rantan ha akarui.

は is the topic marker. It tells you what the sentence is about.

So in ランタン は 明るい。, the topic is ランタン (lantern), and the sentence says something about it: it is bright.

A natural way to think about it is:

• As for the lantern, it is bright.

Even though は is written with the hiragana ha, here it is pronounced wa.

ランタン is written in katakana because it is a loanword or foreign-derived word in Japanese. Katakana is commonly used for:

• borrowed words
• foreign names
• sound effects
• emphasis in some cases

Here, ランタン comes from lantern. A learner should notice that many English-based words in Japanese are written this way, though their pronunciation is adapted to Japanese sound patterns.

明るい is an i-adjective.

In Japanese, there are two major adjective types:

• i-adjectives: words ending in い
• na-adjectives: words that need な before a noun

明るい means bright and belongs to the first group. Because it is an i-adjective, it can directly end a sentence:

• ランタン は 明るい。 = The lantern is bright.

You do not need a separate word for is after it in plain form.

Because 明るい already functions as the predicate of the sentence.

In English, we say:

• The lantern is bright.

But in Japanese, i-adjectives can finish the sentence by themselves:

• ランタン は 明るい。

So this is a complete sentence. Japanese does not need a separate is here.

If you want to make it polite, you can add です:

• ランタンは明るいです。

Yes, it is correct and more polite.

Compare:

• ランタンは明るい。 → plain style
• ランタンは明るいです。 → polite style

Both mean the same thing. The difference is tone and formality.

Although it is written は, when used as the topic particle, it is pronounced わ.

So:

• ランタン は 明るい is pronounced roughly like
• rantan wa akarui

This is one of the first pronunciation exceptions learners meet in Japanese.

Sometimes yes, but the nuance changes.

• ランタンは明るい。 → As for the lantern, it is bright.
• ランタンが明るい。 → The lantern is the one that is bright / It is the lantern that is bright.

は presents ランタン as the topic. が more strongly identifies or focuses on ランタン as the subject.

In many basic situations, は is the more neutral choice if you are simply describing the lantern.

It can describe more than just physical brightness.

Common uses of 明るい include:

• bright light / a bright object
• a cheerful personality
• a bright atmosphere
• sometimes knowledgeable about something, depending on context

In ランタンは明るい。, the meaning is the literal one: the lantern gives strong light or is bright.

The spaces are probably just for learners.

Normal Japanese writing usually does not use spaces between words:

• ランタンは明るい。

Teaching materials often insert spaces to make sentence structure easier to see:

• ランタン　は　明るい。

So the spaced version is helpful for study, but not standard everyday writing.

It is grammatically correct and easy to understand.

That said, in real conversation, Japanese speakers might often say something a little more natural depending on context, such as:

• このランタンは明るい。 = This lantern is bright.
• このランタン、明るいね。 = This lantern is bright, isn’t it?

Without context, ランタンは明るい。 can sound a little textbook-like, but it is still a perfectly good example sentence.

You change the i-adjective 明るい to its negative form:

• ランタンは明るくない。 = The lantern is not bright.

Polite version:

• ランタンは明るくないです。
• ランタンは明るくありません。

This is a useful pattern for i-adjectives:

• 〜い → 〜くない

So:

• 明るい → 明るくない

For an i-adjective, the past form is made like this:

• 明るい → 明るかった

So:

• ランタンは明るかった。 = The lantern was bright.

Negative past:

• ランタンは明るくなかった。 = The lantern was not bright.

This is a very common i-adjective pattern to learn early.