Frequently Asked Questions
What are LEDs?
LEDs are light emitting diodes. These are electronic components that convert electrical energy directly to light through the movement of electrons within the material of the diode. LEDs are important because due to their efficiency and low energy, they are beginning to replace most conventional light sources.
Why is LED technology classified as solid state lighting?
The term solid state lighting is used because the electronics produce light directly from solid materials in which the electrons are embedded. This is unlike other technologies, for example, fluorescent technology, which requires a gaseous discharge medium to initiate production of light.
What does “future-proofing” of LED products mean?
LED technology is constantly changing. Rapid innovation continues to improve the performance of LED on an almost daily basis. Future-proofing of LED modules allows luminaire manufacturers to switch from one generation to the next improved generation without major retooling or changes in luminaire design, offering backward compatibility with drivers.
What is binning?
LED chips are mass produced in millions and there are inevitably slight differences in color appearance and light output. Binning is way of sorting the chips so that all the LED from one particular bin look the same and have similar light output.
What is a light engine?
A light engine is the LED equivalent of a conventional lamp. It normally consists of a LED chip mounted on a circuit board that has electrical and mechanical fixings, meaning it is ready to be fixed in the luminaire . Note that the light engine may not consist of only one chip; it may be an array of 9 or 16, sometimes with a phosphor coating.
What makes LEDs more robust than other light sources?
LEDs have no gases, filaments and no moving parts to fatigue. They provide light through a one-step process that takes place within the diode. There is no glass to break or screwed contacts to loosen.
Why do LEDs have a higher initial cost than conventional light sources?
LEDs are made of electronic components that need to be packaged together to offer long lasting efficient light sources to the end user. Apart from the LED chip itself which has sapphire and gallium in the semiconductor, the process of packaging with materials like ceramic, rare earth phosphors, silicone, solder and gold wire add to the overall cost. White LEDs require further tests for calibration and standardization.
What are the economic advantages of using LEDs over conventional light sources?
Although the initial cost of conventional light sources is less than LEDs, the operational and maintenance costs of LED are significantly lower. LEDs, having a longer life, reduce maintenance and lamp replacement cost. . Because LEDs need to be replaced less frequently, the owner spends less on new lamps and the labor needed to change them. LEDs also consume less energy; thus the overall cost of a LED system can be significantly lower than that of conventional lighting systems. Most applications with LEDs offer a payback period as low as three to four years.
What are the strategies in the development of LED technology that are helping to reduce the cost of LEDs in the future?
Some of the strategies for reducing the cost of LEDs in the future are:
Reduction in the production process.
Simplification and reduction in the number of components.
Introduction of new materials.
How do LEDs produce light?
How is light produced in an LED?
Light emitting diodes produce light by the movement of electrons between the two terminals of diode, which occur by a process called electroluminescence. When a light emitting diode is electrically connected, electrons start moving at the junction of the N-type and P-type semiconductors within the diode. When there is a jump over of electrons at the p-n junction, the electron loses a portion of its energy. In regular diodes this energy loss is in the form of heat. However, in LEDs the specific type of N and P conductors produce photons (light) instead of heat. The amount of energy lost defines the color of light produced.
What are the core components of a typical LED that gets soldered to a Printed Circuit Board?
A typical LED is made with a chip, which is the semiconductor that produces the light when electrically connected. The chip is connected by a very thin bond wire to a lead electrical contact that acts as the cathode. The chip is bonded with a thermal heat sink and a ceramic base. The chip is enclosed by a lens that not only protects the chip, but also modulates the light beam to the desired angle, depending on the nature of the lens. For production of white light, the chips are coated with phosphors.
How are LEDs different from other light sources in the way they produce light?
LEDs produce light by direct conversion of electrical energy to light energy.
On the other hand incandescent light sources produce light by heating a filament until it grows red hot. Linear and compact fluorescent lamps use a UV discharge plus a phosphor to produce the light. HID lamps use the ionization of gases in a discharge tube which in turn produce photons.
Do LEDs require time to reach maximum brightness?
No. LEDs directly convert electrical energy to photons. It is a one step process of electroluminescence that does not require time to reach maximum output. Other sources such as fluorescents or HID, work on discharge technology. This requires an arc to warm up and may take a few minutes to reach full output.
What are O-LEDs?
O-LEDs are organic light emitting diodes. They are made of carbon based films sandwiched between two electrodes; one is a metallic cathode and one is a transparent anode, which is usually transparent glass.
What are the characteristics of O-LEDs that make them different from other light sources?
O-LEDs are thin, flat, two dimensional surfaces offering a soft, glare-free luminous surface. Some versions of OLED are flexible. They can be transparent, mirrored or diffused when not electrically connected.
What are some new uses of LEDs that have appeared with the advent of OLED technology?
With the further increase in performance characteristics of LEDs and the advent of OLEDs the application sector of LEDs has expanded. Below are some of the new uses of LEDs:
Luminous walls and ceilings
Transparent walls and partitions that turn opaque at different times of the day.
Solar powered fabrics
Dimming with LEDs
How are LEDs dimmed?
LEDs are dimmed either by Pulse Width Modulation PWM, or by Constant Current Reduction CCR. PWM dimming involves switching current at a high frequency from zero to the rated output current. CCR dimming: The lighting level required is proportional to the current flowing through the LED. Current flows through the LED continuously and is reduced or increased based on whether the LED is to be dimmed further or made brighter.
What are the relative advantages of PWM dimming?
Following are the advantages of PWM dimming:
Smooth dimming capability
More precise output levels
Better consistency in color over various levels
What are the disadvantages of PWM (pulse width modulation) dimming?
Following are the disadvantages of PWM dimming:
Relatively more expensive
Flicker perceived in peripheral vision if the driver is run below 100Hz frequency
Stroboscopic effect evident in fast moving environments when the driver frequency is low.
Electromagnetic Interference (EMI) issues due to rise and fall of the current in PWM dimming.
Performance issues arise when the driver is mounted remotely from the light source.
Can mains voltage LED products be dimmed with traditional incandescent dimmers?
Although LED products are marked as compatible with traditional dimmers, there are various degrees to which LED products are compatible with incandescent dimmers. Compatibility needs to be checked and tested on a product by product basis for the following most common undesirable behaviors:
Reduced dimming range
Flickering of the lamp
Inconsistent performance based on the number and different types of LEDs connected to a single incandescent dimmer
What are the advantages of dimming LEDs?
Dimming LEDs offer the following advantages:
Saves energy, because less energy is used for reduced output levels.
Extends life; the electronic components run cooler. This not only extends the life of LEDs but also increases the life of the phosphor coating that is used to produce white light.
Helps designers create ambient lighting presets to create mood settings.
Increases flexibility in usage of space. A brightly lit space for reading or an office space can turn into a presentation/conference area by dimming.
Increases productivity by enabling individual control of lights in order to reduce eye strain and fatigue, or to improve concentration.
What are the various control protocols that can be used for dimming LEDs?
LEDs are controlled directly by signals coming from the central dimmer. They can also be designed to interpret other protocols like 1-10V, DMX, Ethernet or ZigBee signals from the central dimming system. The manufacturers of LEDs will specify which of the various protocols their devices can understand.
What is the difference between analog and digital dimming?
Analog dimming is usually referred to as 1 - 10v dimming. In this case, a dc voltage is sent to the driver, which dims the LEDs in response to the voltage. With digital dimming, the driver receives a digital signal which tells it how to respond. The advantage of digital dimming is that fixtures are addressable. You can also have many more different levels of light output when using digital dimming.
What lighting protocol is appropriate for an application?
For applications where single colors and white LEDs are used, analog or PWM dimming protocols can be used to switch or dim LEDs. For intelligent controls like creating dynamic effects, tuning of white light etc, DMX or Ethernet protocols can be used. Digital dimming works better with large numbers of luminaires.
Why do some LEDs flicker when dimmed or turned off?
This is usually due to incompatibility between the driver and the control system. When purchasing an LED product, it is important to use the correct driver type as specified by the manufacturer. It is also important to check that the LED is dimmable. Some retrofits are not.
What are the advantages of using a remote phosphor process compared to using phosphor coated LEDs?
The remote phosphor process offers:
Longer lifespan, as it reduces temperatures and slows down the rate at which the phosphor layer degenerates.
Increased system efficiency with reduced operating temperature of the system.
Better color stability with longer life of phosphors.
Less glaring than phosphor coated LEDs
More consistent flux output and correlated color temperature for the products, since LEDs from various bins can be used to produce light with consistent characteristics using the remote phosphor process.
What terms describe the different forms of LEDs from (basic electronics to fully functional light fixtures) that are available in the market?
Here are the various terminologies for developmental stages of LED in chronological order:
Die - A small block of light emitting semi-conducting material on which functional LED circuitry is fabricated.
Module - This includes and LED package or an LED die, possibly with an optical element connected to a circuit board, and with thermal, mechanical and electrical interface that are intended to be connected to the load side of the driver.
What does SMD mean?
SMD means surface mounted diode. This is a better technology than the first generation DIP LEDs. The SMD type LEDs are mounted on an aluminum substrate and enveloped in an epoxy resin.
What are the advantages of SMD over DIP LEDs?
The advantages of SMD over DIP LEDs are:
Better heat dissipation
Lower lumen depreciation
What are the various types of LED chip packages available in the market?
The basic types of chip LEDs are:
SMD (Surface mounted diode) is a standalone chip on a ceramic base that can be integrated into various packages for linear LED strips or downlights.
COB (chip on board) LED, which comes as a high powered chip in direct contact with a printed circuit board optimal thermal management.
MCCOB (multiple chips and cups on board) packages, which are used for high bay fixtures and floodlights.
What are the typical types of LED modules available in the market?
LED modules may be available in the following forms:
Prefabricated chip on board which can be used for specific applications by luminaire manufacturers who design the heat sink and mounting conditions.
Which developments in LEDs have reduced the number of components in a system?
The chip on board (COB) package enables mounting of the package directly onto a heat sink instead of relying on a LED board manufacturer.
In many designs the heat sink is designed to be a part of the luminaire housing design, which reduces the number of components in the system.
The development of more stable mains voltage AC LED drivers is leading to solutions that can reduce wiring requirements and overall dimming cost.
What is ZigBee?
Zigbee is a technology developed by a global alliance of companies to create wireless solutions for energy management. These solutions which include a new open standard for LED lighting controls.