Are home security alarms necessary in apartment buildings. We own our condo and were considering installing a home security alarm. What do home security alarms do, what are they capable of ? Is it worth paying $ 30 a month for an alarm ? Is Brinks a good name in the alarm industry. Thanks in advance for any suggestions or ideas.
Most auto supply, welding supply, or tool stores carry a variety of full face shields.
Sorry, but I'm not quite sure what your question is. Thus to me it appears to touch on several different optical principles. For the application you cite where the light has to be transmitted through the material, as in car headlights, the design concern is beam shaping which is controlled in part by the lens in front. The optical principles used there are both Fresnel and prism optics. Since you ruled out the prism aspect, the term you may be looking for is 'Fresnel'. For systems that depend only on reflected light such as bicycle reflectors and reflective clothing patches, the term you may be looking for is 'retro-reflector' or 'total internal reflection'. These are systems that rely upon geometry such as corner cube reflectors or glass-beads with total internal reflection to bounce the light back 180 degrees. Hope this is of some assistance. Gregg
Well into the 18th century, astronomers mainly used long refracting telescopes, designed around a meticulously shaped glass lens. However, other telescope designs offered a way to avoid some of the defects that could not be avoided in refractor lenses. In 1668, Isaac Newton devised a reflecting telescope. Instead of a lens, it used a single curved main mirror, together with a smaller flat mirror. In the next century, huge instruments descended from Newton's design turned out to be especially useful for studying very faint objects, such as the dim patches of light known as nebulae. The studies that the new and bigger tools made possible led to fundamental changes in our understanding of the universe.
