neru mae ni, heya no denki wo sukosi kuraku simasu.

When a verb comes before 前に, it normally stays in the dictionary form:

• 寝る前に = before sleeping / before I sleep
• 食べる前に = before eating
• 行く前に = before going

So 寝ます前に is not the normal pattern.
The grammar is:

• verb (dictionary form) + 前に

This is different from English, where we often use before + -ing.

前 means before or in front, and に marks the point in time.

In this sentence, 寝る前に means:

• before sleeping
• before I go to bed

So 前に is acting like a time expression.

You will often see:

• 食事の前に = before the meal
• 出かける前に = before going out
• 寝る前に = before sleeping

The comma is just there to make the sentence easier to read.

Japanese often puts a time phrase or context phrase first, like:

• 寝る前に、...
• 毎朝、...
• 学校で、...

The comma is helpful, but it is not always required.
You could also write:

• 寝る前に部屋の電気を少し暗くします。

That would still be natural.

Literally, it is something like the room’s light or the light in the room.

Here:

• 部屋 = room
• の = links nouns together
• 電気 = electric light / light / electricity, depending on context

So 部屋の電気 means the light associated with the room, usually understood as:

• the room light
• the lights in the room

In everyday Japanese, 電気 often means the light(s), not just electricity as an abstract idea.

The particle の connects nouns. It can show possession, association, location, type, and more.

In 部屋の電気, it means something like:

• the electric light of the room
• the room’s light
• the light in the room

So this is not only strict ownership. It is more like the light belonging to / associated with / located in the room.

Other examples:

• 日本の文化 = Japanese culture / the culture of Japan
• 学校の先生 = the school’s teacher / teacher at the school
• 台所の窓 = the kitchen window / the window in the kitchen

Because 電気 is the direct object of します here.

The speaker is doing something to the light:

• 電気を暗くします = make the light dark/dimmer

So を marks the thing being changed.

This is a very common pattern:

• 部屋をきれいにします = make the room clean
• 髪を短くします = make the hair short / cut the hair shorter
• 音を大きくします = make the sound louder

Because 暗い is an い-adjective, and when you use it with する to mean make something ..., it changes form:

• 暗い → 暗くする

This -く form is the adverb-like form of an い-adjective.

So:

• 部屋の電気を暗くします = make the room light dim/dark

More examples:

• 明るい → 明るくする = make bright
• 早い → 早くする = make earlier / do faster
• 小さい → 小さくする = make small

So the pattern is:

• object + い-adjective stem + くする

No. 暗くします means make it darker or dim it.

So the light is still on, just less bright.

If you want to say turn off the light, you would usually say:

• 電気を消します

So there is an important difference:

• 電気を暗くします = dim the light
• 電気を消します = turn off the light

少し means a little.

It modifies 暗くします, so the idea is:

• make it a little darker
• dim it a bit

Without 少し, the sentence would mean simply:

• I dim the room light
• I make the room light darker

With 少し, it sounds softer and more specific.

Because 少し is modifying the change: make it a little dark/dimmer.

So this order is natural:

• 電気を少し暗くします

You may also see adverbs placed in slightly different positions in Japanese, but this one is very standard and easy to understand.

Compare:

• 少し食べます = eat a little
• 少し待ちます = wait a little
• 少し暗くします = make it a little darker

します is the polite non-past form. In Japanese, the non-past can mean:

• a habitual action
• a future action
• a general practice

So depending on context, this sentence could mean:

• I dim the room light a little before going to bed.
  (habit / routine)

or

• I’ll dim the room light a little before going to bed.
  (future)

Japanese often leaves that distinction to context.

Yes. In many everyday contexts, 寝る can refer to actually sleeping or to going to bed.

So 寝る前に can naturally be understood as:

• before sleeping
• before I go to sleep
• before going to bed

The exact English wording depends on the situation, but the Japanese is normal either way.

Usually, 寝る前に is the more standard and natural form here.

You will sometimes see 前 used without に in certain expressions, but for learners, it is safest to remember:

• verb + 前に

So:

• 寝る前に = natural
• 食べる前に = natural
• 出かける前に = natural

Using に makes the time relationship clear.

It is describing the speaker’s action of changing the light.

That is an important difference:

• 電気が暗い = the light is dim
• 電気を暗くする = make the light dim

So in this sentence, the speaker is not just stating a condition. They are actively changing the brightness.

That is why する is used.