Fruit sorters need more light

Agricultural Research, June, 1995 by Ben Hardin

Packinghouse managers concerned about cherries erroneously graded as Extra Fancy came to ARS and Michigan State University scientists at East Lansing with their problem.

As the sorters discarded defective cherries from among hundreds passing by each minute, cool white fluorescent bulbs emitted low-intensity light that also reflected from white uniforms, a white conveyor belt, and stainless steel tables. Eyestrain tired the workers physically and mentally.

Since the produce industry lacked information on ideal lighting, ARS agricultural engineer Galen K. Brown and his colleagues conducted studies and published guidelines in 1994.

They recommend less highly reflective colors in the cherry sorters' clothing and surroundings, different low-cost fluorescent lamps above workstations to provide light with higher intensity, and a broader range of wavelengths and dark conveyor belts or rollers.

When packing lines were remodeled, experienced cherry sorters performed their jobs with greater accuracy and were much less tired at the end of the day. Results have been similar for apples, blueberries, cucumbers, onions, and other produce.

"In our studies, we identified light sources that accentuated rather than masked the eyes' perception of color differences between defects and sound tissue," said Brown.

On most fruits and vegetables, 3,000 [degrees] K (Kelvin) fluorescent light that accents brown colors will best reveal defects caused by insects, rots, diseases, and mechanical and natural injuries. But on potatoes, a green-skin defect can be seen most easily in a 6,500 [degrees] K fluorescent light that contrasts green against the tubers' normal skin color. Dark-colored produce will require twice the light intensity as light-colored produce.

Eye sensitivity to light is known to decrease with workers' age. So sorters about 50 years old and older should work under about twice the intensity of light needed by sorters in their twenties.

Just as the researchers were finding that cool white fluorescent lamps had long hampered produce sorters' proficiency and comfort level, U.S. federal energy standards coincidentally banned their manufacture. Neither 8-foot nor 4-foot cool white tubes will be made after October 1995. This prohibition will soon make more likely the selection of light that provides both better sorting and energy efficiency.

Galen K. Brown is in the USDA-ARS Fruit and Vegetable Harvesting Research Unit, Michigan State University, East Lansing, MI 48824; phone (517)-353-5185, fax (517) 353-8982.