PIR Technology In Interior Lighting – The Basics

05 July 2018

Nowadays, most people often want to source PIR activated LED interior lighting or LED sensors to integrate it into an existing circuit when buying from Dun-Bri. This article aims to give you a greater understanding of what PIR means, and what it actually is…

So, what does PIR stand for?
PIR stands for Passive Infra-Red.

And what does ‘Passive Infra-red’ mean?
Passive in this context refers to the fact that the sensor neither generates nor radiates energy to detect infra-red. Infra-red means ‘below red’ – infra-red light waves have less energy than red light waves. Infra-red is just outside the spectrum of light visible to the human eye.


Visible light spectrum


Everything with a temperature above absolute zero (-273°C) emits infra-red heat radiation.

How does it work?
A Passive Infra-Red sensor sees infra-red heat and reacts to the movement of that heat. When a PIR sensor sees movement of heat an electrical signal is generated, it is the size of this signal which will cause the PIR circuit to react (or not react) and switch on a light. The bigger the signal generated then the more chance the circuit will react and switch on.

The amplitude of the signal is affected by 4 things:

  1. Difference in ambient temperature and target temperature – the bigger the difference, the bigger the signal.
  2. Size of target – the bigger the target, the bigger the signal.
  3. The speed of movement – the faster the speed, the bigger the signal.
  4. Proximity of target to the sensor – the closer the target/movement is to the sensor, the bigger the signal.

Then what’s the difference between an SMT and a CAN PIR sensor?
SMT (Surface Mount Technology) sensors are smaller and more discreet making them an attractive solution when designing low-profile lighting. The downside is there are not many options on the market, they only contain the sensor elements, and they can be more prone to false triggering. Surface Mount Technology, or its acronym SMT, can be found across thousands of products and product types from LED emitters themselves to resistors and other electrical components.

CAN PIR sensors utilise an industry standard can as a package and are a lot larger by comparison to an SMT sensor. There are a lot more options and manufacturers on the market. The can package will often contain key components associated with the control circuit and this makes them inherently more immune to false triggering from electrical noise.

Where can I get more help and advice?
As usual, you can contact us for more help and advice either prior to purchase, or afterwards – call us on 01763 274185 or email sales@dun-bri.com…


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