An ND .03 Gel reduces light by what percentage?

• A. 50%
• B. 25%
• C. 75%
• D. 0%

Answer: (A)

Light reduction with an ND gel is governed by its optical density. The amount of light that gets through is the transmission, which is about 10^(-OD). For an ND value of 0.3, the transmission is roughly 0.5, so about half the light passes and half is blocked. That’s a 50% reduction. If you ever see a label like .03, that’s likely a misprint; the standard value that yields a 50% reduction is 0.3. For context, higher densities block more light (0.6 would pass about 25% of the light, a 75% reduction), while zero density blocks nothing (0% reduction).