What Is An LED ?
An LED or Light Emitting Diode is a semiconductor device which uses a “P-N junction”, which emits light when energized by electrons.
LEDs emit light when an electric current passes through them.
LEDs emit light when an electric current passes through them.
Fig01. LED
Fig02. LED Symbol
Fig03. LED Construction
Fig04. LED die
The basic LED construction consists of an LED die (this is the semiconductor which emits the light) which is mounted by conductive epoxy and a wire bond onto a lead frame (metal legs) which allows connection of the die to the external power source.
Fig04. LED die
LED die are small, a typical die maybe only 0.2mm x 0.2mm square.
Colours of LEDs
LEDs are available in red, orange, amber, yellow, green, blue and white. Blue and white LEDs are much more expensive than the other colours.
Fig05. Colours of LED
Colours of LEDs
LEDs are available in red, orange, amber, yellow, green, blue and white. Blue and white LEDs are much more expensive than the other colours.
Fig05. Colours of LED
The colors is defined in the manufacturing process and is normally specified in nanometers (nm) which is the spectral wavelength of light the LED emits. For example a Blue LED would be 470nm.
The colour of an LED is determined by the semiconductor material, not by the colouring of the 'package' (the plastic body). LEDs of all colours are available in uncoloured packages which may be diffused (milky) or clear (often described as 'water clear'). The coloured packages are also available as diffused (the standard type) or transparent.
Brightness has traditionally been measured in mill candela (mcd). This is a measurement of light taken at a fixed point. It is different to bulbs which are normally measured in Lux which is a measurement of total light output.
Brightness in datasheets varies greatly from one manufacturer to another as the mcd figure is relative and no standard exists for this measurement so each company uses its preferred method. This makes comparing the actual brightness of an LED difficult on paper without testing the specific device in the application.
The LED industry moves more into the traditional bulb areas they are beginning to specify many of the LEDs in luminous flux, lumens (lm), which is a total light output measurement.
The colour of an LED is determined by the semiconductor material, not by the colouring of the 'package' (the plastic body). LEDs of all colours are available in uncoloured packages which may be diffused (milky) or clear (often described as 'water clear'). The coloured packages are also available as diffused (the standard type) or transparent.
Brightness has traditionally been measured in mill candela (mcd). This is a measurement of light taken at a fixed point. It is different to bulbs which are normally measured in Lux which is a measurement of total light output.
Brightness in datasheets varies greatly from one manufacturer to another as the mcd figure is relative and no standard exists for this measurement so each company uses its preferred method. This makes comparing the actual brightness of an LED difficult on paper without testing the specific device in the application.
The LED industry moves more into the traditional bulb areas they are beginning to specify many of the LEDs in luminous flux, lumens (lm), which is a total light output measurement.
Tri-colour LEDs
The most popular type of tri-colour LED has a red and a green LED combined in one package with three leads. They are called tri-colour because mixed red and green light appears to be yellow and this is produced when both the red and green LEDs are on.
Fig06. Tri Colours LED
The most popular type of tri-colour LED has a red and a green LED combined in one package with three leads. They are called tri-colour because mixed red and green light appears to be yellow and this is produced when both the red and green LEDs are on.
Fig06. Tri Colours LED
The diagram shows the construction of a tri-colour LED. Note the different lengths of the three leads. The centre lead (k) is the common cathode for both LEDs, the outer leads (a1 and a2) are the anodes to the LEDs allowing each one to be lit separately, or both together to give the third colour.
LED voltage and polarity
The operating voltage of an LED or its Forward Voltage (Vf) depends on the type. Typically this is between 1.7 volts and 3.6 volts. It is important to make sure this is not exceeded by using some form of current limiting to protect the LED from internal damage. Once you have considered current limiting the LED can operate from a wide range of voltages.
The operating voltage of an LED or its Forward Voltage (Vf) depends on the type. Typically this is between 1.7 volts and 3.6 volts. It is important to make sure this is not exceeded by using some form of current limiting to protect the LED from internal damage. Once you have considered current limiting the LED can operate from a wide range of voltages.
Fig07. LED polarity
Why Use LED’s ?
Basic LED Types
There are four common LED types.
Why use LEDs as your light source? Here are some of the key benefits.
Robust & Shock Resistant
LEDs are solid state devices which have no filaments or glass tubes to break.
Long Life
Depending on the type, typical life for an LED can be 50,000 hours (5 years+) to 100,000 hours (11 years+) continuous operation.
Energy Efficient
LED’s do not waste energy as a filament does which has to be first heated until white hot to emit light.
Low Voltage
LEDs can operate from as little as 5 volts but can easily be configured to work from a wide range of voltages to suit specific designs or available power supplies.
No Colour Fade
An LED is designed to emit a specific wavelength of light. This is defined in the LED manufacturing process, they do not rely on colored filters or gels to produce a specific color which could fade over time.
Fit and Forget
LED’s are low maintenance devices and require no servicing during their life.
Simple Installation
LED’s don’t require any special driver circuits, starters, chokes or inverters to operate. They are fully dimmable and can be controlled with simple electronics.
Wide Range of Colors
The basic LED colors are red, orange, amber, yellow, green, blue and white. Within each colour we can offer a range of shades.
Slimline Design
LEDs are physically smaller than many traditional light sources and allow unobtrusive slimline designs to be made.
Sealed Units
LEDs do not need to be changed as with fluorescent or filament bulbs so there is no need for a bulb holder / fitting or the need to make the enclosure accessible for changing the bulb. This simplifies product design as the unit can simply be potted in a clear resin to seal the unit. This also makes the unit tamperproof and more vandal resistant.
Robust & Shock Resistant
LEDs are solid state devices which have no filaments or glass tubes to break.
Long Life
Depending on the type, typical life for an LED can be 50,000 hours (5 years+) to 100,000 hours (11 years+) continuous operation.
Energy Efficient
LED’s do not waste energy as a filament does which has to be first heated until white hot to emit light.
Low Voltage
LEDs can operate from as little as 5 volts but can easily be configured to work from a wide range of voltages to suit specific designs or available power supplies.
No Colour Fade
An LED is designed to emit a specific wavelength of light. This is defined in the LED manufacturing process, they do not rely on colored filters or gels to produce a specific color which could fade over time.
Fit and Forget
LED’s are low maintenance devices and require no servicing during their life.
Simple Installation
LED’s don’t require any special driver circuits, starters, chokes or inverters to operate. They are fully dimmable and can be controlled with simple electronics.
Wide Range of Colors
The basic LED colors are red, orange, amber, yellow, green, blue and white. Within each colour we can offer a range of shades.
Slimline Design
LEDs are physically smaller than many traditional light sources and allow unobtrusive slimline designs to be made.
Sealed Units
LEDs do not need to be changed as with fluorescent or filament bulbs so there is no need for a bulb holder / fitting or the need to make the enclosure accessible for changing the bulb. This simplifies product design as the unit can simply be potted in a clear resin to seal the unit. This also makes the unit tamperproof and more vandal resistant.
Basic LED Types
There are four common LED types.
1. The first and most common is the pinned LED. Most popular being 5mm round types. They are constructed from a metal leadframe onto which the light emitting die is placed a body is then moulded around the leadframe forming the completed LED.
Fig08. LED Type 1
There are many variations to choose from for example Diffused which gives a wide angle of light or waterclear which gives a more directional beam. They are good general purpose LED’s suitable for a wide range of applications, easy to use and simple to assemble.
2. The second type is the Surface mount LED. These generally have the smallest body a die chip can be mounted into. They need to be fitted onto a PCB which can either be rigid or flexible. They offer wide view angles of light and are ideal where space is at a premium.
Fig09. LED Type 2
Fig10. LED Type 3
LED Light Strips
The power LED can operate from low voltage DC supplies or they need supply suitable driver modules which operate direct from the AC mains giving a safe easy to use low voltage output to connect the LED to. All you have to do is wire the LED’s together.
Edge Illuminated Signs
3. The third is the Power LED these are high light output LEDs. They will be mounted on some form of heat conductive material which is needed to draw heat away from the LED die. These are the brightest LED’s manufactured and use large die chips or multiple chips placed in a tight cluster to achieve the brightness.
Fig10. LED Type 3
Thought needs to be given when mounting as generally some form of additional heatsink is need to avoid overheating. The power supply driving the LED also needs to be carefully controlled to avoid damage. Applications include direct illumination, and anywhere a very intense lightsource is needed.
4. The fourth type called C.O.B (Chip on Board) uses the LED die bonded directly to a PCB or substrate. It eliminates the need for an LED body or leadframe to soldered to. Once bonded the die is covered in a clear protective resin which sets hard and protects the die from damage. It is very low cost in high volume applications and allows very small and intricate layouts to be produced.
4. The fourth type called C.O.B (Chip on Board) uses the LED die bonded directly to a PCB or substrate. It eliminates the need for an LED body or leadframe to soldered to. Once bonded the die is covered in a clear protective resin which sets hard and protects the die from damage. It is very low cost in high volume applications and allows very small and intricate layouts to be produced.
Fig11. LED Type 4
LED Light Strips
LED Light Strips are ideal building blocks for signs and displays. They consist of a PCB strip which has a number of LEDs soldered to it they incorporate the current limiting needed so can be connected direct to a suitable power supply without any additional circuitry.
Supplied in 300mm lengths and available in a range of different colours, brightness and view angles.
Supplied in 300mm lengths and available in a range of different colours, brightness and view angles.
Fig12. LED Light Strips
They are simple two wire connection and can be daisy chained together to make longer lengths. They need supply suitable low voltage power supplies to operate these strips or they can be tailored on request to operate from any available low voltage supply you may already have installed. They have flexible strips as well as rigid which makes installation around curves and shaped surfaces possible.
Fig13. LED Light Strips
Power LED’sVery high light output LEDs which are designed for illumination applications. They are available in a full range of colours and with different domed lenses attached which change the view angle to create either intense beams of light or wider flood effects.
Fig14. Power Led
The power LED can operate from low voltage DC supplies or they need supply suitable driver modules which operate direct from the AC mains giving a safe easy to use low voltage output to connect the LED to. All you have to do is wire the LED’s together.
Edge Illuminated Signs
Edge illumination modules allow you to create low power, no maintenance, LED signs which will give many years of trouble free service.
Fig15. Sign Led
Using LEDs allow a number of interesting effects to be produced. Signs can be static single colour or using RGB types change colour either fading from one colour to the next or stepping through a range of colours. Flashing on and off or dimming is also possible.
Fig16. Sign Led
LED Backlight
LED backlights are ideal where you need to create a thin evenly illuminated surface of light. Originally developed for the electronics industry as a light source to back illuminate LCD displays, developments in the technology now allow much larger areas to be illuminated. These larger panels can be used as thin lightboxes to illuminate signs, overlays or transparencies.
LED backlights are ideal where you need to create a thin evenly illuminated surface of light. Originally developed for the electronics industry as a light source to back illuminate LCD displays, developments in the technology now allow much larger areas to be illuminated. These larger panels can be used as thin lightboxes to illuminate signs, overlays or transparencies.
Fig17. Backlight Led
The most common type use a clear acrylic sheet of between 3mm and 10mm thickness (the lightguide) which has LED’s mounted along the panel’s edge firing light into the lightguide from the side. The rear of the lightguide is then coated in a reflective material which creates the even surface of light you see.
LED Displays
LED displays are packages of many LEDs arranged in a pattern, the most familiar pattern being the 7-segment displays for showing numbers (digits 0-9). The pictures below illustrate some of the popular designs.
Fig18. LED Displays
