What are the permitted light pulse durations?

• A. 10-50 milliseconds
• B. 20-100 milliseconds
• C. 50-150 milliseconds
• D. 100-200 milliseconds

Answer: (B)

Understanding how long a visual alarm pulse lasts helps ensure the light is clearly noticed without being uncomfortable. The permitted pulse duration needs to be short enough to register as a quick flash, yet long enough for people to perceive it reliably. A range of 20 to 100 milliseconds hits that balance: pulses shorter than 20 ms can be missed, especially in busy environments, while pulses longer than 100 ms can read as a continuous light and cause glare or discomfort. This aligns with common NFPA 72 requirements for visible notification appliances, which call for brief, perceivable flashes that still feel distinct from a steady light. So, the 20–100 ms window is the correct standard for permitted light pulse durations.