You've accurately observed the shift in NFPA 72 toward UL 1638 for visual signaling device requirements. Let's break down your understanding and the implications for your 15/75 cd horn/strobe: UL 1971 vs. UL 1638

You're correct. NFPA 72 has increasingly favored UL 1638 for visual notification appliances. UL 1971 primarily covers notification appliances for the hearing impaired, focusing on temporal patterns and tactile notification. UL 1638 focuses on visual appliances.

Your 15/75 cd Horn/Strobe

This is where it gets nuanced. The device is listed for 75 cd under UL 1638. However, the key consideration is what type of application you're using the notification appliance in. UL 1971 (Private Mode Emergency Signaling) requires the notification appliance to be installed with a certain light distribution pattern and the coverage requirements are much more stringent than UL 1638. UL 1638 (General Visibility) focuses on the general visibility for general signaling applications such as mass notification systems or wide-area alerting.

Meeting the 60 cd Requirement

If your application falls under a general signaling environment, then

yes, a 75 cd UL 1638-listed strobe likely meets the requirement. However, If you are looking for Emergency Signaling for the hearing impaired and your application requires UL 1971 notification appliances, a device listing for 15cd might require many more notification appliances and/or be rejected by the AHJ.

Recommendation


Consult the AHJ

This is the most important step. Explain the situation to your local Authority Having Jurisdiction (AHJ) – the fire marshal, building inspector, or whoever enforces NFPA 72 in your area. Present them with the device's listing information and your intended application. Ask specifically if a UL 1638-listed device is acceptable in your scenario.2.

Document Everything

Keep a record of your conversation with the AHJ, including the date, the AHJ's name, and their response. This documentation will be vital if questions arise later.3.

Check NFPA 72 (2025)

Carefully review the sections of NFPA 72 (2025) that pertain to visual notification appliances, specifically Chapter 18. Understand the requirements for spacing, placement, and coverage based on the application type. Also, familiarize yourself with any amendments or local ordinances that may apply in your jurisdiction.
4.

Consider the Application

Again, what is the purpose of the horn/strobe? Emergency Fire Evacuation for building occupants? General Signaling for a mass notification system? The application dictates the relevant standard (UL 1971 vs. UL 1638).5.

If in Doubt, Err on the Side of Caution

If the AHJ is unsure or if you're still uncertain after reviewing the code, it's safer to use a strobe specifically listed for 60 cd under UL 1971, if your goal is compliance for emergency evacuation.6.

Consider other solutions. In many installations, the use of addressable notification appliances can change coverage requirements for the space.

In Summary:

While the trend is toward UL 1638, the applicability of your 75 cd strobe depends on the specific application and the interpretation of the AHJ. Don't assume it's automatically acceptable. Consulting with the AHJ is crucial. Flag for review