SOLID STATE LIGHTING (SSL). Cécile Rosset MSc. Environmental Engineering Technische Universität München. 1 Introduction. History of Lighting. 3 traditional Technologies: Fire Incandescence. Fluorescence & High Intensity discharge. Incandescent bulbs.
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MSc. Environmental Engineering
Technische Universität München
SSL: Creation of first light emitting diodes (LED)
At that time, LEDs were used for showing the time in an alarm clock or as a battery indicator
corresponds to 19% of the worldwide energy consumption.
Reducing energy consumption
by using LEDs will significantly
reduce the level of
CO2 emissions, therefore positively
impacting climate change1 Introduction
World Lighting Pollution
(Blue and white are much harder to obtain)
For a long time unavailable; relied on blue coating!
An ultraviolet GaN LED
BUT: Poor efficiency!
By juxtaposing at a certain distance blue, red, and green LEDs, white light was obtained.
Most simple method but not often used nowadays.
CIE diagram of human vision
maximizes light emission and minimizes turn-on voltage and series resistance
Because most of the light generated at the junction escapes the device through the top surface
the large-area p-contact has to be made as transparent as possible outside the area where electrical bond wires are attached
the internal QE of double heterostructure can be greater than 99%
Double Heterostructure: change in bandgap
The present state-of-the-art is 30% external efficiency in AlGaAs-based LEDs, employing a thick transparent semiconductor superstrate, and total substrate etching in a particularly low-loss optical design.
Efficiency of 43% attained with an efficient NUV LED. The device structure consists of an MQW on a lateral epitaxy on a patterned surface and is flip-chip mounted on a silicon substrate.
Tunability of the final emission spectrum, by controlling the particle size distribution and/or surface chemistry thus white light colour is better
quantum efficiency of 76% (in solution) for a blue emission, in GAN led
These are LEDs whose emissive electroluminescent layer is composed of an organic compound or polymer that will luminesce blue, green and red, and are covered with a transluscent material.
Advantages: -more easily integrated with other electronic components -it can emit white light intrinsically
Problems: degradation in air & easily damaged by exposure to water
BUT: Better efficiency and longer lifetime
Figure 1. LED vs. conventional light sources degradation in light output over time
runway in airports
Incandescent traffic lights replaced by LEDs in USA:
2.5 billion kWhours
= US$ 200 million
= 3 billion kilos of CO2 released in the atmosphere
Solid material that is between insulators and conductor:
Behaves like an Insulator (large bandgap) at room temperature
Behaveslike conductor (no bandgap) when applying electric field
Luminescence2 LED Mechanism
The maximum junction temperature is , but the aim is to keep low
a4 Towards a better efficiency
R1 + R2
R1 + Rh + R2