Introduction to LED Lighting

Introduction

LED’s are solid state semiconductor devices. LED illumination is achieved when a semiconductor crystal is excited so that it directly produces visible light in a desired wavelength range (colour). LEDs are small, typically 5mm.

The light from an LED is practically a pure, single colour. A green LED produces green light only, a red LED only red light, and so on. It is the material of the LED chip that determines the colour.

LED’s are driven by direct current, and the amount of current determines the brightness.

The brightness of the LED is proportional to the current flowing through the LED, more current, more light. In order to create a full range of colours including white light, we need to use a selection of different coloured LED’s that can be combined in various proportions to create a wide colour palette.

Image of LED

Diagram of an LED

Features & Benefits of LED

  • LED’s are extremely efficient low energy light sources
  • In 2005 white LED’s had reached outputs of over 30 lumens/Watt and coloured versions 50 lumens/Watt. The light gains continue to grow, doubling about every two years
  • Long operational life of up to 50,000 hours
  • Compact light source, no other lamp possesses such small dimensions for a comparative light output
  • LED’s do not emit ultraviolet (UV) or infrared (IR) radiation. They do not radiate heat in the direction of the illuminated object, they
  • can therefore be used to illuminate materials that fade easily, food, works of art etc.
  • LED’s are durable against impact and vibration LED’s can be dimmed
  • Coloured light can be produced effectively - over 16 million colours

LED Colour Variation

Due to the manufacturing process of LED’s they are graded into ‘Bins’ of like colour temperature. Even within these ‘Bins’ it is impossible to guarantee the colour temperature of the light. This colour variation can be discernable to the human eye and this should be taken into account when designing lighting plans using LED technology.

Common Applications

  • Display lighting - compact displays are possible with low operating temperatures
  • Display case, museum and shop lighting - illumination of sensitive objects at close range with ultraviolet (UV) and infrared (IR) free light
  • Underwater lighting - low voltage supply for safety and low maintenance
  • Outside lighting - coloured effects to enhance outdoor spaces
  • Sign lighting - strips of LED’s can be used to light signage in many different colours
  • Low level lighting - LED luminaires are cool to touch and are therefore suitable for us in domestic situations where children may come into contact with them
  • Architectural detail lighting - LED’s can be used in applications which traditionally used neon or cold cathode

History of LED

1907 - Henry Joseph Round discovered the physical effect of electro-luminescence.

1962 - The first red luminescent diode appears on the market. The industrially produced LED is born.

1970’s - LED’s are available in further colours: green, orange & yellow.

1980’s to early 1990’s - High performance LED’s (LED modules) in red, orange, yellow & green become available.

1995 - The first LED producing white light by luminescence conversion is launched.

1997 - White LED’s become commercially available

What Is "RGB"?

  • RGB stands for red, green and blue. It is a commonly used term to denote a module or luminaire that has the ability to change colour, up to a maximum of 16 million variations depending on the controller
  • Features include colour phasing, switching and static colours

Lumens

The Lumen (lm) is the unit of measurement for the amount of visible light emitted from a source.

On 1st September 2010 the EU legislation came into force that lighting equipment must be labelled in terms of lumens instead of watts.

Here are some examples of how lumen outputs compare to an incandescent lamp

40 Watt Incandescent = 380-460 Lumens
60 Watt Incandescent = 750-850 Lumens
75 Watt Incandescent = 1100-1300 Lumens
100 Watt Incandescent = 1700-1800 Lumens

So as an example if a lamp is 10 Watts and providing 80 Lumens per Watt you would expect this to be as bright as a 60W Incandescent Lamp.