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.

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.

Comparing Sources of Light