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Sources of Light

Light Emitting Diodes (LEDs) are semi-conductors that naturally emit a narrow band of light, are highly reliable and very small, making them suitable for a number of lighting applications. LEDs are the fastest growing lighting solution in the world and are now used for everything from lighting for surveillance, lighting for vehicles, domestic lighting and now, even for street lighting.

Since the 1960s the performance of LEDs has increased significantly with developments in LED technology, optics and materials science allowing lighting output to be doubled approximately every 36 months.

Advantages

Efficacy: Greater output of light per watt than most technologies.

Long Life: LEDs have a useful life of over 44,000 hours (10 years continuous night-time use) with time to complete failure even
longer.

Slow Failure: LEDs will degrade slowly over time rather than experience the catastrophic failure of a typical bulb.

Start up time: LEDs can reach full brightness in 10-20 nanoseconds and can re-start just as quickly.

Pulsing: An LED can be powered on/off multiple times per second for prolonged periods without damaging product life.

Power adjust: LEDs power can be both dimmed or boosted to react to different on scene requirements very easily.

Resistant to Vibration: As LEDs are solid state devices, and have no fragile filament, they are durable and resistant to vibration either from wind, transport or re-location.

Highly Directional: With the use of small optics LEDs can provide a precise and highly directional beam pattern. Bulb based illuminators often require large reflectors to focus the light beam and even then it is difficult to control the direction of the beam efficiently.

Size: LEDs are small and can lead to much smaller and neater illuminators.

Precise Wavelengths: LEDs are developed to emit an exact wavelength or colour of light without the need for additional filters which means LEDs can deliver light more efficiently, run at lower operating temperatures all at a more cost effective price.

Disadvantages

Purchase Price: LEDs have a higher initial purchase price than old technology lighting. However long life-times together with energy, maintenance and CO2 savings mean that LEDs can be a cost effective solution in the medium to long term.

Efficacy Droop: As current is increased through an LED the efficacy of the unit decreases. However, this can also be an advantage of LEDs – making it possible to maximise light output at the expense of efficacy or vice-versa depending on the specific
needs of an installation.

Temperature Sensitivity: Both LED performance and lifetime depend on both the ambient temperature and the thermal control of the illuminator. Overheating an LED dramatically reduces operational life.

LEDs advantages versus traditional technologies vary depending on the other technology in the comparison.

LED lighting vs other technology lighting

In this test a fence line and an area up to 5m inside the fence line needed to be illuminated using existing lighting columns. The LED solution produced a better colour representation, a better quality of light for the CCTV camera and lowered electrical consumption and maintenance costs. Importantly, the image illuminated by LED lighting shows that the fence line is inside an external wall, the image illuminated by sodium lighting makes the wall and fence look indistinguishable.

In this recent installation a power station was using High Pressure Sodium lighting to illuminate a work area. Switching to an LED solution produced a much better image and better colour rendition. Importantly the colour of all the machinery, switches and dials is much clearer under LED lighting.

Comparing Sources of Light

Incandescent Lamps (including Halogen)

Bulb life is limited and they are highly inefficient making them expensive to run (typically500W) and to maintain (up to 3 bulb changes per year). End users are increasingly moving away from using halogen based lighting products in favour of longer life LEDs and many governments are taking steps to ban incandescent
lighting.

Incandescent bulbs were the first bulbs developed and are highly inefficient, wasting 90% of their input energy as heat. Their heat output is such that they are extremely hot to touch and can heat surrounding objects in close proximity.
Halogen bulbs provide a minimal increase in efficiency but still waste as much as 85% of their input energy as heat. Halogen bulbs are smaller and higher pressure than incandescent bulbs causing them to have extremely hot surfaces hazardous to the touch. Bringing the bulb into contact with cold surfaces such as residue from fingerprints, particularly sodium, may cause bulb failure.

HID Lamps

HID lamps can be used for CCTV and general area lighting. They are efficient, provide good colour rendition (expect low pressure sodium), and are long life – typically up to 12,000 hours. However, they suffer from a slow start (up to 5 minutes) and cannot be turned on immediately after being turned off.

High Intensity Discharge (HID) lamps are 60-80% efficient and compared to incandescent and fluorescent lamps provide much more light from a smaller package. HID forms include low pressure sodium (unsuitable for CCTV due to its yellow colour output), high pressure sodium(more acceptable but produces worse colour rendition than Metal Halide) and Metal Halide. Metal Halide HID bulbs provide a very natural, cool clear White-Light with excellent colour discrimination. However, they still cannot match the quick start or long life of LEDs. HID lamps are commonly used for street lighting and in car headlights.

LEDs

LEDs are the fastest growing lighting solution on the planet. They are extremely efficient and offer unbeatable reliability. LEDs
offer the lowest running costs (less than 100 watts for the largest units) with the longest operating life and lowest maintenance factor.
Light Emitting Diodes (LEDs) are semiconductors that naturally emit a narrow band of light. They are a relatively new development in lighting but their usage is expanding rapidly on the back of their clear technical advantages. LEDs are comparatively expensive to purchase but provide extremely long life up to 100,000 hours. In comparison fluorescent bulbs typically last 10,000 hours and incandescent bulbs 1,000.

LED efficiency is typically 80-90%. The advantages of LEDs are multiple and are listed on page 2 in detail. They include extremely low electrical consumption, low operating temperatures and continuity of colour throughout the operating life of the LED. Unlike traditional bulbs LEDs are also highly durable, resistant to vibration and their hard casing makes them difficult to break. They are quick start devices and are also capable of emitting light at a given wavelength without the need of a filter.

Comparing different LED technologies

Low power LEDs are typically of the through-hole variety. They tend to be very basic and generate small amounts of light with limited heat management. High power LEDs are typically surface mount technology (SMT) which gives the LED itself a large flat surface area to be mounted to the PCB. This makes it easier for the LED mounting system to be mechanized, allowing a precise and uniform mounting pattern and also provides a larger surface area to dissipate heat. With the larger surface area SMT LEDs can be driven harder without compromising performance.

High power LEDs generate far more light and far more heat than low power LEDs so thermal management of these LEDs is crucial. Without adequate thermal management and heat sinking high power LEDs will fail quickly. Multi-Chip LEDs are designed for applications where size is critical. These LEDs concentrate a number of individual LEDs (either low or high power) into a small area. They can also focus the light to allow the beam pattern to be more tightly controlled. However, multi-chip LEDs, because of their close proximity, generate large amounts of heat which make thermal management and life control difficult. Multi-chip LEDs can compromise on lifetime to produce light from an extremely small package.

In the same way that most camera manufacturers do not manufacture their own CCD or CMOS chips, typically illuminator manufacturers do not develop their own LED chips, they use LEDs manufactured by specialist LED chip manufacturers. This means that power management, thermal management and optics are the most important factors to ensure LEDs deliver on their expected performance and achieve the lifetime and light levels that they are capable of. Not only are all LEDs different, but the same LED in different hands delivers very different results.

Pro-Tip: For surveillance lighting or lighting for safety critical environments, where the size of the illuminator is not restricted, it is better to use a quantity of High Power LEDs to provide a product with the best light output and life expectancy rather than using a multi-chip LED package or the less powerful LED chips.

Pro-Tip: Two lighting manufacturers can use the same LED in their illuminators but achieve significantly different light output and reliability depending on the quality of their thermal management, heat sinking and optical system developed around the LEDs – as well as internal quality control procedures.

Choosing which Wavelength of Light

White-Light

• White light is a mixture of visible wavelengths from approximately 400nm to 700nm.
• It covers all the colours of the visible spectrum from red, orange, yellow, green, blue, indigo and violet.
• The human eye is at its most sensitive at around 555nm, in the green range of the visible spectrum.
• White-Light provides the opportunity to illuminate an area for multiple uses: Pedestrians; CCTV; staff or vehicles.
• White-Light can be used as a visual deterrent – activated when an intruder enters a secure area.

Infra-Red

• 715-730nm is overt, visible Infra-Red. It produces a red glow like a traffic light. It is not widely used for LED illuminators and tends to be a legacy option from old fashioned Halogen style illuminators.
• 815-80nm is semi-covert Infra-Red. It produces a very faint red glow only just visible to the human eye. Most IR sensitive cameras are fully capable of seeing 815-850nm.
• 940-950nm is covert IR, virtually invisible to the human eye. However the sensitivity performance of all CCTV cameras drops significantly with 940nm, by as much as 50% – with achievable distances dropping accordingly. CCTV lenses are also less efficient with 940nm light.
• Because Infra-Red illuminators produce light at one given wavelength and White-Light illuminators need to deliver a range of colours to product White-Light, IR illuminators can cover longer distances.
• Infra-Red illuminators can be used to provide semi-covert or covert illumination without creating any light for an intruder or any light pollution.
• Infra-Red light can only be viewed with a camera system.

The best solution for most Infra-Red applications is 850nm. It is both more discreet and more powerful than illuminators using 715-730nm LEDs and achieves much greater distances than 940-950nm illuminators as camera sensitivity seriously inhibits performance with 940-950nm illuminators. Focussing is also more difficult at 940-950nm and ‘focus shift’ between day and night images is more likely to occur.

Pro-Tip: An 850nm illuminator can produce less radiant flux (power) than a 940nm illuminator but still achieve significantly further distances because cameras tend to be around 50% less sensitive to 940nm Infra-Red.

Measuring White-Light

The advantage with White-light is that it is visible to the human eye so beam patterns and distances can be
easily evaluated – unlike Infra-Red light. There are two important measurements for White-Light illuminators:

1) Lumens are used to measure the total amount of visible light emitted by an illuminator (luminous flux).
2) Lux measures the amount of luminous flux (number of lumens) falling over a given area. It is a measure of illuminance to measure the intensity of light on a surface. 1 lux is equal to one lumen per square metre.

The Lux level at any given point depends on a number of factors including output angle, installation height, mounting angle and distance from the illuminator. In North America the foot candle is still widely used as a unit of measurement. 1 Lux is approximately equal to 10 foot candles (10.764 to be precise).

Pro-Tip: Manufacturers should use the total number of lumens (luminous flux) on datasheets as an absolute measure of White-Light power output. Because Lux levels are dependent on a number of installation factors they cannot be specified at product
level – only measured as part of the installation and commissioning process. It is the quantity and the distribution of the light that together govern the quality of the illumination.

The White-Light Measurement Process

Every White-Light illuminator should have independent photometric testing to confirm performance. Without independent test data there is no credibility to the distance or performance claims of a White-Light illuminator. The photometric testing measures the illuminator in a spherical chamber to capture all the light emitted by a source and then testing is done to plot illumination output at different angles.

1: Independent photometric testing delivers precise data on each illuminator which can be loaded into a lighting design software package

Measuring IR

Assessing the performance of Infra-Red illuminators is much more difficult than assessing the performance of White-Light because a lighting design cannot be evaluated with the human eye; it must be viewed through a camera and lens and the performance of the camera and lens affects the way the IR performance is perceived. However, the specification and measurement of IR can be done in exactly the same way as a White-Light illuminator, it just requires a different sensor to measure the IR.
Traditionally IR illuminators have been measured in terms of the distance they can illuminate. However, this system fails to measure the true performance of an illuminator before the impact of the camera and lens, and is highly subjective and open to manipulation and misrepresentation. Consider an IR illuminator such as the RM100-AI-30. If we quote the distance of this illuminator as 100m what does it mean? First we must understand the relationship that the lens and the camera sensor have on our perceived performance of the light.

The Effect of Sensor Size

The light collected by individual pixels of a camera is proportional to the size of the pixel. So with a 3MP camera with a resolution of 2048 x 1536 pixels, the size of those individual pixels will be larger on a ½” camera than on a ¼” camera, they will each capture more of the available light so the ½” camera will require less light to power an image. Below is a table showing the relative size of
different camera sensors.

The Effect of the camera lens

The f number of a lens is a mechanical ratio and describes the amount of light passed through the lens to the camera sensor. Essentially the smaller the f number the more light passed to the camera sensor. Below is a table showing the light passed through the lens by f-stop rating using an F1 lens as the base number.

Pro-Tip: A simple calculation to determine how the F-Stop rating affects the light capable of passing through a lens can be written as 1 over the f-stop² (for example an F2.0 lens passes 25% of the light because 1 divided by (2²=4) = 0.25. The transmission characteristics of a lens will further impact the amount of light transmitted.

Light and Eye Safety

As we cannot see Infra-Red our eyes cannot automatically adjust to protect from overexposure. However, Infra-Red does produce heat – it is the Infra-Red we can feel on a hot sunny day as warmth. It is this heat from Infra-Red that we can use as an indication of safety. The general rule of thumb is that if you can feel the heat of the IR unit then do not look directly at the source.
Even the most powerful IR units, at angles of 10 degrees, are fully eye safe beyond distances of 2m. Raytec take eye safety very seriously. All Raytec IR products including RAYMAX, PLATINUM and FUSION illuminators have been tested and classified as Class
1M laser devices. A Class 1M laser device is safe for all conditions of use with the naked eye. Class 1M lasers produce large-diameter beam patterns, or beams that are divergent. The MPE (maximum exposure time) for a Class 1M laser cannot normally be exceeded when viewed with the naked eye.

Evaluating Running and Maintenance Costs

When you switch to low energy LED illuminators delivering low running costs and long life, an organisation such as a hospital, using 100 CCTV and security lights could be saving £46,000 per year, and these savings are only set to increase as energy costs increase!

Environmental and energy consumption issues are high on the global agenda. Given that £1 from every £5 spent globally is use don lighting, and much of this spend is on inefficient or unnecessary lighting particular attention should be given to this area. The pressure to save energy by looking at running costs, maintenance costs and an organisation’s carbon footprint will only increase as energy costs increase. Both public and private sector users are looking for methods to reduce costs an minimize their energy requirements and lighting should be one of the first points on the agenda.

Traditionally lighting has been delivered by mains powered lamps and although some lamps are more efficient than other the future of light lies with Light Emitting Diodes (LEDs). Low energy LED illuminators deliver lower power consumption, lower running costs, zero maintenance and provide longer life compared to older style lighting which can also be extremely slow to start up.
LED illuminators are a highly efficient light source which can deliver huge savings to end users.

Why switch to LED lighting:

• Potential saving on 1 illuminator of £460 ($736) per year
• Over ten years this is a potential saving of £4,600 ($7,360) for 1 illuminator
• Potential saving on 100 illuminators of £46,000 ($73,600) per year
• Over ten years this is a potential saving of £460,000 ($736,000) for 100 illuminators
• Labour saving of 2 bulb changes per year – on every illuminator.
• Over 10 years this is a saving of 2,400 bulb changes for 100 illuminators
• LEDs provide increased security (because they don’t fail leaving a site unsecured while waiting for replacement parts)
• Potential saving of 667Kg CO2 on 1 illuminator, each year.

Pro-Tip: Raytec provide an interactive “Energy and Cost Saving Calculator” free of charge to help installers and end users calculate the possible savings in switching to LED technology. Visit www.rayteccctv.com to download.

LED Lifetime – Comparing Specifications

An LED is only a long life device if it is harnessed, powered and controlled correctly. The worry for end users is that many manufacturers simply do not know the true reliability and lifetime of their LED illuminators. It isn’t simply a case of using premium LEDs; it is the power management, heat management and optical management of those LEDs that affect product life and performance. Badly designed LED illuminators subscribe to the mantra of “live fast, die young”. LED illuminators often have no serviceable parts so a failed product means more than a simple repair, it means a whole new unit. Not only are all LEDs not made equal, but the same LED is not equal in different hands.

To understand the lifetime of an LED it is important to consider the meaning of ‘lifetime’ in this context. Is it when the product no longer produces any light, or when the product no longer produces ‘enough light’ (sometimes defined as useful life)? For an individual LED, lifetime is considered to be the point when the LED power output falls to lower than 70% of its original value. We can use the same 70% figure to measure the output of a full LED illuminator. The US Department of Energy and the Next Generation Lighting Industry Alliance take a harsher stance, recommending lifetime of an illuminator to be “when half of the LEDs in a product have fallen to below 70 percent of their average initial light output for any reason”.

Raytec understand that the lifetime of an LED illuminator depends on a number of factors, the most important of which is thermal management of the LEDs. In general, product lifetime decreases as temperature increases. Raytecs’ industry leading reliability and 5 year warranty package are the result of a number of quality control and quality design measures:

• Our LED technology is field proven.
• Our LEDs are powered from a constant current source to reduce the impact of major temperature increases on the electronics and environmental changes.
• Every illuminator goes through a multi-point testing process prior to despatch.
• Raytec are fully ISO9001 certified to ensure quality throughout the design and manufacturing process.
• We have developed a Cool Running Thermal Management System to effectively remove heat from the LED chips and prolong LED life.

Internal vs External Control Electronics

The lifetime of an individual LED can easily be up to 100,000 hours – the equivalent of almost 23 years of full night-time usage. However, the lifetime of a full LED illuminator is also constrained by the control electronics and here we see a big difference between serviceable and non-servicable illuminators.

Normally low voltage LED illuminators (12-24V ac/dc) have electronics built into the fully sealed LED illuminator which cannot be easily accessed or replaced. High voltage (110-240Vac) LED illuminators tend to have external electronics, often in a separate box (although this separate box can be fitted to the illuminator or remote) and therefore the control electronics can be replaced, repaired and serviced when required. Given that the lifetime of a well designed and thermally managed LED illuminator will be constrained more by the control electronics than by the lifetime of the individual LED chips, this is a major advantage of external PSU systems.

Controlling LED Lifetime – the 2 Schools of Thought

Although they degrade slowly, all LEDs degrade over time. They are no different to ALL electronic components in this regard. Given that LEDs degrade the issue for manufacturers is how we control and limit this degredation. The key to remember here is that LED degredation is primarily linked to operating temperature at the LED chip.

Method 1: Managing Lifetime though Intelligent Product Design

Method 2: Managing Power Output

Some manufacturers take the approach that it is best to keep a consistent light output from the illuminator. As an example, one manufacturer uses LEDs set to 60% of their maximum power (20% below Raytec) and as the LEDs start to degrade (either exact power output is measured or the LED usage can be plotted against degredation in an internal clock) power to the LEDs is increased so they start to operate at above their factory default setting of 60% in order to deliver the same power on scene.

The problem with this technique is that as the LEDs start to degrade, increasing the power and stress through the LEDs will only serve to accelerate their degredation and lead to premature product failure. So it is a question of does the customer want the longest possible life from their illuminator, or do they want a consistent light output with a shorter product life?

Recommendations for Managing LED Life

Raytec believe it is far better to control and manage the LEDs to limit their power loss, to maintain their performance, and to achieve the maximum possible lifetime from an illuminator. However, Raytec have the ability to manage power output if a particularly site requires it (via the Perma-Light function in the Pro Series PSU). In addition Raytec are unique in providing an “Eco-Logic” function which offers significant improvement to product life whilst also delivering significant energy savings.
Selecting the Eco-Logic function allows the illuminator to operate at only 50% of normal power (achieving 71% of normal distance) and switching to full power only an activation via an alarm or external trigger.

What happens if a single LED fails?

Raytec illuminators are designed in a manner which allows a few LEDs to fail without affecting the remainder of the unit. Each product is designed in individual strings of LEDs which are powered independently. For example, a unit containing 100 LEDs may be split into 10 strings of 10 LEDs. If a single LED fails then the other 9 LEDs in that string will each share the power of the 1 lost LED. If 1 string fails then the other 9 strings share the power of the 1 failed string. The result is that the power of the lost LED(s) is borne by the remaining LED(s) so the power output from the illuminator remains unchanged!

The important thing to remember here is that Raytec LEDs are factory set to operate below their maximum tolerance. This means that around 20% of the LEDs can fail and the performance of the unit will remain unchanged without damaging the lifetime of the unit.

Comparing Different Night-Vision Technologies

Active Infra-Red vs Passive Infra-Red (Thermal)

Although these technologies are both designed to provide night-vision in dark environments, they deliver very different results. In many ways they are complementary technologies and can be successfully deployed together in the high security environments. Active Infra-Red illuminators project light onto a scene to allow monochrome (black and white) or day/night cameras to produce a monochrome image. No ambient light is needed as active Infra-Red products generate light that the camera can see but the human eye does not. The results from an Active Infra-Red CCTV scene are similar to what the human eye can see during daytime – but in black and white. Facial details can be seen, lettering and logos can be read on clothing or signs and with Active Infra-Red it is possible to detect, observe, recognise and identify subjects in accordance with the UK Home Office Scientific Development Branch (HOSDB) guidelines. Thermal Imaging relies on producing an image from variances in temperature range throughout the scene.

These systems pick up radiated Infra-Red as heat signatures. The thermal camera then creates an image based on these heat measurements with some “false colours” to identify different ranges of heat. When using thermal imaging, it is sometimes easier to detect a warmer object (a person or animal) against a colder background (the ground or building) because the contrasting temperatures are represented by highly contrasting “false colours” on the monitor. For this reason it can b  easier using thermal imaging to detect “something” in the scene. However, the resolution of thermal imaging systems (typically 160×120, 320×240 and 640×480 pixels versions are available) is considerably lower than conventional video. Thermal imaging cannot see facial details, lettering or logos and can only detect changes in surface temperature within the scene. Thermal imaging systems are also significantly more expensive than traditional CCTV cameras with supporting active Infra- Red.

In practice Active Infra-Red has a far greater range of uses because it produces an image more familiar, more meaningful and containing more data for humans. For particularly high security sites it is not uncommon for Active Infra-Red and Thermal Imaging to be used together. Thermal Imaging is used to quickly detect if an object is in a scene, and then the active IR and CCTV is brought into action to identify the object / person and to evaluate the potential risk.

In the picture below, the person on the left is seen in total darkness using active IR. The person on the right is seen in total darkness using passive IR (thermal imaging)

Pro-Tip: We call Infra-Red illumination ‘active’ because the illuminator itself generates the light the camera needs to see. Thermal Imaging is considered ‘passive’ because it relies simply on picking up information (temperatures) existing on the scene to produce a picture.