La luz del fondo de la sala está encendida.

Del is the contraction of de + el (of + the) before a masculine singular noun.

• de + el fondo → del fondo
• Literally: "the light of the back (part)"
  So la luz del fondo = “the light at the back” or “the light in the back (area)”.

Both are possible, but they mean slightly different things:

• del fondo de la sala: literally “of the back of the room”, focusing on which light it is (the one that belongs to / is located in the back area).

  • la luz del fondo de la sala = the light (that is) at the back of the room.

• al fondo de la sala: means “at the back of the room” and usually describes where something is, not which one.

  • La luz está al fondo de la sala = The light is at the back of the room.

In your sentence, del is used because it’s identifying which light (the one from the back), not just giving a location.

Spanish uses ser vs estar to distinguish:

• estar + participle/adjective: temporary state or condition

  • La luz está encendida = The light is on (right now).

• ser + participle here would sound like a passive voice or an unusual description:

  • La luz es encendida would suggest “the light is (usually) turned on (by someone)” and sounds unnatural in everyday speech.

To say the light is currently on, you must use estar: está encendida.

Encendida is originally the past participle of encender (to switch on / to light), but in está encendida it functions as an adjective describing the state of the light:

• Masculine: encendido (e.g. el ordenador está encendido)
• Feminine: encendida (e.g. la luz está encendida)
• Plural: encendidos / encendidas

So está encendida = is on / is lit (adjectival, not “is being turned on”).

Adjectives in Spanish must agree in gender and number with the noun:

• luz is feminine singular: la luz
• So the adjective must also be feminine singular: encendida

Examples:

• la luz está encendida (feminine singular)
• el televisor está encendido (masculine singular)
• las luces están encendidas (feminine plural)

No, that sounds wrong in everyday Spanish.

To talk about the light being on now, you need estar:

• ✅ La luz del fondo de la sala está encendida.
• ❌ … es encendida.

Ser encendido might appear in technical or very specific passive constructions but is not used for this normal “on/off” meaning.

Fondo literally means “bottom / back / depth”. In spatial contexts like this:

• el fondo de la sala = the back of the room (the part farthest from the entrance or from where you are)

So la luz del fondo de la sala = the light at the back of the room.

The pattern here is:

• la luz del fondo de la sala

This is a chain of possessive/locative de phrases:

• la luz (the light)
• del fondo (of the back area)
• de la sala (of the room)

So it’s basically: “the light of the back (part) of the room”.

If you said en la sala, you would be giving the location of the light (“in the room”), not specifying which light belongs to which part of the room. You could say:

• La luz en la sala está encendida.
  = The light in the room is on.

But that has a different nuance: a light located in the room, not specifically the back light of that room.

That word order is unnatural in Spanish.

You want the identifying phrase (del fondo de la sala) right next to la luz, not separated by the verb:

• ✅ La luz del fondo de la sala está encendida.
• ❌ La luz está encendida del fondo de la sala.

In Spanish, descriptive/identifying phrases usually stay close to the noun they describe.

Yes, you can if the context already makes it clear which place you’re talking about.

• La luz del fondo está encendida.
  = The back light is on.

Adding de la sala just specifies which room, useful if there are several rooms or if you’re being extra clear.

In Spanish, you normally use a definite article (el / la / los / las) when you talk about a specific thing:

• la luz del fondo = the back light (a particular light you both know about)

Omitting the article would sound incomplete here. Spanish uses articles more often than English does. English often allows “light is on”; Spanish prefers “la luz está encendida”.

In Spain:

• sala: usually living room or large room / hall (e.g. sala de conciertos, sala de espera).
• habitación / cuarto: more like bedroom or room in a house in general.

So la sala here suggests something like the living room or a larger room, not necessarily a bedroom.

In Spain, the usual word is encendido / encendida with estar:

• La luz está encendida.

In many parts of Latin America, prendido / prendida is also common:

• La luz está prendida.

Both are understood almost everywhere, but in Spain encendida is the more typical choice.

• está (with accent) = 3rd person singular of estar: he/she/it is, you (usted) are

  • La luz está encendida. = The light is on.

• esta (no accent) = demonstrative adjective/pronoun: this (feminine)

  • esta luz = this light

So the accent distinguishes “is” (está) from “this” (esta).