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Figure 1. Los Angeles, 1908

Figure 1.1 Los Angeles, 1908

Light pollution or sky glow is caused by light aimed directly up into the sky and by light reflected off the ground or objects. Sky glow prevents the general public and astronomers from seeing the stars.

Floodlights, wall packs and other un-shielded luminaires are the major contributors to sky glow. Overlighting, even with shielded luminaires, reflects unnecessary light back into the atmosphere and adds to the sky glow. This often occurs at outdoor areas such as motor pools and sports fields.

To minimize light pollution, use fully shielded luminaires or IESNA full cut-off type for area and roadway lighting as illustrated in Figure 3.

Unshielded and non-cutoff luminaires lead to light pollution.

Figure 2. Unshielded and non-cutoff luminaires lead to light pollution.

The use of full cutoff luminaires may reduce uniformity and therefore require greater pole heights or spacing. Cutoff, semi-cutoff, and non-cutoff luminaires may also be used at low mounting heights if the lumen output of the lamp is limited to 4200 lumens.

These applications, such as pedestrian and entry lighting, typically require greater vertical illuminance for facial identity.

Figure 2. Los Angeles, 1976 (right)

Figure 1.2 Los Angeles, 1976

Provide uniform low glare lighting and do not overlight exterior areas. Also, control lighting with time clocks, photocells, and motion sensors such that lighting is only energized when needed.


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Thin Film Solar

Thin Film Solar

While silicon is the industry common semiconductor in many electric units, which includes the photovoltaic cells that pv panels use to transform sunshine into power, it is not really the most efficient material on the market.

For instance, the semiconductor gallium arsenide and associated ingredient semiconductors give nearly double the performance as silicon in solar devices, but they are rarely used in utility-scale applications because of their excessive manufacturing cost. University of Illinois. ( teachers J. Rogers and X. Li explored lower-cost methods to produce thin films of gallium arsenide that also made possible usefulness in the types of products they might be integrated into.

If you can minimize significantly the cost of gallium arsenide and some other compound semiconductors, then you might expand their range of applications.

Usually, gallium arsenide is placed in a single thin layer on a small wafer. Either the ideal device is created right on the wafer, or the semiconductor-coated wafer is cut up into chips of the desired size. The Illinois group made the decision to put in several levels of the material on a simple wafer, producing a layered, “pancake” stack of gallium arsenide thin films.

If you grow ten layers in 1 growth, you simply have to fill the wafer one time. If you do this in ten growths, loading and unloading with temp ramp-up and ramp-down take a lot of time. If you consider exactly what is needed for each growth – the machine, the preparation, the time, the workers – the overhead saving this solution gives is a important expense reduction.

Following the researchers independently peel off the levels and transfer them. To accomplish this, the stacks alternate layers of aluminum arsenide with the gallium arsenide. Bathing the stacks in a solution of acid and an oxidizing agent dissolves the layers of aluminum arsenide, freeing the individual small sheets of gallium arsenide.

A soft stamp-like system picks up the levels, one at a time from the top down, for shift to another substrate – glass, plastic-type or silicon, depending on the application. After that the wafer can be used again for another growth.

By performing this it’s possible to create a lot more material much more rapidly and much more price efficiently. This process could produce bulk quantities of material, as opposed to simply the thin single-layer manner in which it is usually grown.

Small Sheets Of Gallium arsenide

Small Sheets Of Gallium arsenide

Freeing the material from the wafer additionally opens the chance of flexible, thin-film electronics made with gallium arsenide or some other high-speed semiconductors. To make products that could conform but still keep higher efficiency, that is significant.

In a paper written and published on-line May 20 in the publication Nature (, the team details its methods and shows three types of products using gallium arsenide chips manufactured in multilayer stacks: light products, high-speed transistors and solar cells. The authors also provide a comprehensive cost comparison.

Another benefit of the multilayer method is the release from area constraints, particularly important for photo voltaic cells. As the levels are eliminated from the stack, they may be laid out side-by-side on one more substrate to generate a significantly bigger surface area, whereas the typical single-layer procedure limits area to the size of the wafer.

For photovoltaics, you want big area coverage to get as much sunshine as achievable. In an extreme case we could develop adequate layers to have 10 times the area of the traditional.

After that, the group programs to explore more potential product applications and additional semiconductor materials which could adapt to multilayer growth.

SOURCE: University of Illinois Researchers Demonstrate Us Little Known Methods to Produce More Efficient Solar panels

AUTHOR: Shannon Combs |

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