| Continued from above... flame with reflectors behind it still lost 83% of its light, the Fresnel lens was able to capture all but 17% of its light. Because of its amazing efficiency, a Fresnel lens could easily throw its light 20 or more miles to the horizon. |
Seven types, called "orders," of the lens were developed. The first three largest orders were for seacoast lights, while orders four through six were smaller, for harbor or bay lights. There was also a 3.5 order lens which was used mostly in the Great Lakes.
Source: The Fresnel Lens, http://lighthousegetaway.com/lights/fresnel.html