Light Emitting Diodes

Incandescent Bulbs

100-year-old Inefficient Light Technology

Incandescent bulbs use a 100-year-old technology that generates light by passing a large amount of electrical current through a small wire. This wire glows white-hot (almost) and radiates energy in all directions. A consequence of this method of generating light is that only 15% of the energy produced is visible light; the remaining 85% is dissipated as heat!

Out of the rainbow of colors that make up white light, you have to filter out all of the light, except the color you want the lantern to emit (i.e., a blue lens blocks or filters out all light except blue). In the end, very little of the energy emitted by the incandescent lamp is seen by the observer through the colored filter.

As illustrated above, for filtered interior incandescent bulbs, the intensity depends on the color. For blue, the filtered transmission is about 0.4%, for green, about 1%, and for red, about 1.5%. The rest of the energy is wasted in heat dissipation.

Compact Fluorescent Lamps

Convenient, but Fragile, Complex and Environmentally Hazardous

Compact fluorescent lamps (CFLs) were developed as a relatively efficient alternative to incandescent bulbs and many solar-powered outdoor lighting products utilize these lamps as their light source.

In short, fluorescent lamp technology consists of a thin glass tube filled with argon/mercury vapor. At each end of the tube are metal electrodes coated with an alkaline-earth oxide that gives off electrons easily. When a current is passed through the ionized gas between the electrodes, the fluorescent lamp emits ultraviolet radiation. The inside surface of the fluorescent tube is coated with phosphors, typically zinc silicate or magnesium tungstate. These phosphors absorb the ultraviolet radiation and re-radiate the energy as visible light. A fluorescent lamp will operate until the alkaline-earth oxide coating on its electrodes is depleted.

When starting a fluorescent lamp, the unit requires a "boost" in the form of a starter and ballast that provide up to four times the operating voltage in the beginning.

Disadvantages of CFLs:

• High energy consumption. CFLs can consume up to 20 watts, depending on their application (although the tubes are listed at a lower wattage, it is important to consider that the driving ballasts use energy as well). This level of power consumption requires large, expensive solar modules and associated installation hardware to generate the required energy. In addition, large batteries are required for power storage and typical reserves are less than a week - this doesn't leave enough autonomy to compensate for seasonal or poor climatic conditions.

• Difficult to power manage. CFLs tend to be either "on" or quot;off". Although it is not impossible to adjust the output dynamically, it is a complicated process. This makes power management difficult, imprecise, or non-existant, which is a liability for solar-powered lighting products where the source of power varies according to seasonal fluctuations and prevailing weather conditions.

• Short operational life. The rated life of typical CFLs is about a year and products using them require regular maintenance. This increases the life cycle cost of the product in terms of servicing labor, storage costs and proper disposal (fluorescent tubes and their ballasts are considered hazardous materials).

• Temperature degradation. Manufacturers of CFLs conduct their rated life and light output calculations under ideal operating conditions and temperatures that usually do not reflect the actual environmental conditions. The performance and lifespan of CFLs is dramatically degraded by extremes in ambient temperature.

• Fragility. Another drawback with CFLs is that they are composed of fragile glass tubing. If the fixture is impacted with minimal force, the tube will break and the lamp will cease to operate. Moreover, the resulting glass fragments are sharp and dangerous.

• Hazardous materials.The EPA in the United States regulates the disposal of CFLs because of they contain highly toxic mercury. The ballasts are also regulated under the Toxic Substance Control Act (TSCA) and Comprehensive Environmental Response Compensation and Liability Act (CERCLA) because they contain PCB's and other toxic components.

LEDs

Efficient, State-of-the-Art Light Technology

At the heart of a Light Emitting Diode (LED) lamp is a silicon "chip" about the size of a grain of salt and made of a special blend of crystals. When a small electrical current is passed through the chip it generates light.

LEDs offer a number of technical advantages over any other type of lighting, including:

• Unlike incandescent bulbs or even fluorescent lamps, almost all of the energy used by LEDs is converted to light, rather than heat.

  

  As the examples in the graph above indicate, the luminous efficiency for an LED ranges from about 5% for blue to just over 20% for red, and almost no energy is wasted through heat dissipation.

• Furthermore, the shape of the LED package focuses the light without the need for additional optical components, making them more efficient and cost-effective at utilizing the light produced. The isotropic nature of incandescent or fluorescent lamps requires external optics to collect the emitted light and direct it in a usable fashion.

• The combination of these effects makes LEDs many times more efficient at producing light than incandescent bulbs or fluorescent lamps. In addition, the lifetime of an LED is about 100,000 hours (27 years assuming the LED is on continuously for 10 hours per day); this is about 20 times as long as the best incandescent bulbs (5,000 hours) and twice as long as the best fluorescent lamps (cold cathode CFLs are rated at about 50,000 hours).

• LEDs are extremely durable. Vibration or shock easily breaks the fragile filament in an incandescent bulb and the glass tubing of a fluorescent lamp. LEDs, on the other hand, are completely solid-state technology and are virtually indestructible!

Solar Power Systems

A Brief Introduction to Solar Power

Solar panels, also called "photovoltaic" (photo = light, voltaic = electricity) modules are comprised of a group of photovoltaic cells connected together in a single frame. These cells are made of special semiconductive materials, the most common of which is silicon. Typically, these silicon cells are manufactured in 6-inch disks that produce approximately 1/2 volt per cell. These disks are then cut into 4-inch squares (and for our applications are cut into still smaller strips) and strung together in series to generate the required voltage for our products.

When the photons of sunlight strike each photovoltaic cell, a certain portion of them are absorbed into the silicon; in other words, the energy of the sun is transferred to the semiconductor. This energy releases electrons in the semiconductor, enabling them to flow freely. All solar cells have one or more electric fields that force these freed electrons to flow in a certain direction, which is called a current. When metal contacts are attached on the top and bottom of each photovoltaic cell, this current can be drawn off for external use. When combined with each cell's voltage, the current defines the power (in Watts) that the photovoltaic cells can produce.

Photovoltaic cell technology has progressed significantly in recent years. Cost reductions, improved energy efficiency (the ability of the cells to transform sunlight into usable energy) and higher production rates mean solar power is now available for an increasing number of applications - from solar calculators to large solar power stations.

A Comparison of Solar Panels

Not all solar panels are created equal! There are large variations in durability, performance and price. The solar panel used by a manufacturer defines the capabilities, reliability and physical appearance of a solar-powered product. However, there is a fine balance as solar panels providing only slightly more charging power often show a significant increase in price - resulting in solar-powered product too expensive for market expectations.

Carmanah's Solar Power Systems

Carmanah performed a great deal of research prior to selecting the solar panels used in all of its products. The company's efforts were focused on maximizing the durability, quality and performance of its solar power systems while minimizing cost, thus ensuring it has superior reliable products that are priced competitively with other solar and even non-solar alternatives.

Carmanah chose a monocrystalline solar panel technology as the basis of its solar power systems. Originally designed for the U.S. armed forces, this technology has been thoroughly tested under extreme environmental conditions and is more efficient (up to 14%) than the polycrystalline or amorphous (6-7%) solar panel technologies typically used in consumer grade solar-powered products. Carmanah's solar panels are also custom-made to match the specifications of the battery system used in each of its products.

Carmanah's Proprietary Solar Panel Dome

Carmanah manufactures its products with a solar panel fully encapsulated in a patented polymer dome design. This dome provides a number of benefits:

• With Carmanah's proprietary dome design, the solar panel does not have to meet these installation requirements in order to draw the energy it needs for charging.

• As the solar panel is sealed in the polymer, it is very well protected. The polymer is extremely shock resistant, UV resistant, and will not crack or fade in the sun. The solar panel is therefore much more durable than those used in other solar products (commercial or consumer), and can take a great deal of abuse.

• The shape of the solar dome is a deterrent to birds, as they find it more difficult to stand on the dome than on lights with flatter surfaces. In addition, the polymer used is non-porous, very smooth and self-cleaning. It either eliminates the need for cleaning or extends the interval between cleanings significantly.

• The shape of the solar dome eliminates the need for a bird spike, which would cast a shadow and deteriorate the solar panels ability to function.

• The overall benefit, of course, is that Carmanah's products can be used in far more applications than typical solar-powered products and require no real technical knowledge of solar power for proper installation.

Carmanah's Solar Powering Process

As explained above, the solar panels used by Carmanah collect light energy from the sun and convert it to electrical current, which in turn creates power which is stored by the product's battery system.

How quickly the solar panels will recharge the battery system is affected by:

Power Storage

Carmanah has chosen to use a lead-acid technology, specifically a pure lead-tin acid electrochemistry utilizing a patented starved electrolyte. Through careful consideration of the worldwide use of its products, Carmanah has chosen to use this battery technology for a number of compelling reasons:

Performance Benefits of Pure Lead-Tin Acid Batteries

• The pure lead-tin acid batteries used by Carmanah have been specifically designed to survive in harsh outdoor environments. NiCd and NiMH batteries were never intended for outdoor use. In fact, NiCd batteries have almost no recharging ability below the freezing point (0°C, 32°F) and NiMH are not much better (-10°C, 14°F).

• A pure lead-tin grid inhibits corrosion and acid vapor venting. Combine this with its low internal resistance, and the battery is able to provide longer service life under a wider range of conditions than any other battery of comparable size.

• Unlike NiCd or NiMH batteries, pure lead-tin acid batteries offer a long shelf life - up to 2 years at 25°C (77°F).

• Carmanah's electronics make every attempt to charge their batteries with a constant voltage, however when solar conditions are not adequate for this process, the pure lead-tin acid batteries will tolerate trickle charging much better than NiCd or NiMH.

• It is also important to note that while some other lead-acid technologies may experience freezing problems at low temperatures when they are greater than 50% discharged, tests show the pure lead-tin acid technology utilized by Carmanah is not affected in the same way.

• Pure lead-tin batteries have a much longer operating life that NiCd or NiMH batteries. In fact, pure lead acid batteries are rated to last three times as long as NiCad and twice as long as NiMH. In addition, pure lead batteries do not develop a memory like both NiCd and NiMH. Although all batteries are impacted by high temperatures, the lifespans of NiCd and NiMH are also more dramatically reduced as temperatures increase.

Carmanah Battery System Enhancements

Carmanah's lighting products have been further engineered to improve the performance and endurance of its pure lead-tin battery systems. Key enhancements include:

2. Carmanah has properly matched the configuration of its batteries to meet each product's unique powering requirements. The systems are designed so that they never discharge beyond 80% depth of discharge. In fact, typical discharges are maintained in a range of 25% depth of discharge or less.

3. Carmanah's products incorporate a low voltage cutoff to prevent over-discharge of the battery system.

Environmental Benefits of Lead-Acid Batteries

Lead-acid batteries are the environmental success story of our time. Approximately 93 percent of all battery lead is recycled - compared to 59% of newspapers, 65% of aluminum soft drink and beer cans, and 40% of plastic and glass soft drink bottles. In fact, lead-acid batteries top the list as the most highly recycled consumer product in the world today.

Due to their widespread use in the transportation industry and strict legislation, lead-acid batteries have huge, successful recycling programs in all advanced countries. Nearly every town has a lead-acid battery recycling facility that accepts old batteries at no cost. The lead-acid battery gains its environmental edge from its closed loop lifecycle. The typical new lead-acid battery contains 60 to 80 percent recycled lead and plastic. When a spent battery is collected, it is sent to a permitted recycler where, under strict environmental regulations, the lead and plastic are reclaimed and sent to a new battery manufacturer. The recycling cycle goes on indefinitely. That means the lead and plastic in the lead-acid battery have been - and will continue to be -- recycled many, many times.

The Environmental Disadvantages of NiCd and NiMH Batteries

Nickel Cadmium

Although both Lead and Cadmium are toxic, Cadmium is also carcinogenic. In fact, there have been strong movements to have NiCd batteries banned entirely in the EU and the nordic countries. Through political lobbying, manufacturers have fought back with the promise of setting up recycling arrangements. So far, these recycling efforts are in their early stages and have been largely unsuccessful.

The NiCd battery is one of the more hazardous batteries in terms of disposal. Cadmium can accumulate in the environment by leaching into ground water and surface water from landfills, and it can enter the atmosphere through incinerator smokestack emissions. Effective air pollution control equipment at incinerators traps cadmium, which ends up in the ash, causing problems of cadmium in ashfill leachate. Our oceans are already beginning to show new traces of cadmium. Cadmium is toxic to fish and wildlife and can pass to humans through the food chain. It has been associated with numerous human illnesses particularly lung and kidney damage. Once absorbed in the body, cadmium can remain for decades.

Nickel Metal Hydride

Although NiMH batteries are considered a more "environmentally friendly" technology than both NiCd and lead-acid, the main derivative is nickel - which is considered semi-toxic. NiMH also contains an electrolyte that, in large amounts, is hazardous to the environment. NiMH battery recycling programs are nowhere near as widespread or as successful as lead-acid battery recycling programs; therefore, in practise, most NiMH batteries are disposed of in local landfills.

So... Why Would Some Manufacturers Still Choose to Use NiCd or NiMH Batteries?

NiCd and NiMH technologies are still selected by many manufacturers because they are readily available, relatively cheap and very compact/lightweight compared with lead-acid. However, it is Carmanah's belief that the overall long-term performance of products using these technologies is in jeapardy. Adequate consideration has not been given to the range of environmental conditions in the world today and the effects these conditions will have on their battery systems. Carmanah's lighting products are typically used in areas where reliability is the primary concern, and the extra cost and weight of using the right battery technology far outweighs the disadvantages.

Automatic Light Control

The Historical Problem with Solar-Powered Lighting

The single greatest inefficiency of outdoor solar-powered lighting products is that they must be optimized for the worst solar conditions that they are likely to encounter. In practical terms, this means that each unit must be designed to operate reliably during the worst of the winter months, when the availability of ambient light for recharging is at its lowest. The result is that during summer months the unit is "overbuilt" and operating inefficiently, as it is unable to use much of the energy available for capture by its solar panels.

Similarly, unless each unit is customized individually, there is no means of adjusting the performance level of a unit to correlate with the solar energy available at the installation location. For example, a unit installed in Egypt, where there are six hours of sunlight on average every day, will have to be set to the same performance level as a unit installed in Patagonia, where there is only one hour of sunlight available on average. The unit in Egypt therefore operates very inefficiently, as most of its incoming solar energy is wasted.

Carmanah's Ingenious Solution

Using advanced electronics and software developed by Carmanah, ALC enables Carmanah's products to automatically adjust their light output in response to prevailing solar conditions.

ALC uses a control scheme to monitor the charge received by its batteries over the course of the day via the solar panel(s). Through a sophisticated algorithm, ALC recognizes any trend in its battery voltage levels to develop an approximate understanding of its installation location and/or prevailing weather conditions. It then determines if solar conditions are suitable to maintain its current light output, or if it should dynamically adjust its output level to ensure its battery levels will remain optimal for continuous, reliable operation. This self-configuring capability enables Carmanah's products to operate reliably at nearly any location on earth. Carmanah currently has more than 90,000 units operating in 110 countries with some units operating year round as far as 70°N latitude (ie. Norway).

The resulting benefits of ALC are significant for Carmanah's customers:

Power Management

The MicroSource™ Power Management system uses a two stage charging process:

Independent Light Output

As batteries discharge over the course of the night, many battery powered lighting products become dimmer and dimmer. To avoid this characteristic, Carmanah has developed low voltage LED driver electronics that are custom designed for each product and ensure that the LEDs receive a constant drive level - independent of the state of the battery system.

These drivers are sophisticated and feature a number of innovative enhancements:

• Precise brightness control and power consumption adjustment is achieved by pulse width modulation. In simple terms, this means to achieve an equivalent of 50% brightness, the LEDs are pulsed so that they are operating only 50% of the time. The rate of modulation is fast enough that it is not detected by the human eye. Pulse with modulation enables the brightness to be adjusted while maintaining the LEDs at their highest power efficiency. Unlike conventional filament bulbs, pulsing also has no detrimental affect on LED lifespan.