Following are the advantages of PWM dimming:

Smooth dimming capability

More precise output levels

Better consistency in color over various levels

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.

CCR dimming is good in:

Outdoor applications and damp locations.

Places that have strict EMI requirements like medical suites.

Places where there is a lot of motion and rotary machinery.

Applications where the drivers are to be placed at long distances from the light source.

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

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.

Heat management is critical for the performance of LEDs. Increasing heat in LEDs has the following effects in performance characters:

• Reduction in luminous flux
  
• Color shift (change in color appearance)
  
• Reduction in life of the LED

The two-phase heat technique is a cooling technique that uses the advantages of both active and passive cooling methods.

It works on the principle of evaporation and condensation. The process requires disposable heat to initiate the process that happens in a hermitically sealed tube that is filled with a minute quantity of liquid. The system has cooling fins around the tube to dissipate heat. This system offers high reliability, zero operation costs and is not orientation dependent.

The following are types of optical systems of LEDs:

• Primary systems with integrated lenses - specific beam angles.
  
• Secondary optical systems in the form of lenses, reflectors or diffusers.
  
• Combinations of primary and secondary optics for specific applications.

Here are few of the ways in which glare can be reduced from LEDs:

• Use of microprismatic technology to develop special diffusers that disperses light from individual LEDs. This system gives out homogeneous light with optimum levels of contrast avoiding any direct or reflected glare.
  
• Design of secondary reflectors systems; where the primary reflector, which will hide the view of the LED and direct the light into the secondary reflector that will distribute the light in the intended way.

• Use of a combination of TIR (total internal reflection) lenses / collimator lens, which that produce a parallel beam of light, and a facetted lens. This combination will distribute the light beam as intended.
  

• The LED drivers can fail early due to ingress of moisture or condensation. The driver enclosure needs to be properly sealed to prevent this.
  
• LEDs are less resistant to damp than other light sources. This means that particular attention needs to be given to the light fixture seal and cable glands.

• Heat build up occurs as the luminaire is turned on, and as it cools down when it is switched off.

• Pressure changes caused by a change in altitude and environmental conditions during transportation in cargo holds or in planes.

• Thermal shock due to rain, snow or washing cycles.

• More rugged O rings and gaskets for more robust seals.
• Thicker enclosures to prevent movement around seals to prevent breakage of seals.
• Additional bolting around gaskets and seals to prevent snapping of seals.
• A vent made of two-way permeable membrane. This allows water vapor and gas to pass through but not liquid water.

Unlike conventional light sources that reduce in output and eventually fail, LED products do not normally suddenly fail. Instead, the light output reduces over time.

The normal convention is to measure the life from when the output has reduced by 30%, i.e. when there is 70% light output remaining. This is often quoted as the L70 life and is measured in hours.

The thermal management of the LEDs. If LEDs come on a standalone chip, appropriate heat sinks have to be designed to prevent premature failure of LEDs.

The electrical stress: Running LEDs at currents higher than specified make the LED run hot. This can happen with wrongly matched drivers. For example, if the driver produces 700mA but the LED needs 350mA, this will put stress on LED and reduce its lifespan.

Higher ambient temperatures than the ones that the LED is rated for will reduce its expected life.

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.

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

Luminous garments

LEDs do not directly produce white light. There are two ways in which white light is produced from LEDs as below:

Using a blue LED with a phosphor coating to convert blue light to white light by a process called fluorescence.

Combining red, blue and green LEDs to produce white light. White light is produced by varying the intensities of the individual red, blue and green chips.

The following are the different types of RGB LEDs:

• R/G/B/W - Has an additional white LED. This is often used where you need a pure white as well other combined colors.

• RGB / 3 in 1 LED - Uses a red, a blue and a green LED chip are mounted within a common light engine and focused through a lens to produce a more uniform hue across the beam of light.

• RGBW / 4 in 1 LED - similar to the RGB LED but with a warm white LED integrated in the light engine to offer more color tones.

• RGBA - Has an additional amber LED chip.

These are chemical symbols used for materials used in the manufacturing process of the LEDs to generate specific colors.

AlGaAs - Aluminium Gallium Arsenide used to generate red and amber portions of the visible spectrum.

AlInGap - preferred chip technology using Aluminium, Indium, Gallium and phosphorous to produce red, orange and amber colors.

InGaN - Indium, Gallium and Nitrogen to produce green, blue and white colors.

• Color Rendering Index - CRI indicates the accuracy with which a light source such as an LED can reveal the various colors of an object. The standard CRI system is based on eight colors across the spectrum.
   

• Additional R-values of CRI are used to represent certain colors. The appropriate R-values are application specific. For example R9 represents red and is good for lighting flesh. It also tends to make the light warmer.
   

• Color Quality Scale CQS is a new system that uses a wider palette of 15 reference colors against the smaller palette of 8 reference colors used for the CRI system.

Apart from CRI, R-values and CQS, color consistency is also a measure of the quality of light. The color consistency can be evaluated at several levels as follows:

• Consistency over time: Color shifts over the life time of LEDs.

• Consistency between different products and batches: Color tone variations from batch to batch.

• Consistency across the beam of light: Color shift across the beam of the LEDs.

• Consistency between color specification in the datasheet and that seen when the LED is used.

There are several possible reasons why this happens:

• The LEDs are being overrun by the use of an inappropriate driver.

• The application temperature is different from the operating temperature noted in the LED datasheet.

• There may be heat build-up due to improper thermal management.

• The phosphor may have degraded due to overheating or other reasons.

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.

Here are the various terminologies for developmental stages of LED in chronological order:
 

• LED Die - A small block of light emitting semi-conducting material on which functional LED circuitry is fabricated.
• LED Package - This includes an LED die or more than one LED die with an optical element and mechanical, thermal and electrical interface.
• LED 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.
• LED Engine - This is an LED module or array of packages with the associated control gear / LED driver. It is the nearest equivalent to the lamp in a conventional luminaire.

The advantages of SMD over DIP LEDs are:
 

• Smaller size
• More lumen output
• Better heat dissipation
• Lower lumen depreciation
• Longer life

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.
• MCOB (multiple chips on board) LEDs, which are multiple COB LEDs integrated to form a single chip. This technology is used in LED bulbs and tubes.
• MCCOB (multiple chips and cups on board) packages, which are used for high bay fixtures and floodlights.

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.
• Chip on board with an optical lens or diffuser as a prefabricated piece with or without integrated heatsink. That can be used by luminaire manufacturers to integrate into luminaire.
• Retrofit lamps to replace older (halogen) technology. This comes with an integrated heat sink and standard lamp base that can fitted directly into existing luminaires with a standard lamp holder.
• Prefabricated luminaires with an integrated LED light source and heat sink complete with luminaire housing that is available as a sealed piece. The driver may be integral in the housing or may be remote.

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.

Here are the general LED lighting facts:

• LED lighting does not contain mercury
• All white LEDs emit certain level of blue light, which is still only a tiny fraction of natural daylight
• General exposure to blue light is atleast 1000 times greater outsideduring summer days.
• Looking straight into the sun for 1 sec will have an effect on yoir eyes, for the similar effect you will have to stare at LED lighting (4000 K) for 30 min from a short distance.
• Blue light hazard is classified into 4 risk groups 0, 1, 2, 3 (0=low, 3=high) sun falls into group 2. Well tuned LED lighting belongs in category 0.
• Visible flicker is known for potentially causing epileptic seizures whereas non visible flicker will not.
• Visiblke strobe is belived to cause eyestrain, discomfort, headache and reduced visible performance whereas non visible strobe is believed not to.
• Glare can generally be put in 3 categories when assessing its influence on people - blinding, disability and discomfort.

These are some LED lighting benefits:

• LED lighting can support one's visualpsycological and biological values - Scientific studies indicate that tailored indoor applications are linked to enhanced vision, performance and well being.
• Organizations that implement LED lighting in office spaces and work areas have recognized an increase in employee effectivity, workplace satisfaction and visual comfort.
• When LED lighting is applied in a learning environment research suggests that concentration of children goes upto 20%, literacy skills are improved and fidgeting is reduced.
• LED lighting  can boost our mood and positively impact our behaviour
• LED lighting can contribute to a healthy circadian rhythm
• Blue light helps children and adoloscents feel more awake in the mornings.
• Bue light also helps with enhancing one's concentration ability.
• Dimmed LED lighting can enhance creative thinking
• LED lighting has been associated with decreased levels of stress and anxiety in indoor environments

Staring straight into a strong LED Light with a high color temperature (expressed in Kelvin) at a close distance for a long period of time can possibly damage the retina. Normally, the discomfort experienced will require to avert or close the eyes, preventing any damage.

These are the factors in play:

• Level of luminance
• Spectral distribution
• Exposure time

The journal article (Photochem. Photobiol. 89, 468-473) shows the experiments exposing human eye cells to light intensity of 5 mW per square centimeter for twelve hours, which leaves noticeable damage behind. However, for a typical white LED spectrum, this intensity level corresponds to staring directly into a 100-Watt-equivalent light bulb from about 10 centimeters away, for twelve hours straight.

• Some say LEDs are damaging to preservation of collections and other objects – this is not the case. LED lights do not emit ultra violet radiation. Consequently, they are safer for collections preservation than fluorescent lights.
• Fading as a damage factor could apply to short-wavelength lighting, which could relatively damage/discolor, depending on the exposure time, illumination level, and object sensitivity. Mostly due to UV radiation. 
• Besides the benefits that come along with LED lighting, the potential negative effects only persists in case of repetitive excessive (direct)exposure under unfavorable circumstances.
• Apply the right light, with the right spectrum at the right time during the day is highly beneficial, one of the reasons what makes LED lighting so valuable.

No. If properly designed and applied, LED lighting will provide its advantages and you can avoid potential unwanted side effects.

If you apply the right light, in the right place, at the right time, for the right situation, LED light can positively impact public safety and liveability while also offering savings on energy and maintenance. Philips Lighting solutions are carefully designed for local applications taking into account the right optics and light intensity to benefit from the LED advantages and mitigate negative effects like circadian disturbances and glare.

There are several good examples from the current Philips Lighting customers including:

• Los Angeles, CA
• San Jose, CA
• Macon-Bibb county, GA
• Jakarta, Indonesia
• Grand-Prix, Singapore
• Buenos Aires, Argentina