I didn’t trust incident meters at all. They only told me how much light was falling on an object but didn’t tell me anything about how bright the object itself was. I felt like I was working in the dark with an incident meter, and I held others in disdain when I saw others using incident meters to average exposures across multiple light sources. In my head I thought, “You’re averaging light sources! How can you possible know what’s going on with any single light?"

Read the full article:The Rough Guide to Calibrating a Light Meter in the Field at DV Info Net (http://www.dvinfo.net/article/optical-science/the-rough-guide-to-calibrating-a-light-meter-in-the-field.html)