side metal plate, and defines a receiving space, wherein the first side metal plate is insulatingly attached to a first side surface of the intermediate metal plate, the second side metal plate is insulatingly attached to a second side surface of the intermediate metal plate, and the intermediate metal plate comprises a light-emitting surface; at least one bonding layer; at least one LED chip bonded to the light-emitting surface of the intermediate metal plate by the at least one bonding layer; at least one first wire coupled between a positive terminal of the at least one LED chip and the first side metal plate, and serving as an electroconductive path for the positive terminal of the at least one LED chip; at least one second wire coupled between a negative terminal of the at least one LED chip and the second side metal plate, and serving as an electroconductive path for the negative terminal of the at least one LED chip; and at least one package unit comprising fluorescent powders and a package material for packaging the at least one LED chip; wherein the LED light bar is disposed on a lateral side of the light guide plate, at least a portion of the receiving space of the LED light bar is embedded in the lateral side of the light guide plate, and the light guide plate directly contacts the at least one package unit. a light guide plate made of a light-guiding material; and a light-emitting diode light bar, comprising: a light bar substrate, which comprises an intermediate metal plate, a first side metal plate, and a second side metal plate, and defines a receiving space, wherein the first side metal plate is insulatingly attached to a first side surface of the intermediate metal plate, the second side metal plate is insulatingly attached to a second side surface of the intermediate metal plate, and the intermediate metal plate comprises a light-emitting surface; a light bar substrate, which comprises an intermediate metal plate, a first side metal plate, and a second side metal plate, and defines a receiving space, wherein the first side metal plate is insulatingly attached to a first side surface of the intermediate metal plate, the second side metal plate is insulatingly attached to a second side surface of the intermediate metal plate, and the intermediate metal plate comprises a light-emitting surface; at least one bonding layer; at least one LED chip bonded to the light-emitting surface of the intermediate metal plate by the at least one bonding layer; at least one first wire coupled between a positive terminal of the at least one LED chip and the first side metal plate, and serving as an electroconductive path for the positive terminal of the at least one LED chip; at least one second wire coupled between a negative terminal of the at least one LED chip and the second side metal plate, and serving as an electroconductive path for the negative terminal of the at least one LED chip; and at least one package unit comprising fluorescent powders and a package material for packaging the at least one LED chip; wherein the LED light bar is disposed on a lateral side of the light guide plate, at least a portion of the receiving space of the LED light bar is embedded in the lateral side of the light guide plate, and the light guide plate directly contacts the at least one package unit.