Can someone explain to me how a light beacon managed to be seen by ships, hundreds, if not thousands of light years away? and was somehow as bright as a star.
I believe it was established that the beacon was transmitting on subspace bands as well. See the quote below, emphasis mine.
SARU (ON COMMS): Captain to the bridge.
SARU: Massive photonic activity on the Klingon object, Captain. Output is over one billion lumens per square meter.
CONNOR: Optical sensors overloading.
GEORGIOU: Bring plasmatic filters on line.
CONNOR: Rerouting power.
GEORGIOU: Is that a weapon? It seems to be some sort of signal emitter. Where are my filters?
CONNOR: They're at 100%, Captain.
(HIGH-PITCHED SOUND GROWING LOUDER) (HIGH-PITCHED RINGING) - (HIGH-PITCHED RINGING CONTINUES)
CONNOR: Initiating emergency shutdown. That noise is some kind of electromagnetic subspace wave-form. Narrowing channel range. Adjusting orientation to minimize dispersal.
GEORGIOU: Somebody turn it down.
CONNOR: Aye, Captain.
GEORGIOU: All the way down.
SARU: Acoustics are muted. That's the ship's superstructure in sympathetic vibration. It's a signal pulse.
GEORGIOU: Is there a message?
BURNHAM: This may be the message. Captain, what if they're calling for the same thing we are? Backup.
GEORGIOU: Long-range sensors to the maximum, Saru. If more Klingons are on their way, I want as much notice as possible.
There would be no need for long-range sensors if that signal were simply a light signal...