**1. Introduction**

The manufacturing industry is pushing a technological evolution toward the general adoption of the increasingly extended digital systems. This process has been observed in cameras, televisions, automotive controlling, telephones, and, lately, in lighting products with the introduction of LEDs as effective light sources.

> © 2016 The Author(s). Licensee InTech. This chapter is distributed under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/by/3.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited. © 2018 The Author(s). Licensee IntechOpen. This chapter is distributed under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/by/3.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.

In this last sector, this new nature implies bigger energy efficiencies (which make a major contribution to sustainability as, approximately, 20% of the total energy consumed in the world is used for indoor and outdoor illumination [1]) and robustness and easiness of control (allowing brightness regulation, status supervision, or even the generation of a proprietary data transmission network [2]). However, minimizing energy usage within this new trend goes far beyond the light source and the saving that can be achieved through occupancy sensing and dimming. It also brings a new way or energy use: the opportunity for better efficiency also extends to their power grid.

1883 the first technically usable transformer which made possible to step up and down easily

DC Network Indoor and Outdoor LED Lighting http://dx.doi.org/10.5772/intechopen.74974 17

As DC electricity was not converted efficiently into high voltages until the 1960s, a DC power network implied the installation of small/medium power plants in every block of a city (which reduces the efficiency of the system), and, besides, Nikola Tesla presented in 1888 the first AC

More than 120 years later, AC still constitutes the basis of our power infrastructure. However, two converging factors have renewed the interest in DC power consumption grids in this last

• There are better alternatives for decentralized power generation, PV panels being its most significant technology. They produce DC power and so do chemical batteries, which are

• Most of our electrical appliances operate internally on DC power. AC electricity is trans-

Within the next 15 years, more than half of the total household loads are expected to run

LEDs are an "old" technology that, in recent years, is undergoing numerous advances and transformations toward new applications that are leading the latest revolution in the lighting

The first fully electronic-type light source consists of a semiconductor diode base on the junction of two segments of a crystal. When a differential voltage is applied on both extremes of the diode—direct way polarization—it generates photons with an electromagnetic radiation of a specific frequency related by the Planck constant. This allows efficient monochromatic light generation if the frequency emitted is within the range of the human eye vision (~400–700 nm). The research on dopants and crystal structures has led to more efficient and higher-power LEDs. However, white-light sources have been possible through a long path of

At the end of the 1990s, the blue LED became a reality developed by Isamu Akasaki and Hiroshi Amano (Nagoya University) and Shuji Nakamura (Nichia Corp). They were awarded with the Nobel Prize in physics in 2014 for this work. They were looking for a precise tool to improve optic data storage systems but they also achieved the basic principle of the latest breakthrough in LED technology: a very efficient and stable white-light emission using phosphorus, not as a dopant, but as a coating for the silicon crystal of blue LEDs and, consequently, to be able to use these devices as sources in general lighting applications as substi-

Mass-produced LEDs are reaching rapidly comparable results to prototypes being developed in research laboratories, and the electronic drivers that operate LED lamps are also constantly improving on efficiency and robustness. Present projections are contingent on technology

developments that achieve the goal of 200 lm/W luminaire efficacy by 2025 [7].

the AC voltage to carry power over long distances from a power plant.

engine, eliminating the other greatest argument for building up DC grids.

the most practical storage technology for PV systems [4].

development generated aside this type of semiconductor.

tutes of fluorescent bulbs and discharge lamps (see **Figure 1**).

formed into DC with specific nonefficient internal converters.

directly on DC, and LED lights are one of the main actors of this trend [5].

decade:

**1.2. LED technology**

industry [6].

As LEDs work naturally on direct current (DC), drivers are a basic requirement for any lighting equipment powered with the common alternate current (AC) power network of public lighting and buildings. The movement toward a new DC grid allows to enhance the characteristics of LED luminaires: better global efficiencies (minimizing power conversions) and reliability (AC/DC systems have a natural lifetime expectation significantly lower than the LEDs, and they are the most common point of failure in AC luminaires), simplifies household equipment (eliminating many small power supplies), and may obtain better security conditions as very low voltage distribution (VLDC <75 VDC European Council Directive 73/23/EEC) may be possible in many cases. Moreover, advance lighting controls are being developed that are fully integrated inside these DC systems at no higher cost [3].

Until recently, DC LED lights were designed exclusively to be used with battery-based offgrid power sources. However, DC grids have been investigated more intensely in the last decade since many renewable energy sources as well as electronic and control technologies are being developed.

Modern energy consumption grids are thought to be powered in DC either by renewable energy—mainly photovoltaic (PV) panels—centralized AC/DC conversion units, energy storage systems—bank of batteries, electric cars (V2G), and so on—or a combination of all of them.

In this chapter, we analyze the evolution and present developments of new DC energy consumption grids and how LED control technologies are evolving to adapt themselves to these new powering models. Lately, we expose, analyze, and discuss several significant initiatives and projects developed for both indoor and outdoor related to DC LED lighting.

### **1.1. DC grids**

The world runs on AC since electrical power transmission was introduced in the last quarter of the nineteenth century, and AC and DC competed to become the standard power distribution system in the process known as the "War of the Currents."

The light bulb, incorporating a high-resistance carbon filament, was industrially developed in the last quarter of the eighteenth century. Thomas Alva Edison was developing an industry to manufacture these bulbs but also to provide a complete infrastructure of power plants, transportation grids, and end-use devices such as fuses and switches. Edison opted for DC to share the same grid that was used to power electric engines, which ran this way at the time.

However, George Westinghouse (Westinghouse Electric Corporation) focused on the limited range of the low-voltage DC. At a time when power electronics were too limited, he found in 1883 the first technically usable transformer which made possible to step up and down easily the AC voltage to carry power over long distances from a power plant.

As DC electricity was not converted efficiently into high voltages until the 1960s, a DC power network implied the installation of small/medium power plants in every block of a city (which reduces the efficiency of the system), and, besides, Nikola Tesla presented in 1888 the first AC engine, eliminating the other greatest argument for building up DC grids.

More than 120 years later, AC still constitutes the basis of our power infrastructure. However, two converging factors have renewed the interest in DC power consumption grids in this last decade:


Within the next 15 years, more than half of the total household loads are expected to run directly on DC, and LED lights are one of the main actors of this trend [5].

### **1.2. LED technology**

In this last sector, this new nature implies bigger energy efficiencies (which make a major contribution to sustainability as, approximately, 20% of the total energy consumed in the world is used for indoor and outdoor illumination [1]) and robustness and easiness of control (allowing brightness regulation, status supervision, or even the generation of a proprietary data transmission network [2]). However, minimizing energy usage within this new trend goes far beyond the light source and the saving that can be achieved through occupancy sensing and dimming. It also brings a new way or energy use: the opportunity for better efficiency

16 Light-Emitting Diode - An Outlook On the Empirical Features and Its Recent Technological Advancements

As LEDs work naturally on direct current (DC), drivers are a basic requirement for any lighting equipment powered with the common alternate current (AC) power network of public lighting and buildings. The movement toward a new DC grid allows to enhance the characteristics of LED luminaires: better global efficiencies (minimizing power conversions) and reliability (AC/DC systems have a natural lifetime expectation significantly lower than the LEDs, and they are the most common point of failure in AC luminaires), simplifies household equipment (eliminating many small power supplies), and may obtain better security conditions as very low voltage distribution (VLDC <75 VDC European Council Directive 73/23/EEC) may be possible in many cases. Moreover, advance lighting controls are being developed that

Until recently, DC LED lights were designed exclusively to be used with battery-based offgrid power sources. However, DC grids have been investigated more intensely in the last decade since many renewable energy sources as well as electronic and control technologies

Modern energy consumption grids are thought to be powered in DC either by renewable energy—mainly photovoltaic (PV) panels—centralized AC/DC conversion units, energy storage systems—bank of batteries, electric cars (V2G), and so on—or a combination of all of them. In this chapter, we analyze the evolution and present developments of new DC energy consumption grids and how LED control technologies are evolving to adapt themselves to these new powering models. Lately, we expose, analyze, and discuss several significant initiatives

The world runs on AC since electrical power transmission was introduced in the last quarter of the nineteenth century, and AC and DC competed to become the standard power distribu-

The light bulb, incorporating a high-resistance carbon filament, was industrially developed in the last quarter of the eighteenth century. Thomas Alva Edison was developing an industry to manufacture these bulbs but also to provide a complete infrastructure of power plants, transportation grids, and end-use devices such as fuses and switches. Edison opted for DC to share the same grid that was used to power electric engines, which ran this way

However, George Westinghouse (Westinghouse Electric Corporation) focused on the limited range of the low-voltage DC. At a time when power electronics were too limited, he found in

and projects developed for both indoor and outdoor related to DC LED lighting.

tion system in the process known as the "War of the Currents."

are fully integrated inside these DC systems at no higher cost [3].

also extends to their power grid.

are being developed.

**1.1. DC grids**

at the time.

LEDs are an "old" technology that, in recent years, is undergoing numerous advances and transformations toward new applications that are leading the latest revolution in the lighting industry [6].

The first fully electronic-type light source consists of a semiconductor diode base on the junction of two segments of a crystal. When a differential voltage is applied on both extremes of the diode—direct way polarization—it generates photons with an electromagnetic radiation of a specific frequency related by the Planck constant. This allows efficient monochromatic light generation if the frequency emitted is within the range of the human eye vision (~400–700 nm). The research on dopants and crystal structures has led to more efficient and higher-power LEDs. However, white-light sources have been possible through a long path of development generated aside this type of semiconductor.

At the end of the 1990s, the blue LED became a reality developed by Isamu Akasaki and Hiroshi Amano (Nagoya University) and Shuji Nakamura (Nichia Corp). They were awarded with the Nobel Prize in physics in 2014 for this work. They were looking for a precise tool to improve optic data storage systems but they also achieved the basic principle of the latest breakthrough in LED technology: a very efficient and stable white-light emission using phosphorus, not as a dopant, but as a coating for the silicon crystal of blue LEDs and, consequently, to be able to use these devices as sources in general lighting applications as substitutes of fluorescent bulbs and discharge lamps (see **Figure 1**).

Mass-produced LEDs are reaching rapidly comparable results to prototypes being developed in research laboratories, and the electronic drivers that operate LED lamps are also constantly improving on efficiency and robustness. Present projections are contingent on technology developments that achieve the goal of 200 lm/W luminaire efficacy by 2025 [7].

Given a constant "Tj," the illuminance of HP LED varies linearly with its "If" at small values and tends to saturate at higher values. Otherwise, if a constant current (CC) drive is forced, the light emitted moves down as "Tj" increases. This is caused by the variation relationship between "Vf" and "Tj," which is approximately proportional [8]. For the XT-E LED by CREE, the typical relationship is −2.5 mV/°C. This effect makes itself visible in the displacement of its working curves. These "Vf"-"If"-"Tj"-"Luminous flux" relationship curves of the mentioned LED are shown in **Figure 2**. Consequently, if a CC is applied on the LED, the increase in the junction temperature causes only a slight decrease in its "Vf" drop and, at the same time, in the illumination obtained, creating a natural mechanism of negative feedback that maintains the stability of the system. However, if we use a constant "Vf" with LEDs, its power consumption increases along with its "Tj," produced by a significant increment in the forward current, creating a positive feedback that will finally conduct to a catastrophic burn failure. This phenomenon is generally known as thermal runaway and is the reason why the standard method of driving LEDs is the use for

DC Network Indoor and Outdoor LED Lighting http://dx.doi.org/10.5772/intechopen.74974 19

Because of this electrical behavior of HP LEDs, in case of DC supply, we need to have a current control device in series with the LEDs to guarantee stable working conditions. Creating a regulated current source can go from a very simple concept, using a passive polarization resistor, to a more complex solution using active current regulator circuits. Here, we summarize the general trends found in the study and the market to achieve this objective, accounting

The simplest driver is a current-limiting resistor placed along with the powered LEDs. The reduction in the polarization voltage of LEDs due to temperature increment is compensated with the larger drop in the resistor (negative feedback effect). If the supply voltage is very well defined and stable, close to "Vf," this is the simplest, most reliable, and long-lasting LED driver. However, it is not significantly efficient as all the required current is driven through these impedances generating a significant amount of heat, and a substantial resistance value is required to keep current within an adequate range. If the voltage source is not stable, the brightness of the LED would vary remarkably because a small voltage variation would already lead to large changes of the output power. This system is only able to correct the

Active current control uses bipolar or MOSFET transistors as regulation devices or feedback elements to regulate the current driven through the LEDs. In contrast to the polarization resistors,

nonsteady (batteries) and steady (switching converter outputs) DC sources.

variations of the behavior of the LED due to the changes of its "Tj."

**3.1. Passive control methods: polarization resistors**

DC current sources.

**3. DC LED drivers**

**3.2. Active control methods**

*3.2.1. Linear power drivers*

**Figure 1.** High power 3000 K white XTE LED by CREE. Blue emitter with phosphorus cover.
