Kakabukas ko lang ng ilaw sa kusina.

In this kaka- construction, the doer is commonly marked with the genitive pronoun set, so ko is used instead of ako. That is why kakabukas ko means I just opened/turned on.

Compare:

• Nagbukas ako ng ilaw. = I turned on/opened a light.
• Binuksan ko ang ilaw. = I turned on/opened the light.
• Kakabukas ko lang ng ilaw. = I just turned on a light/the light.

Lang means just, only, or merely. Here it strengthens the idea that the action happened just now. So kakabukas ko lang is basically I just turned it on.

It also follows normal clitic placement, which is why you get ko lang, not usually lang ko in this sentence.

Here, ng marks the thing affected by the action: the light is what was turned on. Filipino changes the marker pattern depending on the verb form being used.

So you can compare:

• Binuksan ko ang ilaw.
• Nagbukas ako ng ilaw.
• Kakabukas ko lang ng ilaw.

All are possible, but they use different grammatical patterns.

Literally, yes, the root bukas means open. But in everyday Filipino, it is also commonly used for switching something on. So magbukas ng ilaw or kakabukas ng ilaw is a normal colloquial way to say turn on the light.

Another common verb for lights is sindi:

• Kakasindi ko lang ng ilaw. = I just turned on the light.

Sa kusina means in the kitchen. The marker sa is used for locations. In this sentence, it tells you where the light is, or where the action is relevant.

In natural English, this is usually understood as the light in the kitchen.

Filipino does not have articles that match English a and the exactly. So ng ilaw can mean a light, the light, or sometimes some light, depending on context.

In this sentence, English will usually say the light, because it probably refers to a specific light in the kitchen.

Yes:

• kakabukas = just opened / just turned on
• ko = I / my / me, here marking the doer
• lang = just / only
• ng = object marker
• ilaw = light
• sa kusina = in the kitchen

So the whole sentence means: I just turned on the light in the kitchen.

Yes. Some common alternatives are:

• Binuksan ko lang ang ilaw sa kusina.
• Nagbukas ako ng ilaw sa kusina.
• Kakasindi ko lang ng ilaw sa kusina.

The original sentence is especially good for emphasizing that the action happened very recently.