What does IRE mean when quoted with Lux light levels for CCTV cameras?
We’ve noticed that many people seem to be a little baffled by this mysterious occasional mention of the term IRE, so we thought we’d just write a quick article to explain it in lay terms for you.
There is a good technical explanation over on Wikipedia, but as often happens it is a bit too technical if you are starting from the point of having no idea!
IRE stands for Institute of Radio Engineers, but that’s not important, you want to know what it means.
Well, keeping this within terms easily understood by lay-men:
The squiggly line above represents a composite video signal.
We refer to a good signal as being 1 volt peak-to-peak.
The Institute of Radio Engineers came up with the term IRE to represent the composite video signal in percentage terms i.e. 100IRE equals 100%, a full (good) signal.
Now the buyer beware bit. Just about the only time you see IRE quoted is when a manufacturer is trying to apply specmanship i.e. they are claiming that their camera can ‘see’ in very low light levels, but in fact it only does so poorly, and produces a less than good composite video signal.
For example 0.05 Lux (30IRE) means that in light levels measured at 0.05 Lux the camera will produce an image, but it’ll be a poor one, with a composite video signal level at only about 30% of what it should be. Effectively this would be a fairly useless image, and perhaps the camera is only really useful down to a higher lux level of say 0.5 Lux …
Of course, due to our human tendency to ignore the bits we don’t understand, it makes for quite clever marketing really; most folk just read the specification, see the incredible ‘see-in-the-dark’ capability indicated by the very low lux light level claimed in the specification and proceed to buy the camera.
To gain a better understanding of relative lux light levels take a look at our free chart.