Bisogna spegnere la luce prima di uscire di casa.

Bisogna comes from bisognare, and in this kind of sentence it is an impersonal verb. It means something like it is necessary, one must, or you have to in a general sense.

So:

• Bisogna spegnere la luce = It is necessary to turn off the light
• more naturally in English: You have to turn off the light / One must turn off the light

It is called impersonal because it does not refer to a specific person. It expresses a general rule or necessity.

After bisogna, Italian normally uses an infinitive to say what action is necessary.

Pattern:

• bisogna + infinitive

Examples:

• Bisogna studiare. = It is necessary to study.
• Bisogna aspettare. = You have to wait.
• Bisogna spegnere la luce. = You have to turn off the light.

So spegnere stays in the infinitive because it is the action required by bisogna.

In Italian, articles are used more often than in English. Here la luce means the light, referring to the light in the house or room in a general practical sense.

Italian often says:

• accendere la luce = turn on the light
• spegnere la luce = turn off the light

Even where English might sometimes say turn off lights or speak more generally, Italian commonly uses the singular expression la luce.

Spegnere means to switch off, to turn off, or more generally to extinguish.

It can be used for different things:

• spegnere la luce = turn off the light
• spegnere il computer = turn off the computer
• spegnere il fuoco = put out the fire

So in this sentence it specifically means to turn off.

In Italian, when prima is followed by a verb, you usually use di + infinitive.

So:

• prima di uscire = before leaving / before going out

This is a very common structure:

• prima di partire = before leaving
• prima di mangiare = before eating
• prima di dormire = before sleeping

Without di, the sentence would be ungrammatical here.

Uscire di casa means to leave the house/home or to go out of the house/home.

Here di means something like from/out of.

This expression is very common in Italian:

• uscire di casa = leave home / leave the house
• essere fuori casa = be away from home

In English, we often do not say every part literally. A more natural English translation may just be before leaving the house or before going out.

Italian often omits the article with casa in certain common expressions, especially when casa means home rather than a specific physical building.

For example:

• sono a casa = I am at home
• vado a casa = I am going home
• esco di casa = I leave home
• torno a casa = I return home

If you say della casa, that would sound more like of the house in a more specific, literal sense, which is not what is meant here.

Yes, many learners will notice both forms. Uscire di casa is a very common fixed expression, especially in standard usage meaning to leave home. Uscire da casa can also be heard and understood.

Very roughly:

• uscire di casa often sounds like the established expression leave home
• uscire da casa can sound a little more literally like go out from the house

In everyday Italian, both may appear, but uscire di casa is a very common and natural phrase.

Not exactly.

• bisogna = it is necessary / one must / you have to in a general sense
• devi = you must when speaking directly to one person
• deve = he/she must, or you must in a formal singular form

Compare:

• Bisogna spegnere la luce. = One must / You have to turn off the light.
  
  • This sounds general, like a rule.
• Devi spegnere la luce. = You must turn off the light.
  
  • This is directly addressed to someone.

So bisogna is less personal and more general.

The order is very natural in Italian:

1. Bisogna = the general necessity
2. spegnere la luce = the required action
3. prima di uscire di casa = the time expression, saying when

Italian often puts the main idea first and then adds the time phrase. You could move parts around for emphasis, but this order is the most straightforward and neutral.

Yes. Depending on context, English may translate it in slightly different ways:

• before leaving the house
• before going out
• before leaving home

The Italian phrase covers that idea naturally. The exact English wording depends on what sounds most natural in context.

These two words often cause pronunciation questions.

• spegnere: the gn sound is like the ny sound in canyon
  
  • roughly: speh-nye-re
• bisogna: again, gn sounds like ny
  • roughly: bee-zon-ya

So:

• bisogna ≈ bee-ZON-ya
• spegnere ≈ SPEH-nye-re

That gn sound is very important in Italian and is not pronounced like a hard English g.

Yes, but it changes the meaning slightly.

• Bisogna spegnere la luce = You have to turn off the light
  
  • often understood as the light in the room/house in a general everyday way
• Bisogna spegnere le luci = You have to turn off the lights
  
  • clearly plural, meaning multiple lights

Both are correct. The singular version is very common in Italian for this everyday action.