Poste de luz vs. candeeiro de rua
The primary difference between poste de luz and candeeiro de rua is regional usage (Brazil vs. Portugal) and the literal focus of the word (the pole vs. the lamp fixture). While both describe street lighting, they are rarely interchangeable between the two main variants of the Portuguese language.
Poste de luz
A2This term is used almost exclusively in Brazilian Portuguese. It literally translates to post of light or light post. It emphasizes the physical infrastructure—the vertical concrete, wood, or metal pole—that supports the light fixture and electrical wires.
O carro perdeu o controle e bateu num poste de luz.
(The car lost control and hit a streetlight.)
A prefeitura precisa trocar a lâmpada daquele poste de luz.
(City hall needs to change the bulb on that light post.)
Ela estava esperando o ônibus encostada no poste de luz.
(She was waiting for the bus leaning against the streetlight.)
Candeeiro de rua
A2This is the standard term in European Portuguese (Portugal). It literally translates to street lamp. In Portugal, candeeiro is the general word for any lamp (table lamp, ceiling lamp), whereas in Brazil, candeeiro typically refers to an old-fashioned oil lamp or lantern.
A luz do candeeiro de rua entrava pela janela do quarto.
(The light from the street lamp came through the bedroom window.)
Os serviços municipais estão a reparar o candeeiro de rua em frente à loja.
(Municipal services are repairing the street lamp in front of the store.)
Era uma noite escura e apenas um candeeiro de rua estava aceso.
(It was a dark night and only one street lamp was lit.)
Summary
Use poste de luz if you are speaking Brazilian Portuguese; this term highlights the vertical pole structure. Use candeeiro de rua if you are speaking European Portuguese; this term uses the standard Portuguese word for a lamp fixture.