The intensity should be greater than or equal to:

• A. 100 lx (imperial) or 100 fc (metric)
• B. 50 lx
• C. 500 lx
• D. 10 fc

Answer: (A)

Clear visibility is essential in liquid penetrant inspection so you can detect surface indications after developing. The standard minimum illumination for this visual inspection is about 100 foot-candles, which is roughly 1000 lux. This level ensures small flaws aren’t hidden by shadows or poor lighting.

Why this option fits: it states a minimum around 100 fc (and about 1000 lux in metric terms), matching the required threshold. The other choices represent lighting levels well below that standard (50 lx is far dimmer, 10 fc is only about 100 lux, and 500 lx is roughly 46 fc), so they wouldn’t reliably reveal indications. In practice, aim for about 100 fc or 1000 lux to meet the requirement.