Question
One of our shippers is putting in new lighting over grade tables and is asking for some direction on specific lighting to facilitate grading of oranges. I understand you have done some pretty extensive studies in this area. Anything you may have on both in reference to energy efficiency and to effective grading of produce would be of value. (R.E.)
Answer
There are some fairly straight forward concepts to keep in mind when designing a lighting system:
1) Light levels at the belt should be 50 to 100 foot-candles (500 to 1000 lux)
2) Cool white fluorescent lamps provide good color rendition for sorting and are energy efficient. Lamps with a high color rendering index (CRI) are best. CRI numbers range from 0 to 100. In some cases special light sources can be selected to bring out difficult-to-see defects. This would need to be done in a lighting laboratory where the fruit could be evaluated under a range of light sources. Southern California Edison has a facility like this.
3) Sorters should not have surfaces in their field of view that vary in luminance (level of reflected light) by more than 3 to 1. For most fruit, conveyors should be a medium gray color and sorters should not wear white aprons.
4) Lights should be installed so that the sorters cannot easily see the lamps.
5) Food safety requirements dictate that the lamps be covered to prevent broken glass from contaminating the product.
--Jim Thompson