1. What is an LED and how does it work?
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.
2. How are LED colours created?
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.
3. How is an LED installation wired?
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.
4. How do LEDs compare to other light sources such as:
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 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 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 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.
5. What is a typical lumen output and when will it become a more usable light source?
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.
6. What does LOR stand for and what is the value for 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.
7. What is the average life expectancy?
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.
8. What is the energy / power consumption?
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.
9. What is CRI and what does it mean for LEDs?
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 .
10. What is colour temperature or what does Kelvin mean when referring to light sources?
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.
11. Does an LED get hot and do you have to consider the thermal issues?
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.
12. What sort of temperature does an LED housing get to?
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.
13. What is the maximum operating temperature an LED can operate in?
14. What is colour binning and how does it affect me?
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.
15. Does a colour shift occur in the LED over time?
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.
16a. Are 2 Watt, 3 Watt and 5 Watt LEDs available?
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.
16b. Do acdc offer a range of different LED powers?
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.
17. Can LEDs be dimmed and to what level?
18. What choice of optics are available and what is their performance?
19. Are LDT or IES files available for the acdc range?