Learn Hardcore Indonesian: Lampu taman menyala otomatis setiap senja. - The garden lights turn on automatically every dusk.

menyala is the intransitive verb “to light up” or “to glow.” The root nyala can function as a noun (“light,” “glow”) or a bare verb. To show the lamp is doing the action itself, we add the active prefix meN-, which assimilates to meny- before ny-, yielding menyala. Without the prefix, nyala remains the root.

Why don’t we use menyalakan to say the lamps turn on?

menyalakan (prefix meN- + root nyala + suffix -kan) is the causative form “to turn something on” and requires an object. E.g., Petugas menyalakan lampu taman = “The staff turned on the garden lamps.” Here the lamps switch themselves on automatically, so we use the intransitive menyala.

What is otomatis, and why doesn’t it change form?

otomatis is a loanword (from English automatic) used as an adjective or adverb. In this sentence it functions as an adverb modifying menyala. Indonesian generally keeps such loanwords unchanged. For a more formal style you could say menyala secara otomatis, inserting secara (“in a/an … way”).

Why is it Lampu taman instead of Lampu di taman?