Technical Information

Contents

1. Lighting Systems

While the users sit paramount in our minds, technology is an unavoidable factor in the implementation of our business models. The following section provides a brief overview of different kinds of lighting systems along with a brief discussion of possible design considerations.

* Average amount spent on kerosene in India ($0.40 due to government subsidy that is being phased out in the coming years), China ($1.50) and Mexico ($1.60). Numbers for China were used because the India subsidy will disappear in coming years and the monthly cost of kerosene in Mexico is higher than that of China.

** This figure is much higher in reality due to the great unreliability (especially in the third world) and general fragility of incandescents.

Assumptions Made to Generate Numbers in Chart

• Batteries need to be recharged once a week for an LED lighting system
• Batteries are similar to the Lead Acid batteries found on motorcycles (Lead Acid batteries were chosen for this chart because they are currently in use by LUTW)
• Lead Acid batteries need replacing every four years
• All lighting systems have equal maintenance and repair costs
• Battery costs $14.00 (retail motorcycle battery costs ~$40)
• Raw data is primarily from India, data assumed applicable to China and Mexico
• Kerosene numbers are generated from the simple wick-type Kerosene lighting system
• Charging station
  • Initial cost of $20 to be paid back in 6 months while charging 25 units 4 times a month for an LED lighting system for $0.03 a charge

1.1 Overview of Lighting Systems

Electricity-Based Systems

• LED
  • Solid state (nearly indestructible)
  • Produces non-directed light from a point source allowing for efficient light concentrating reflectors
  • Long life
  • Runs on low voltage (2.5 - 3 V)
  • Only 80% of the voltage from the power source can be dropped over the LED array to ensure constant illumination
  • Expensive compared to incandescent
• Fluorescent
  • Cheap
  • Relatively energy efficient
  • Produces non-directed light
  • Fragile
  • Restricted minimum output
  • Under decreased voltage conditions light does not function at all instead of dimming as an incandescent does.
  • Difficult to make unit small due to ballast
  • Run on AC current (large disadvantage in terms of complexity)
• Incandescent
  • Inexpensive
  • Easily obtainable
  • Produces non-directed light
  • Extremely fragile
  • Inefficient
• All Electrical Units
  • No fumes produced at point of use
  • Non portable given assumed motorcycle battery
  • For off-grid areas requires new forms of infrastructure and induces new ways of life
  • High initial investment

Chemical Fuel Systems

• Kerosene
  • Portable
  • Relatively expensive
  • Existing infrastructure already exists
  • Diffuse orange light
  • Mild heath hazard
  • Fire hazard
  • Unpleasant to use by United States standards
  • Difficult to mount light reflecting / collecting hardware due to flame characteristics
  • Current distribution methods cause hardship to users

2. Design Considerations and Notes (Things to Think About)

Term definitions

• Luminous Intensity (candlepower): how bright the light source seems
• Luminous flux (Lumen): measure of light flux irrespective of direction (amount of light through a predefined area)
• Illumination (Footcandle or Lux or Lambert): density of luminous flux on a surface
• Brightness: how much light you get reflected off a surface, the thing that we are really interested in. It's related to Illumination but it is also a factor of the reflectivity of the surface.

2.1 Light and Lighting Systems

1. What color is optimal?
   • Some studies suggest that bluish light provides the most contrast in low light conditions due to eye physiology. However, the human eye is most sensitive to the green/yellow color commonly used on newer road signs.
   • People from warm climates prefer cooler colored light (i.e. blue) whereas people from colder climates prefer warmer colored light (i.e. red, orange).
   • People prefer light in wavelengths similar to those emitted by the sun. These wavelengths fall on the black body radiation curve. Wavelengths of light outside of this curve are generally perceived as unnatural and unpleasant.
2. LEDs come in a range of colors most of which cost the same amount to manufacture even though their market price varies based on color.
3. What is the desired Lumen output? More specifically, what is the desired use of the light?
   • LUTW has found the light produced by their 1 W LED to be adequate for several children to read by. Their 1 W LED lamp produces approximately the same amount of light as a kerosene lamp. That is 18 times less light than a 60 W incandescent light bulb.
4. Eye strain is not directly linked to low-light conditions. Eye strain is caused by fatigue of the eye focusing muscles. This is a common side effect of low-lighting conditions because it causes the reading material to be positioned closer to the face.
5. Fluorescent lights emit low amounts of UV radiation. Other lights such as LEDS and incandescent do not. This UV radiation is usually stopped by inexpensive shields found on most commercially available fluorescent light products in the United States.
6. LED systems generate more heat than one would expect. After a short period of operation, an LED can become hot enough to be uncomfortable to touch but not hot enough to ignite common structural materials such as wood (Paolini, 2003).

2.2 Energy Storage Devices

1. General Info
   • The assumed motorcycle batteries are heavy and not easily portable
   • We believe portability to be key so that our light can compete directly with a kerosene lamp.
   • NiMH batteries have a higher energy storage density and are therefore lighter
   • The chosen battery must be specifically programmed for the perceived charging cycle of the light for maximal efficiency. Using batteries in a manner outside of their design specifications, i.e. deep cycling a short cycle battery, significantly decreases their effective life. Motorcycle batteries, for example, are designed to be surface charged and discharged. They are not intended to be deep cycle batteries.
   • If a NiMH or Lead Acid battery is continually charged without any kind of safety device, the battery will die (Humphrey 2003).
   • Consider mechanical energy storage such as the constant force spring battery currently in use by the Freeplay corporation.
   • Standard electricity generation units such as solar cells produce DC current. To get AC current from such a system an inverter is required, increasing the cost and maintenance requirements.
2. Considerations
   • Lead Acid batteries are much cheaper but have a much shorter life than NiMH batteries
   • A design capable of powering other electrical devices will significantly increase demand for make the system more valuable to the user.

2.3 Charging Devices

1. Photovoltaics aka Solar
   • Although commonly perceived as fragile, recent advances have made them much more rugged and efficient.
   • Two of our three target countries, India and China already manufacture Photovoltaics.
   • They are solid state electronics, similar to LEDs. Without moving parts they are less prone to mechanical failure lasting up to 20 years. However, if they are poorly maintained, they rapidly loose their efficiency
   • Most of the target reasons are in very sunny locals
   • Photovoltaics are easily scalable to meet the needs of the user.
2. LUTW Pedal Generator
   • This generator currently in use by LUTW utilizes human power through a mechanical capture device similar to a tricycle front wheel to drive a flywheel that subsequently drives a generator.
   • It is efficient, reliable and durable.
3. On Grid
   • Users with intermittent electrical access could charge their units using their home outlets. The electricity they stored there could later drawn from their batteries on demand.

3. Bibliography

"Energy Strategies for Rural India: Evidence from Six States." Joint UNDP/ World Bank Energy Sector Management Assistance Programme. Aug. 2002 (http://www.worldbank.org/html/fpd/esmap/pdfs/258-02_intro.pdf).

Lumileds' Website

Interview with Steve Paolini, Director of Business Development, Lumileds, 2003.

Interview with John Humprey, Palo Alto Hardware, 2003.