Learn Hardcore Japanese: zitensya ni raito wo tukemasu.

In this sentence, に marks the target or location where you attach something. It’s like saying “to” or “onto” in English: “attach a light to the bicycle.”

Why is ライト written in katakana?

ライト is a loanword from English (light), so it’s written in katakana. Native Japanese words typically use kanji or hiragana, while foreign borrowings use katakana.

Why does ライト take the particle を instead of に?

The particle を marks the direct object—the thing being directly affected by the verb. Here, the light is what you’re attaching, so it takes を. Meanwhile, に marks the place or object you attach to (the bicycle).

What kind of verb is 付けます, and how is it different from 付く?

付けます is the polite form of the transitive verb 付ける (“to attach” or “to install”). Its intransitive counterpart is 付く, which means “to be attached” or “to stick.” Because someone is doing the attaching in this sentence, you need the transitive 付ける.

Why is the subject (for example, 私) omitted here?

Japanese often omits the subject when it’s obvious from context. In everyday speech, if it’s clear who’s doing the action, you don’t need to say 私 (“I”).

Could I reorder the sentence to ライトを自転車に付けます?

Yes. Japanese word order is flexible as long as you keep the particles. ライトを自転車に付けます still clearly means “I attach a light to the bicycle.”

What’s the difference between 付ける and 取り付ける?

付ける is a general verb for “attach” or “fix on.” 取り付ける (often written 取付ける) carries a nuance of installing or mounting—often more formal or technical. They overlap, but 取り付ける can sound more official.

Why is 付けます in the polite form? How would I express this casually?

付けます uses the polite –ます ending, which is common in formal situations or with people you’re not close to. In casual speech among friends, you’d use the plain form:
自転車にライトを付ける。