It was well understood that with our limited time and finite budget an entirely original concept would be a near impossible task. The group researched other means of power and lighting that are already in place to reach a model that could meet our customer needs the best. Benchmarking was performed throughout the design and concept selection fazes of this project. The individual components of the chosen design can be attributed to other products, but before that, complete LED lighting systems were investigated to gain an understanding on what a new design should aim for. In fact, there are a few organizations with similar goals in mind; for example "light up the world foundation" or "the Lumina Project" which both aim to provide off-grid lighting for developing nations through charitable donations. Both of these organizations have been providing light for impoverished people around the world; however the asking price per unit is astronomical considering the daily income of the target customer. And so, the supply of lighting systems is not based on their demand, but on the willingness of wealthier patrons to contribute. This analysis, along with customer feedback, provided a specification for an affordable lighting system.
Some of the first few concepts that were considered involved a dynamo crank system to utilize physical motion as a power source. There are a number of different camping lights on the market with the same power source. Two of these products were acquired and studied for their light output, ergonomics and component sizes. The main criticism for these types of products was that they produced a short lighting time for a large amount of physical exertion. None of the products that were found had a design that was ergonomically structured for an extended charging time. This reality and the goal for a simplistic design with few moving parts effectively rejected using a crank.
Since a direct power application will not meet our customer needs for a long light output, some form of battery is necessary. Lithium Ion batteries and Super Capacitors were vetoed simply based on their cost. Lead Acid and Nickel Metal Hydride batteries were purchased to compare their capacity and size. It was understood that Lead Acid batteries were considerably larger, and now there is no question. The size and weight of a Lead Acid battery with enough power to meet customer needs would significantly limit the lighting module design to a bulky, heavy device.
Since the light output is highly ranked in customer needs, and because Lumens and Lux are difficult metrics to mentally perceive, a lot of time was spent benchmarking the light distribution subsystem. Using a Lux meter and a meter stick, measurements were taken to compare the light intensity at various distances for multiple lighting methods. The first round of benchmarking tested different light sources (incandescent bulbs, LED's, Kerosene Lamps and candles) at half meter increments. From this, it was concluded that LED's would effectively improve the lighting conditions of the target users. Because LED's are well known for their uneven and narrow lighting, the light diffusion associated with different lenses was also tested. LED's without lenses were tested alongside prismatic, frosted, wide angle and rippled lenses. The results were clear, defining a prismatic lens as the preferred light diffuser.
Graphical Comparisons from Benchmarking
The following plot allows for some perspective as to the lighting levels we are dealing with. In this case the LUX meter was used to compare incandescent, fluorescent, and LED lighting. Under the conditions tested it may be seen that a single LED is roughly equivalent to a 100W incandescent light bulb.
To further add perspective to the proposed lighting solution, this second plot performs a similar comparison but with lighting solutions currently available in developing nations.
The final plot shows the effect of lenses on the lighting abilities and distributions of the LED's. It was from this work that the prismatic lens was determined to be the preferred light diffuser.