Green Lighting

By Raghavan Sampath, Field Application Engineer, Freescale Semiconductor

Solar-based HBLED Lighting Solutions

Introduction

Over the last fifteen years, energy demand has grown tenfold and the cost of energy has increased four times over. Blackout and brownout conditions have occurred in the United States and other countries and may continue, as energy demand increases and energy generation fails to keep up. According to a recent report from the North American Electric Reliability Corp., electricity demand in the U.S. alone is expected to grow by 141,000 megawatts in the next decade, while only 57,000 megawatts of new resources have been identified. This leaves a shortfall of 84,000 megawatts, an amount equivalent to 160 large power plants.

Making electricity (much of it power lighting applications) creates 37% of all greenhouse gases, according to the United States Energy Information Administration. Hence, we need to start looking at alternative energy resources, such as solar-power, which is a green technology and does not cost as much as hydroelectric, geothermal or nuclear energy generation.

In the 21st century, there are as many as 300 million homes in underdeveloped countries deprived of adequate lighting. The reasons can vary, but may include affordability (the cost is too high), lack of infrastructure and supply and demand mismatches. Many households use homemade kerosene lamps or candles for lighting. These dim, yellow, smoky light sources can be health hazards and are not eco-friendly. In the long run, they are a more expensive light source than bright, 20white, solar-powered high brightness light emitting diodes (HBLEDs).

Table 1 provides a good comparative study.

 

 

Why HBLED for Lighting?

Longer Life

LEDs last longer than any other light source, in excess of ten years in many applications. They contain solid-state technology similar to that used in the latest microprocessors. These solid-state devices have no moving parts, no fragile glass environments, no mercury, no toxic gasses and no filament. There is nothing to break, rupture, shatter, leak or contaminate. Unlike typical conventional light sources, LEDs are not subject to sudden failure or burnout. There is no point in time at which the light source ceases to function. Instead, LEDs gradually degrade in performance over time.

Most LEDs are predicted to deliver an average of 70 percent of initial intensity after 50,000 hours of operation. In an application where the light source would be used for 12 hours per day, 365 days per year, this could result in a system lifetime of over eleven years with only 30% degradation (70% lumen maintenance) from initial luminous output.

 

Reduced Maintenance Costs

Since LED-based light sources last up to ten times longer than a traditional light source, there is no need for frequent replacement, reducing or even eliminating ongoing maintenance costs and periodic re-lamping expenses. This can be particularly important in critical, regulated lighting applications, such as buoys, beacon lights, emergency exit lighting, back up lighting and security lighting that would normally require scheduled, periodic bulb replacement.

 

 

More Energy Efficient

LED light sources are more efficient than incandescent and most halogen light sources. White LEDs today deliver more than 20 lumens per watt and are predicted to achieve greater than 50 lumens per watt in the future. When choosing solid-state lighting as an alternative, it is important to consider the total system level benefits. For example, with superior lumens per watt performance, LEDs used in a building lighting system consume less energy per hour than competing lighting sources, making them more eco-friendly and cost effective.

 

LED Benefits

• Reliable (100K hours) – reduced maintenance costs
• More energy efficient – green, cost effective solution
• Instant on and fully dimmable without color variation – pulse width modulation (PWM) control
• No mercury – conforms with environmental regulations
• Low voltage DC operation – eliminates high voltage connections

 

 

How Solar-Powered LED Lighting Works

Above is a block diagram that illustrates solar-based LED lighting implementation

A solar panel converts solar energy to electric voltage, which is stored in a battery. Freescale’s 8-bit HCS08QG4/8 microcontroller (MCU), with a 2-channel, 16-bit timer, is used for battery charging and monitoring and to drive the LEDs. PWM is used for battery charging and an analog-to-digital converter (ADD) is used for monitoring the battery voltage. If that voltage falls below 50% of a full charge, the LED’s brightness is automatically reduced to 50% by varying the duty cycle of the second PWM channel. The idea is to provide light for longer durations, even at lesser brightness. If the battery voltage drops to 10%, then the MCU turns the LED off to ensure the battery is not completely drained.

 

Choosing the Right Microcontroller

Multiple alternatives exist in selecting an MCU for the solar-powered LED application; the HCS08QG4/8 device offers an excellent combination of the features needed at a very competitive cost.

The MC9S08QG8/4 extends the advantages of Freescale’s HCS08 core to low pin count and small package options. QG devices are low voltage, with on-chip in-circuit Flash memory programmable down to 1.8V. They include the standard features of all HCS08 MCUs, including wait mode and multiple stop modes, strong analog capabilities, a complete set of serial modules, a temperature sensor and robust memory options.

 

 

Applications

Solar-powered HBLED lighting for street lights, home lighting, emergency lights and rural lighting

Traffic lights are operational for the entire day in most cities and street lights for much of the day. Substituting HBLED technology for the traditional halogen or compact fluorescent lamp (CFL) solutions can provide enormous savings in terms of reduced energy consumption and lower maintenance costs.

The International Finance Corporation (IFC), the private sector investment arm of the World Bank Group’s "Lighting the Bottom of the Pyramid" project plans to sell solar-powered LED lighting systems to the 1.6 billion people around the world that are not connected to the electrical grid. Lacking access to electrical lighting, many of these people and their businesses instead rely on carbon fuels, such as kerosene for their lighting needs. By using solar energy and LED lighting in these locations, health hazards can be reduced, as well as greenhouse gas emissions associated with the burning of fossil fuels.

 

 

One Last Note on Energy Savings

In 2006, China was the world’s second largest electricity consumer, generating 2,475 billion kWh. 12% of that went into lighting. By 2020, if LED efficiency reaches 150lm/W and penetrates just 30% of the Chinese market, the energy savings could reach 200 billion kWh per year.

 

Conclusion

LED lighting technology is a significant, quantifiable, energy and cost reducing lighting alternative that provides low maintenance solutions for a wide variety of lighting applications. By using significantly less electricity than more traditional lighting methods, LEDs also help the environment by cutting electric power generation and its associated greenhouse gas emissions.

 

Raghavan Sampath graduated from Bangalore University in 2000 with a Bachelor of Engineering in Electronics and Communication. He has been with Freescale Semiconductor for almost two years. He is a Field Application Engineer.