Rods are positioned away from the central axis of the retina, which means that in very low light you have to look slightly to the side of something in order to see it.

Current ways of measuring how much light is present, for setting standards in offices and schools, for example, only relate to cones.

This means that in low light levels, where both rods and cones are operating, measurements of how much light is present are inaccurate. This is reflected in the practical and inexpensive nature of current more primitive light meters.

Now researchers from the Lighting Research Center at Renssalaer Polytechnic Institute (RPI) in Troy, NY, have developed a new light meter that accurately characterizes this shift from rod to cone vision -- and that is cheaper and less bulky than the very expensive and sensitive instruments that are only practical for use in a laboratory.

Published today in the UK Institute of Physics journal Measurement Science and Technology, this new retinal flux density meter will provide an affordable tool for measuring light at all levels and might ultimately lead to new standards to improve both energy efficiency and safety at night.

"Conventional light measurements are accurate when light levels are suitable for activities like reading and threading needles, but are not good in low light conditions when both rods and cones in the eye are detecting light," said Dr. Van Derlofske, Head of Transportation Lighting at RPI's Lighting Research Center. "For example, we use our peripheral vision, or rods and cones, in a dark alley to detect someone moving towards us from an oblique angle," he said.

The new light meter has an extra filter that can not only calculate the amount of light the eye's cones would see, but also the amount of light that the rods would see. The device even approximates the optical properties of the eye, including shielding from the nose and brow and the optics of the cornea and lens.

"Although the prototype device is not yet available commercially, we estimate it would cost just half the price of the existing lab-based technology, and be much more accurate than the smaller portable devices currently on the market," said Dr. Van Derlofske.

The Institute of Physics is a leading international professional body and learned society with over 36,000 members, which promotes the advancement and dissemination of a knowledge of and education in the science of physics, pure and applied. It has a world-wide membership.

The Institute is a member of the UK's Science Council and a nominated body of the Engineering Council. The Institute works in collaboration with national physical societies and plays an important role in transnational societies such as the European Physical Society, and represents British and Irish physicists in international organizations.

In Great Britain and Ireland, the Institute is active in providing support for physicists in all professions and careers, encouraging physics research and its applications, providing support for physics in schools, colleges and universities, influencing government and informing public debate.


[Contact: Dr. John Van Derlosfske, Alice Bows]

02-May-2002