The security industry has historically suffered from a lack of any accepted standards for the measurement of illumination distances. Methods for measuring achievable distances have typically been left to the subjective interpretation of manufacturers without any scientific basis – resulting in varying claims, writes the CCTV lighting product company Raytec.
It is not uncommon to have two illuminators with a similar light output, that are quoted with wildly different maximum distances – because each manufacturer has an opinion on what is classed as an acceptable image quality at their maximum distances. The first problem is that most manufacturers don’t provide calculation data to support their distance claims.
Consider two infra-red images below produced by two illuminators (subject at 70m). Both could claim to deliver 70m-plus performance, but one outperforms the other. Without calculation data, we don’t know much light each illuminator is actually delivering at its maximum distance. And crucially, where does the acceptable benchmark lie?
The second problem is that most manufacturers also don’t tell you the camera specification used to achieve their results. This is especially important if you are comparing one illuminator against another that promises almost identical image quality at a similar distance. How do you know that both illuminators are truly equal? In reality, one illuminator may have actually been tested with a much higher performance camera – which in effect boosts its capability. Beware – this is often how a lower performing or smaller illuminator can ‘appear’ to outperform a higher performing illuminator!
Remember: A manufacturer with a better claimed distance may have used or accepted:
•a much more expensive and sensitive camera
•a much more expensive and higher performing lens
•a more highly reflective surface
•a much noisier picture to “quantify” the published distance.
This has always made it virtually impossible for consultants, installers and end-users to specify surveillance lighting with confidence, reliably compare products and achieve a consistent level of performance.
Many factors which affect lighting performance – but we will focus on achievable distance as the key factor – since this is the headline statement with which most manufacturers lead. Maximum distance should be calculated based on achieving a consistent level of lighting power on scene, so that you can achieve the same quality of image, every time.
But what lighting levels should you adhere to? As we know, there has previously been no standard for this. But, based on decades of practical industry experience, Raytec have launched the industry’s first standard for surveillance lighting called “POWERS” which tackles this issue. With POWERS we’re proud to tell you what WE recommend as an industry benchmark and how you can use this to calculate how far your illuminator will truly shine.
POWERS
When looking at an illuminator, customers ultimately want to know: how far and how wide does it shine, is it efficient and reliable, what features does it have and what level of warranty, certification and technical support will the manufacturer provide? The Raytec “POWERS” standard answers these questions by looking at the following areas:
PPeak Power
OOverall Power
WWidth/Angle
EEnvironmental
RReliability
SSpecification/Features
Surveillance lighting standardisation is a highly detailed and very topical subject. However, this article only focuses on the ‘P’ of POWERS which proposes a scientific approach to calculating distances – arguably the most important area of the standard.
Calculations
Raytec recommend a minimum power on scene of 0.35 μW/cm2 (microwatts per square centimetre) for Infra-Red and 3 lux for White-Light. We calculate all of our illumination distances to these light levels using a medium performance camera (1/3 inch chip) – but you could in theory exceed our distances using a higher performing camera. Working to our recommended light levels with a medium performance camera, you will be able to achieve high quality, consistent images every time and to comply with the POWERS standard.
To scientifically calculate the max distance of your illuminator, you first need to measure the illuminator’s peak power. Peak Power is measured at the centre point of the beam using a light or power meter. At Raytec, we measure this at 3 metres from the light source. Once you have the peak power, you can then apply the inverse square law (a law at the heart of scientific lighting calculations!) – and this will give you the TRUE useable distance of your illuminator.
Example calculation
Maximum Target Distance of Raytec VARIO2 i16 10 degree IR illuminator to deliver target power of 0.35μW/cm2.
Measured Data:
Peak Power @ 3m (Measured Distance) = 10,175μW/cm2 (Measured Power)
Calculation:
(Measured Distance/ Target Distance td)2 x Measured Power = Target Power
(3/td)2 x10,175 = 0.35
td = √ ((9*10175)/0.35)
Target distance = 511.51
Therefore, Raytec quote a max distance of 500m (1,640ft) for the VARIO2 i16 illuminator. We always slightly under-specify our distances so you KNOW you’ll always achieve the distances that we quote on our datasheets. Take care – you may need to apply more light to support higher megapixel cameras or if you are zooming in over long distances.
Raytec can provide testing of third party products in accordance with the POWERS standard, so where there is no published information available, Raytec will measure the product and provide the relevant information. Visit www.rayteccctv.com.
