We will answer this question on two different levels of complexity, so no matter what your level, you can gain a suitable level of understanding!LEDs – A Basic Definition

An LED is a Light Emitting  Diode. This LED is a form of solid state light bulb with a truly unbeatable lifetime. An LED works by directly converting electrical energy into light photons over a semiconductor junction. There are no problems such as breaking glass or mercury contamination as are associated with most other light sources.

LEDs – Defined a little more!

A  diode  is  a  semiconductor  device  that  only allows electrical current to flow in one direction. In the case of an LED, the diode is manufactured in a special way so that its prime function  is to emit light of a particular wavelength.

Semiconductor diodes are a junction of two materials. One material has a surplus of positive charge holes*, known as the P region. The other has a surplus of negative charge, electrons, known as the N region. Where the two materials meet is referred to as the PN junction. The junction acts as a barrier to the flow of electrons between the P and the N regions. Only when sufficient voltage is applied to the semi- conductor chip, can the current flow, and the electrons cross the junction into the P region. Each time a negative electron recombines with a hole, electric  potential energy is converted into electromagnetic energy. For each recombination of a negative and a positive charge, a quantum of electromagnetic energy is emitted in the form of a photon of light. This semiconductor material is usually a combination of the chemical elements gallium, arsenic and phosphorus.

Applying  an inverse polarity (positive and negative the wrong way round) produces a gap between the electrons and holes (depletion region), which will not allow the electrons to combine with holes, hence no current  will  flow and no light will be emitted.

*the term holes is used to indicate the absence of an electron, the reason for the positive charge.

The colour is created by the LED itself without the use of gels or filters. The chemical composition of the semiconductor materials within the LED define the colour of the light produced and the light emitted is monochromatic (single wavelength). Red, green, blue, amber, and several white colours can be created.

A white LED is actually a blue LED with a special phosphor coating within the LED structure which converts blue light into white light. This is the reason that many LEDs emit a very cold colour of light, typically in the region of 6000ºK.

Warmer white LEDs can now be created using an innovative new phosphor coating technology incorporating  red and white emitting phosphors. Our standard white colours now include  6000K, 4100K, 3000K and 2700K.

This depends on the installation and the products used. Traditional  low power LEDs are provided with a constant voltage then a resistor is used to regulate  the current  to each LED. High  power LEDs require  a more sophisticated  method  to regulate the current to each LED. A typical 1.2W LED requires  a regulated  constant  current  of 350mA, the LED itself  will  self regulate it’s voltage. If a chain of LEDs are used then they must be wired in series, so each LED receives the required 350mA.

The 350mA is provided by specialist  power supplies often referred to as drivers.

Each driver uses different cable types dependant on the type of fitting it is powering, and all can be mounted remotely – distances again vary dependant on the specific type. For further information  on this please see the acdc specification sheets and driver matrix chart.

acdc can also provide a special project solution where each individual  fitting  has it’s own miniature inbuilt  current regulating  driver. In the case of these fittings  the wiring is connected in parallel as with conventional wiring  and the voltage supplied is a constant 24V.

Halogen

Halogen light sources are available in a range of different  sizes and outputs, with a 50 Watt lamp the  most  popular  selection.  Although halogen light sources have a high output, their lifetime is often criticised  as one of the major problems. Colour rendering is good, in line with warm white LEDs at 90 CRI. Other problems include their high operating temperature, which makes them unsuitable for use in possible contact areas, especially in ground and poor efficacies at around 16 lumens per watt.

Fluorescent

Fluorescent lamps have high lumen outputs and good efficacies  at around 55 to 60 lumens per watt. For recessed linear applications fluorescent is an option, but the shadow gaps and hot spots often spoil the lighting  effect. The main difference  is  in  life,  with LEDs lasting  50,000 hours,  compared  to  10 -  15,000 hours  with fluorescent. Colour rendering is again good, greater than 90 CRI, and in line with warm white LEDs. Fluorescent is a glass light  source and therefore also carries a breakage risk.

Fluorescent lamps also contain  mercury, which creates major recycling  issues. Another important difference between fluorescent and LEDs is that the beam from the LED is directional (120 degrees without optics), whereas the output from the fluorescent lamp is omnidirectional with 66% less light  emitted  forward  from the lamp. Comparing outputs is therefore difficult, as LED output is 66% more efficient, lumen comparisons are difficult. The Ciro system is available from acdc offering an excellent even and bright output for recessed coffer lighting.

Fibre optic

Fibre optics use a glass or plastic ‘fibre’ to carry the light from a remote projector housing either a sodium  or halogen light  source. The system is used  to  create  small  twinkles  of  light,  point sources, or sometimes as a linear light  source. The twinkle effect is often used for decorative ceilings etc. and for this they are ideal.

For more powerful points of light, fibre is sometimes used to illuminate  museum pieces as the hot light source is mounted remotely to the light point itself. For linear applications  fibre can be used, but the output is relatively low, with only a dim glow emitted.

Housing the large projectors can often be tricky and matching cable lengths to give an even illumination is part of drawing up a project solution. As the bulk of the fitting  is remote from the light point, small points can be created compared to other light sources, although there is clearly a trade off here. For linear lighting  applications  LEDs are significantly brighter and much more punchy. Colour  rendering  is  around  the  same as warm white LEDs, but lamp life and efficacies are back to halogen levels, and therefore relatively poor, but fibre optics still have their applications.

Cold Cathode

Cold cathode is a linear light source ideal for shadow free illumination of coffers and recesses. LEDs are comparable in terms of lamp life and colour rendering on warm white, and with further recent LED developments, efficacies of up to 55 lumens per watt are similar to cold cathode at 64 lumens per Watt for electronic systems.

Cold cathode is a glass light source and therefore carries a breakage potential and is often made to order, requiring  manufacturing times of around 4 weeks. LEDs are more robust and are available in much quicker lead times from acdc.

To create an equivalent output to cold cathode, light direction aside, a large number of LEDs are required spaced between 100mm and  50mm apart. Due to the number of LEDs required  to create an equivalent output, the LED solution can be relatively expensive initially,  but they may become a valid option. The vivid colours created by the LEDs can be very useful however, and they are excellent for colour change where three cold cathode lamps would be required. The small nature of the LEDs enables compact solutions to be developed for tight coffers especially in colour change details. For these types of applications, where three cold cathode lamps would be required, LEDs are definitely a valid alternative.

The efficacy of an LED should be considered, not just the Lumen output. Many LED suppliers quote high  power LEDs but  with  very low efficacies. Currently LEDs used by acdc have efficacies of 97 Lumens/Watt  for  cold  white  LEDs. The efficacy is continually increasing with the roadmap to double in output every two years. The LEDs used by acdc boast the highest efficacies currently available along with excellent lifetime performance. A common myth is that a 3 watt LED is brighter  than a 1 watt LED. This is often not the case and the true comparison is made using the Lumen efficacy of the LED.

Light Output Ratio is the ratio of the light output of a lighting  fixture to the total light output of the individual  lamp it houses. acdc’s optics are specifically designed to harness most of the light from the LEDs, around 90%; much more efficient than reflectors.

The simple answer is 50,000 hours.This is however the expected time taken for the light output of the LED to have dropped to 70% of it’s original value. It is likely that an LED will  continue  to light  for significantly longer than this but unlike a conventional bulb there is no sudden failure.

As a guide, using 1 Watt LEDs power consumption is 1.2 Watts per LED. The drivers are around 85% efficient, therefore the power consumption is approximately 1.4 Watts per LED.

However when considering an installation it is important to consider the power consumption of the driver in your calculations, as this value will allow for any relevant gear losses etc. These values can be found on acdc’s individual specification sheets.

CRI = Colour Rendering Index. This is the level to which  colours  appear  natural  under  a specific light source. A light source with CRI of 100 means that all colours will appear exactly as you would expect under normal daylight conditions. A warm white LED gives a CRI of approximately 90 which gives an excellent perception of colour. LEDs are currently under development with a CRI >95 .

Colour temperature of a light source is a way of comparing the whiteness of a light source. A low colour  temperature  (typically  3000ºK) gives  a warm  white   colour.  The  higher   the  colour temperature, the colder the light appears, with a cold white typically being 5000ºK or even 6500ºK. Colour  temperature  is  measured  in  Degrees Kelvin (ºK). This is related to the colour of light which would be produced by a tungsten filament lamp  with  the  filament  at  the  specific  colour temperature using the Kelvin temperature scale.

The hotter an LED gets the shorter it’s life will be. acdc design  products  with  this  in  mind  to ensure the typical lifetime  of it’s products  is in excess of 50,000 hours. High output LEDs will get extremely hot if they are not thermally bonded to a heatsink structure. This extreme temperature would cause rapid degradation of the LED. acdc incorporate the heatsinks into the design of the product   housing   which   ensures  the  overall fittings and the LEDs keep relatively cool.

Many other manufacturers do not consider the thermal requirements of LEDs and simply retro fit LEDs into cheap housing’s  which  dissipate heat poorly. This does impact the performance of the LED over its lifetime with many failing prematurely.

Although  this can vary throughout the acdc range, depending on the size of fitting  and number of LEDs used, the average is around 60ºC based on an ambient temperature of up to 40ºC.

acdc’s fittings  are designed to operate in an ambient temperature  of up to 40ºC. The storage temperature of an LED is considerably higher – in the region of 80-90ºC, therefore fittings can be used in Middle East applications for example, providing they are not  operating  during  daylight  hours. If there are concerns on a specific  installation,  we can provide onboard thermal cut-out solutions to protect the fittings  from operating in error during these hot hours.

During  the manufacturing of LEDs a range of shades of colour are produced. These are then ‘binned’  into sets of LEDs with similar colour properties. The more stringent the colour binning process, the less likely a colour difference will be seen between individual LEDs.

acdc are currently working with major LED manufacturers to improve the quality of this colour binning  process, however in the meantime acdc only purchase specially colour binned  LEDs and then  sub  divide  these  colour  bins  into  further colour bins to ensure only products with accurately matched LED colours leave the acdc factory.

Colour  shift  occurs  with  all  light  sources over time. Typically if any bulb is replaced it will appear a different  colour to adjacent bulbs. The colour shift  pattern  of LEDs is only very slight  and is virtually eliminated with correct thermal management of the fittings. Dimming can cause colour shift with conventional light sources (if you dim a filament/ halogen bulb down it appears red). This  is not  experienced  with  LEDs due to the special techniques used in LED dimming systems.

Yes there are a whole host of different  power LEDs available. Ranging from 0.01W right  up to several hundred  watts. There has even been a 1kW LED produced. The higher power LEDs are generally not a single LED but rather an array of lower power LEDs which  are combined over an area to give the perception of high power. It is not the  power  of the  LED which  is important  but rather the amount of light produced. The amount of light  produced is measured in Lumens. There are many low quality  5W LEDs which  produce significantly less light than quality 1W units.

acdc currently offer LEDs which can operate at 350mA and 700mA. acdc are committed to providing long life solutions  and  therefore  only  offer  products  at 700mA that are capable of coping  with  this increase in power and can dissipate the heat effectively.

NB. While output  can increase from 107 lumens  (350mA cold  white)  to 190 lumens (700mA cold white) the overall efficacy of the LED reduces from 97 lumens per watt to 72 lumens per watt due to the increase in power consumption.

Yes. acdccan currently provide LED drivers which can be dimmed using the following methods:-• DMX (digital  addressable dimming)  – hi-tech with individual control of each driver; dimmable to 0%

• Mains trailing  edge dimmable (traditional  type dimming) – used with incandescent light sources dimmable to 20%

• 0-10V  –  typically   found   with   fluorescent installations but this allows a low cost and efficient  dimming system to be utilised; dimmable to 10% at 0 volts

• Self cycle RGB is a simple colour change driver, with remote control options.

• Dali – excellent control down to 0% – outstanding dimming

The range of optics is always increasing. acdccurrently  offer the following  as standard options and now specify full beam angles.• Uncollimated  (no optic) typically  a 120 degree beam angle

• 12 degree full beam angle – 12R

• 18 degree full beam angle – 18R

• 30 degree full beam angle – 30R

• 50 degree full beam angle – 50R

• 45×10 degree full beam angle – 45 x 10R

All of the products in the acdc range have been independently photometrically tested, with different colour options and optics available. These are regularly updated as the LED technology begins to improve and outputs increase. Files are available in IES and LDT format on each products web page.