The case of the luminous light

By KC Boxbottom in Inspection on November 12, 2014

The phone rang and Janet told me she could not see.

"Can't see?" I asked. "You don't mean you went blind, do you?"

"No, I mean that our vision system stopped being reliable."

"OK, let me get over there and I'll see if I can help you out."

Shortly after, I was in the plant and Janet was showing me her vision inspection system. It was looking for the date code on a carton and seemed to be working properly. As I watched, though, it would sometimes reject cartons with good codes. Worse, it would sometimes accept cartons with bad codes.

It had been working well up to a few days before. So I asked the magic question:

"Janet, what changed? If it was working well before and not now, something changed."

Janet couldn't think of anything obvious so we asked the experts. You know, the people running the line. They told us some fluorescent lamps had been replaced just before the problems began.

"Fiddlesticks on unseeing vision!" I exclaimed. "I'll bet they changed the type of tube."

Checking further won me the bet. The tubes had been cool white, the new ones were daylight. This subtle change in ambient lighting had discombobulated the system camera.

That was not the real mistake. The real mistake happened earlier when the decision was made to rely on ambient lighting.

Sometimes you can get away with it. For bulletproof inspection, a dedicated lighting system is a must.


KC Boxbottom, packaging detective, is on the case to solve tough packaging puzzles. He is the alter-ego of John Henry, CPP. Known as the Changeover Wizard, Henry is the owner of, a consulting firm that helps companies find and fix the causes of inefficiencies in their packaging operations. He produces a free monthly newsletter called Lean Changeover, which contains articles and tips on changeover and related issues. Reach him at [email protected].

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