I came across the use of the word luí today to mean bed, instead of Leaba. I wondered whether this is simply an alternate word, or a dialect thing?

leaba "bed"

luí "lying down".

Tá sé sa leaba. "He is in bed."

Tá sé ina luí. "He is lying down."

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Múinteoir Gaeilge - Irish Teacher
My "specialty" is Connemara Irish, particularly Cois Fhairrge dialect, but I can also speak Ulster and Munster Irish with native-level pronunciation.
Is fearr Gaeilge ḃriste ná Béarla cliste, cinnte, aċ i ḃfad níos fearr aríst í Gaeilge ḃinn ḃeo na nGaeltaċtaí.
Gaeilge Chonnacht (GC), go háraid Gaeilge Chois Fhairrge (GCF), Gaeilic Uladh (GU), Gaelainn na Mumhan (GM), agus Gaeilge an Chaighdeáin Oifigiúil (CO).

Yep. Though I can see where one might assume that "luí" could mean "bed," as you'll hear "ina luí" used with the same sense as "sleeping" or "in bed."

Redwolf

Oh, of course! I remember now GRMA!

You'll find the same thing with "suí." While "Tá mé i mo shuí" literally means "I am sitting," it's also used to mean "I am awake" (as in "I'm sitting up while everyone else is lying in bed fast asleep").

Redwolf

Yeah, it more or less means "risen":

Tá an ghrian ina suí. – The sun is risen.

And tá an ghrian ina luí - "The sun has set."

_________________
Múinteoir Gaeilge - Irish Teacher
My "specialty" is Connemara Irish, particularly Cois Fhairrge dialect, but I can also speak Ulster and Munster Irish with native-level pronunciation.
Is fearr Gaeilge ḃriste ná Béarla cliste, cinnte, aċ i ḃfad níos fearr aríst í Gaeilge ḃinn ḃeo na nGaeltaċtaí.
Gaeilge Chonnacht (GC), go háraid Gaeilge Chois Fhairrge (GCF), Gaeilic Uladh (GU), Gaelainn na Mumhan (GM), agus Gaeilge an Chaighdeáin Oifigiúil (CO).

Also: luí na gréine – sunset

Makes sense!

In what sense did you come across this phrase?