Lallo, the 25-year-old man, presented with h/o of pain, redness & watering of left eye for last 1 day. There is also intolerance to light. Most probable diagnosis is –
First see the information in question :

Pain, redness & watering (lacrimation)
Intolerance to light (Photophobia)


Acute posterior uveitis does not cause pain, redness, photophobia and lacrimation. The most prominent symptom is diminished vision especially if the lesion involves macula, maculopapillary bundle and optic nerve.
In Epidemic keratoconjunctivitis, initially there are symptoms of conjunctivitis, i.e. conjunctival congestion, lacrimation, chemosis, lid hemorrhage and conjunctival hemorrhage. Conical involvement (Photophobia) occurs at around one week after onset of conjunctivitis. In this question, all the symptoms are appearing at same time (since one day).
Now we are left with keratitis (corneal ulcer) and acute anterior uveitis. Both can present with pain, redness, lacrimation and photophobia. We cannot differentiate between these two on the basis of information provided in the question.
But, we have to choose one option, and keratitis seems to be best because :-


The more classical signs of anterior uveitis, i.e. KPs and aqueous flare have not been mentioned in the question.
Photophobia is more prominent in conical involvement.
Keratitis
Acute anterior uveitis
Acute posterior uveitis
Epidemic kerato conjunctivitis