Thank you for providing these instructions and Excel Worksheet Ralph.

page 3/8 of the pdf says "Film has a different sensitivity to different wavelengths of light. Therefore, select a light source with a color temperature representative of your typical subject matter and setup."

How do I measure the colour temperature of my light box upon which I will place the Stouffer step wedge ? Can I do this with a digital camera ? I'd like to ensure it is close to daylight.