The National Electrical Manufacturers Association (NEMA) adopted this standard for outdoor area lights back in the 1960's, before conserving energy was a big concern. There are still millions of these fixtures in use in the United States.

Today, several manufacturers, including Hubbell Lighting, Inc., provide full cut-off, clip-on shields to replace the refractor originally used with this fixture. The shield reflects wasted up-light back to the ground for a better quality light.

Here are graphic representations of the light distribution of the NEMA head fixture, with and without the shield.

A number of shields are available for retrofitting existing light fixtures. To find a shield for a particular light, contact the manufacturer. Here is The World's Greatest Lighting Manufacturer List.