According to Noise Pollution (Regulation and Control) Rules, 2000, the night…

Concept

The Noise Pollution (Regulation and Control) Rules, 2000 fix ambient noise limits (in dB(A) Leq) by area category, with a separate, stricter limit at night. Hospitals, educational institutions, courts and religious places lie in a Silence Zone (Category D) — the area not less than 100 metres around such places — which carries the lowest permitted limits. Night time runs from 10:00 p.m. to 6:00 a.m.

Application

An educational institution falls inside the Silence Zone. The prescribed Silence Zone limits are:

• Day time (6:00 a.m. – 10:00 p.m.): 50 dB(A) Leq

• Night time (10:00 p.m. – 6:00 a.m.): 40 dB(A) Leq

So the night time standard for an educational institution is 40 dB(A).

Cross-check

The other figures belong to different zones or the day slot: 45 dB(A) is the night limit for a Residential zone, 50 dB(A) is the day limit for the Silence Zone (and the night limit for Residential is 45, not 50), and 55 dB(A) is the night limit for a Commercial zone. None of these is the Silence Zone night limit, which is the lowest of all — 40 dB(A).