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LED 2


What is an LED?

An LED, or light-emitting diode, is a semiconductor device that emits visible light when an electric
current passes through it. Normally the LED consists of several layers of semi conductor material,
with the colour emitted from the LED dependant upon the material used.

How are different coloured LED's created?

For most LED's, the colour is determined by the semi conductor material, not by artificial means.

How is White Light produced in a LED?

To produce white light, a phosphor is introduced into the LED which becomes "excited" when
combined with the light emission from a blue diode. This combination produces yellow light.
The amount of phosphor can be varied so that when the blue light is mixed with the yellow light of
the phosphor, various colour temperatures of white light can be produced.

What is SMD?

Generally, this means a Surface Mounted Device, such as an LED chip placed directly on a
surface of a tape or strip.

What is COB?

Generally, this means Chip On Board which can be specifically related to an LED chip placed
directly onto an electronic circuit board.

How important is heat sink?

Many inferior LED products have entered the market, where various claims are made relating
the the life and performance of the LED luminaire, or lamp. Essentially, whilst LED fixtures can
significantly produce less ambient heat than conventional light sources , LED's require suitable and
sometimes substantial heat sinks to ensure the efficient transmission and dissolution of the heat
produced by the chip, to protect the life and lumen maintenance of the LED chip.

What is a driver?

An LED driver is a self-contained power supply that has outputs matched to the electrical
characteristics of the LED chip, or array of LEDs.

What is Power Factor(pf)?

Power Factor is a term used to describe the relationship between the current and voltage in
an electrical circuit. Equipment such as ballasts possess inductance which causes the current
waveform to be displaced and 'lag' behind the voltage waveform.
A measure of this angle of displacement calculates the Power Factor. The larger the angle, the
lower the Power Factor.
An ideal power factor is when there is no phase angle difference between the current and the
voltage of the circuit and therefore the voltage and current are said to be 'in phase' at 'unity',
resulting in a power factor of 1.
LED products with a low Power Factor mean that the operating current has to be increased from
the supply source to compensate for the reduced Power Factor and to maintain constant power
at the load.

What is colour temperature?

Colour temperature refers to the warmth or coldness of the light produced by the lamp or LED,
measured in Kelvin (K). Lamps producing a warm or yellow light have a low Kelvin (2700-3000K),
while lamps producing a white or blue light have a higher Kelvin (3500-6500K). The ideal colour
temperature is dependent on the application.
Generally with LED, the higher the Kelvin rating, the higher the lumen output. But most times the
trade off is much poorer colour rendering (CRI) such as when items can appear very blue and
therefore not their true colour appearance.

What is colour rendering or CRI?

Colour rendition describes the effect a light source or LED has on the appearance of coloured
objects. The colour rendering capability of the LED is measured as the Colour Rendering Index,
or CRI.
When comparing the CRI of different light sources such as LED's it is important to note that
for the comparison to be meaningful, you should compare the LED's with the same colour
temperature.
The higher the CRI , the better the ability of the light source to depict a true colour comparison.
How do you measure the brightness of a lamp?
There are a number of different measures to determine the brightness of a lamp, however the
most common comparison will be the lumen output.
- Lumens
refers to the light output of a lamp or LED in all directions (think of an imaginary
sphere surrounding the light source and the light it is giving off in all directions)
- Candela
refers to the light output of a lamp in a single direction (think of a spotlight)
- Lux
is candelas, or light output in a given direction, measured at a specified distance
(think of the amount of light you may want at your work desk, as opposed to the amount
needed on the floor)
How do I measure the running costs of a 12W LED downlight compared to a 50W MR16

Halogen lamp downlight?

The running costs can be determined by the following.
Annual running cost $ = Wattage (expressed as a % of 1000 watts, or KW) x Hours (Number of
hours use per day) x cents per KWH (Cost of electricity)
Example:
What is the annual savings when I compare a Crompton 12W XL-LED downlight used for 10
hours per day, 7 days per week, 52 weeks per year, with the cost of electricity at 20 cents per
KW Hour ?
Annual Cost for Crompton XL-LED = 12/1000 x (10 x 7 x 52) x $0.20 = $8.74
Annual Cost for MR16 50W halogen downlight = 55/1000 x (10 x 7 x 52) x $0.20 = $40.04
*Full system losses have been used in the above example to more accurately reflect true
savings
Based on a medium sized house with an average of 30 x low voltage 50w halogen downlights
and a cost of electricity at 20 cents per Kilowatt hour, the annual savings would be more than
$900 per year.
Do I have to wait for my LED’s to light up to full brightness, such as with compact fluorescent
lamps?
No. LED’s give instant and immediate maximum light output.
Will frequent switching effect the life of my LED, such as with compact fluorescent lamps?
No. LED’s are unaffected by frequent on/off switching.
Can I use my LED’s in colder environments?
Generally, unlike that of most fluorescent lamps, LED’s have no problems operating at extremely
low temperatures (up to -30°C)

What is IEC?

International Electro Technical Commission

Can I run my LED MR16 style lamps on older halogen electronic transformers?

There are two basic types of LED drivers, both designed to run LED at their optimum parameters to
protect the life of the chip: constant current and constant voltage.
A constant voltage LED driver (ie. transformer) will output exactly 12V DC. 12V MR16 Style LED lamps
and other 12V powered LED modules can be connected in parallel to such a driver. Thanks to the
parallel connections, if one bulb dies, the remaining bulbs will stay on.
A constant current LED driver will output a fixed current, suitable for operation of the the LED chip
or module. The output voltage will vary as required to maintain the specified output current with
different forward voltage drops common with LED junctions.
Basically, the user needs to ensure that the LED supply you choose can handle the correct load.
Halogen transformers normally have a minimum load required and therefore (for example) placing
a 12V 3W MR16 style LED bulb on a 20-60va halogen transformer that previously operated a 50W
MR16 Halogen lamp is not an ideal solution, as the 'load' is not sufficient to start the lamp or run
the lamp at its optimum output.
A number of possibilities would generally be experienced with the above such as strobing or
flickering of the LED lamp or it may not work at all.
These characteristics can also be detrimental to the life span of the LED chip.
Due to the number of halogen transformers in the market with differing operating characteristics,
the best solution is to always ensure that the power supply has been recommended by the
manufacturer or supplier of the LED source, to ensure compatability.

What is DALI?

DALI is an acronym for Digital Addressable Lighting Interface and has become an open standard
for Lighting control Essentially, each light fitting is given a unique 'address' allowing digital control of the Lighting
installation.

What is DSI?

DSI is an acronym for Digital Serial Interface. It is a protocol for lighting control, through the controller
(mainly in commercial buildings). DSI was the first use of digital communication in lighting control,
and its low voltage means it can run on relatively thin cables. One of its main advantages is that it
dims to 'off' so does not require mains switching equipment to turn the lighting off.

What is the difference between DALI and DSI?

DSI is essentially the same technology as DALI in terms of digital communication, however DSI
eliminates the individual 'address' aspect of each light fitting required in DALI. In DSI each unit has
its own wire direct to the controller, rather than being part of a network such as with DALI.
 

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