SMD LEDs actually consist of two main parts: the epi-wafer and the packaging. The epi-wafer is an incredibly small piece of electronics and the packaging is everything around it... that white plastic, with a small heat-sink and that yellow-looking surface. There are relatively speaking very few LED epi-wafer manufacturers - names like Epistar, Cree, Bridgelux, Osram, Nachia, Samsung dominate in terms of quality, and most of these are not Chinese. There are hundreds of chip packagers (encapsulators) and many of these in China. They purchase the epi-wafers and package them into an SMD LED or a DIP LED. Whilst the quality of the epi-wafer is incredibly important, so too is the quality of the packaging. Quality packaging contains gold wire used to mount the epi-wafer and a high quality phospher mix, the yellow substance. The phospher mix determines the quality of the colour, in terms of CRI as well as the quality of the colour produced.
The efficiency of an LED luminaire can be measured as the amount of light produced for the electrical power consumed - lumen / watts. The higher this number the more efficient the luminaire is. An efficiency over 100 lumen / watt is deemed to be good. This is what makes LED technology so attractive: you can reduce your electricity bill. An incandescent bulb generates around 13 lumen per watt whilst an average LED lamp will generate upwards of 70 lumen / watt. The difference is usually in the heat produced: an incandescent bulb is in essence a small heater whereas an LED runs much colder. In 2012 MIT scientists invented an LED which has an efficiency of 230% meaning that it generated more protons of light than the electrons it consumed; as it started to exceed 100% efficiency is consumed heat from the surrounding air. You can read about it here.
Surface mounted technology (SMT)
Surface mounted technology represented a major leap forward in how electrical circuits were built. In the past a circuit board was a thick non-conductive board with a copper circuit etched on the back side. Components were placed on the top side of the printed circuit board (PCB) with metal legs protruding through holes to the back of the board where they were soldered onto the copper circuit. This technology did not allow for the levels of component density required for modern electronics, and scientists discovered ways of placing much smaller components directly onto the circuit and soldering them in place using a solder paste and heat. Placing such small SMD components onto circuit boards accurately, in a mass production environment now required accurate machinery. SMT machines are able to be programmed to place the required SMD component onto a circuit board in the exact location, before the boards enter a reflow solder machine for the components to be permanently fixed onto the boards. Components could get smaller, allowing for both more components per square inch of board, but also for circuitry to get smaller allowing for smaller electronic devices.
Surface mounted device (SMD)
A surface mounted device is really the same as an SMT component. The LEDs used on most modern lumaires are generally SMD LEDs.
Colour rendering index (CRI)
The colour rendering index is a measure of how close white light is to natural light emitted by the sun. It is measured on a scale of 0-100 with 100 representing sunlight - meaning that light with a CRI of 100Ra will light objects exactly as the sun would. Achieving a CRI of 100 has not yet been achieved with LEDs however it is possible to get LEDs with a CRI of around 95Ra although these are expensive and rare. A high CRI is valuable where trueness of colour is important, such as in photo editing environment or even jewelry stores.
Correlated colour temperature (CCT)
CCT is the colour temperature of light. Sounds odd, but the colour of light is referred to as a temperature, in Kelvin (K) and depicted on the colour spectrum. We refer to natural white as being around 6000K, warm white as being around 3000K. It's important to choose the right colour temperature for your lighting project: warm white is more "homely" but a little dull, has a tint of red in it, whilst pure white is clinical, but good for reading, good for stores. When replacing your downlight bulbs you need to check the blown bulb for the CCT, usually will be written on the bulb, so that you can match the colour, lest you want some pure white bulbs, some warm white bulbs, and they will definitely all look different.
Luminance is the measure of brightness of light, usually measured in lumen (lm). The higher the lumen the brighter the light. There are a few ways of increasing brightness in an LED luminaire: using a good quality epi-wafer, a larger epi-wafer, increasing the current to the LED (reduces the brightness of the LED over time), using a good quality phospher or simply adding more LEDs.
Flexible printed circuit (FPC)
An FPC is a very thin, bendable circuit board on which electrical components (resistors, ICs and LEDs) are mounted to produce LED flexible strips. They are usually made of copper. Not all FPC is equal. Most of the flexible strips sold in South Africa uses very thin FPC, which is prone to breaking, conducts electricity poorly and conducts heat poorly. All LUMUL products with an FPC use a double layer of copper, and a minimum of 2oz of copper, which actually means the copper is about 68µm thick. Still incredibly thin but an FPC this thick would conduct heat away from the SMD LED thereby improving the lifespan of the LED and will also conduct electricity much better, for more even light across the length of the strip. The second factor to consider is the width of the FPC. A wider FPC contains more copper, hence even better heat dissipation. That's good.
LED flexible strip
LED flexible strip is one of the most innovative LED lighting applications in recent times. A circuit board is printed on an FPC (see above) upon which SMD components are mounted and soldered. LED flexible strips can be manufactured to operate in different voltages, usually they would be 220V, 110V (for the US), 36V, 24V and 12V. The higher the voltage the more efficient the strip, the lower the voltage drop, but the more dangerous the strip is. 220V strips are generally only available in IP67 / IP68 silicon sleeves for safety reasons. Interestingly, all LED flexible strips operate at 5V internally, so the 220V strips require converting from AC to DC (in a converter) and then all the flexible strips require stepping down from the higher voltages to 5V. All flexible strips can be cut at demarcated points, and re-joined, providing flexibility in installations. The higher the voltage strip the greater the cutting length, for example a 220V strip can usually be cut every 1m (many diodes per cutting unit), whereas a 5V strip could be cut after every LED, since there are no resistors on the strip. Before you go out seeking 5V strips be aware they are only available as a custom order and can not be run very long due to voltage drop.
Voltage across a length of wire will inevitably experience a drop: meaning that whilst you may have for example 12V at the start of the wire, you might only measure 11V at the end of the wire. The higher the current, the longer the wire (conductor) and the thinner the wire (conductor) the greater the voltage drop will be. This means that the higher the voltage, the less chance of voltage drop, the thicker and wider the FPC the less chance of voltage drop. In the case of LED flexible strips and LED Neon Flex, this translates into shorter lengths of lighting which could be run in series. As a rule of thumb, a 12V flexible strip can only be run for 10m whereas a 24V flexible strip can be run for 20m, without noticeably dimmer LEDs at the end of the strip as at the start. 220V LED Neon Flex can usually be run for a length of 100m.
An LED driver is merely a power supply. Most purchased LED luminaires are generally available in 220V, 110V, 24V and 12V. 220V luminaires, for example a floodlight or a 220V downlight bulb, contain a built-in power supply, whereas 24V and 12V luminaires require an external power supply. Some LED luminaires require a constant voltage power supply and others require a constant current power supply. To realise the long lifespans which LED manufacturers lay claim to, of 30000 to as much as 100000 hours, you need to ensure you use a quality power supply since power supplies are the weak link. The reason your 220V downlight never lasts the advertised 3-5 years is simply because the built-in power supply is cheap and nasty. Always opt for an external power supply if you want your LED lighting installations to last.
The quality of an LED driver is a factor of a few key criteria: the quality of the component used and the efficacy of heat dissipation. Power supplies contain a few capacitors, and not all capacitors are equal. The Japanese manufacture the best capacitors in the world: they are expensive and they have a short shelf life when not being used. Hence they are expensive for power supply manufacturers to work with: they need to order as they require, which pushes up manufacturing lead times and pushes up the cost of the power supply. There are other components as well, where expensive components improve the performance of the power supply. Heat is the enemy of most electrical components, and as most people know, power supplies often get quite warm. It is essential to draw the heat away from the components as effectively as possible. As such, IP67 power supplies will have a longer life span as they are filled with silicone which is highly effective at drawing away heat from the components. Metal-case power supplies will also dissipate heat better than a plastic case.
LED driver efficiency is a % of how efficient the power supply is at converting input electricity into output electricity. A good design with good components will tend to be more efficient, and will sadly cost you more. Efficiency is important for two reasons: an efficient power supply will reduce your electricity consumption which becomes important when your luminaire is lit for hours on end, such as with signage, plus the energy not converted into output power is released as heat. So a less efficient power supply will run hotter - requiring more heat dissipation.
Good LED drivers will contain built-in protection for over-current and under-current, as well as electrical spikes, and even lightning strikes. This is incredibly important when you consider how poor the quality of our electricity supply from Eskom and municipalities, where the polarity is often switched, we get frequent spikes which often fry people's electrical equipment.
Constant current and constant voltage
There are generally two types of low voltage LED luminaires (those not containing an in-built driver): constant current and constant voltage. The difference is that they require different types of power supplies or drivers. A constant current LED luminaire requires the same current to be provided to it at all times, and the voltage required may fluctuate, whereas a constant voltage luminaire requires a constant voltage to be supplied to it, irrespective of the load. This is important since a constant current luminaire requires a constant current LED driver, and a constant voltage luminaire requires a constant current driver. You can not mix the two without damaging the luminaire or driver. Most LED luminaires, such as low voltage downlights, require constant current drivers, whereas most LED flexible strips and LED Neon Flex require constant voltage drivers. Constant current linear luminaires don't suffer from dimmer lights at the end of a long series since the luminaire circuitry caters for a higher voltage at the start and a lower voltage at the end, but the exact current needed for the LED.
Dimming sadly seems to have been an after-thought in the LED industry. Not all LEDs that you purchase can be dimmed, especially not those containing a built in power supply. You cannot use the in-wall light dimmers which were so popular with incandescent and CFL bulbs. Some low-voltage LED lights can be dimmed by using a dimmer (rheostat) between the power supply and the LED light, however if your LED light requires a fair amount of power, for example 5m of LED strip (possibly 72 watts in total) your rheostat will be incredibly bulky and expensive.
There are generally 6 ways of dimming an LED light: 0-10V, 1-10V, PWM, resistance, DALI and TRIAC. Dimmable power supplies provide a mechanism for dimming low voltage lights by supporting one of the above-mentioned dimming protocols. These power supplies have two input cables: one for 220V electrical input and one which is used for dimming control. The power supply will process the dimming control input and dim the output accordingly.
International Protection Market / Ingress Protection (IP)
A world-wide standard, IEC standard 60529, was created to enable a uniform rating of the dust and water protection capabilities of a product. The most common ratings you will come across in the LED lighting world are:
IP20 - dust proof
IP65 - water resistant - can withstand water splashing onto the object, such as rain
IP67 - water resistant up to 1m under water
IP68 - water resistant up to 10m under water
The Conformance European (CE) mark of certification means that the product complies with all EU regulations, including for quality and safety.
The Restriction of Hazardous Substances (RoHS) mark means that the product complies with international standards for hazardous materials. Products carrying this mark will not contain materials such as mercury or lead, which many of the older, and more regular lighting products contain. For example, your regular floodlights contain mercury, as do glass neon signs.
The Underwriters Laboratories Inc (UL) mark indicates that the product conforms to all US regulations of safety and quality. The USA is a highly litigious country and as such the UL standard is far more onerous than the CE standard.