A planar light source , comprising: a light guide plate made of a light-guiding material; and a light-emitting diode (LED) 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 (LED) 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 . <EOS>