The IR range on a spec sheet, and the range on site
The IR (infrared) range listed in a spec sheet is measured in clean air, in a fully dark room — a condition that rarely exists on a real site. Rain, fog, airborne dust and a white wall near the lens all cut it down, because infrared light, just like visible light, loses strength passing through particles or bouncing off a nearby bright surface straight back into the sensor.
An example of the drop-off
As an illustration: a camera rated for 30 m of IR range in clean air can, in heavy rain or thick fog, drop to half that range or less in practice — it isn't unusual for 30 m to become 10 to 15 m in poor conditions. That isn't a faulty camera, it's the physics of infrared light in moisture and airborne particles.
That gap is why range for a perimeter or an entrance shouldn't be chosen off the highest number on a spec sheet, but with margin built in.
WDR: when a strong light behind the subject creates a silhouette
When a strong light source — a streetlight, headlights, sunrise — sits behind someone walking through the frame, a camera without WDR (Wide Dynamic Range) exposes for the background and turns the face into a dark silhouette. WDR processes the bright and dark parts of the frame separately and keeps the face visible in front of the bright source.
At an entrance, where the job is identification, WDR matters more for the final result than extra megapixels on the same camera.
Colour against a grey shape: use the light that's already there
Where street or facade lighting already exists, use it instead of relying only on the camera's built-in infrared diode. A camera working in that existing light captures colour, and colour describes clothing, a vehicle and objects in a way a grey infrared frame can't.
Infrared stays necessary wherever there's no light at all, but it only gives you a grey shape — enough for detection, often not enough to describe what was recorded.
Recommendation
For positions where the job is identification — an entrance, a till, a gate — choose WDR and, where possible, existing lighting before choosing off the highest IR range figure in a catalogue. Real conditions (rain, fog, nearby walls, light sources in the frame) get checked on site, because a spec sheet on its own doesn't answer what will actually be visible at 11pm in November.