Ambulance warning light zones explained: NFPA 1900, KKK-A-1822F and CAAS GVS
Written by Shmaya Krinsky, K&K Emergency Systems, Opa-locka, Florida. We build and upfit ambulances, fire apparatus and police vehicles, and we sell the parts we install. Updated October 2026.
Ambulance specifications ask for a warning system with measured optical power in defined zones, at two levels, in two modes. Here is how that works, what the main documents say, and what a purchaser should write into a spec.
The short version
- The vehicle is divided into four zones, A to D, clockwise from the front, at an upper level and a lower level. That is eight measured zones.
- The system has at least two modes: calling for right-of-way (responding) and blocking right-of-way (stopped at a scene).
- Compliance is demonstrated for the installed configuration, by zone and level. A Class 1 rating on one lighthead does not by itself make a vehicle compliant.
- NFPA 1917 (ambulances) was consolidated into NFPA 1900 in the 2024 edition. Which edition governs your build depends on your contract.
- The other common specifications are the federal KKK-A-1822F and the CAAS Ground Vehicle Standard (GVS) V4.0, effective July 1, 2025.
Zones and levels
CAAS GVS V4.0 section C.9.2.1 divides the upper and lower warning levels into four zones designated A, B, C and D clockwise, with zone A at the front, and states that the optical system is divided into eight zones, four upper and four lower. Optical power for each level must be met by the devices in that level, without counting the other level (C.9.2). The same V4.0 text sets the optical center of upper-level devices at 102 in. or less, and lower-level devices between 18 in. and 48 in. above level ground. Federal Signal's NFPA 1900 ambulance configurator describes the same upper-and-lower, eight-zone structure.
Calling and blocking modes
GVS V4.0 C.9.2.8 requires a master switch that energizes all optical warning devices and at least two signaling modes: one signaling that the ambulance is responding and calling for right-of-way, and one signaling that it is stopped and blocking it. Any change within a mode must still meet the minimum requirements. The table shows the zone color permissions from V4.0 Table 2, "within the constraints imposed by applicable laws and regulations":
| Color | Calling for right-of-way | Blocking right-of-way |
|---|---|---|
| Red | Any zone | Any zone |
| Blue | Any zone | Any zone |
| Yellow | Any zone except A | Any zone |
| White | Any zone except C | Not permitted |
| Green | Any zone | Any zone |
V4.0 also says green optical energy does not count toward a zone's total optical power. The optical power minimums are in V4.0 Table 1, in candela-seconds per minute. The horizontal-total column, from the published PDF:
| Zone | Level | Calling, H total | Blocking, H total |
|---|---|---|---|
| A | Upper | 1,000,000 | 400,000 |
| B | Upper | 200,000 | 200,000 |
| C | Upper | 400,000 | 800,000 |
| D | Upper | 200,000 | 200,000 |
| A | Lower | 150,000 | 150,000 |
| B | Lower | 75,000 | 75,000 |
| C | Lower | 0 | 0 |
| D | Lower | 75,000 | 75,000 |
Table 1 also has per-point minimums. Do not copy these figures into a purchase specification from this page; take them from your own copy of the standard. These are CAAS values, not NFPA values.
Compliance is for the installed system
V4.0 C.9.2.7 lets the final-stage manufacturer demonstrate compliance in one of two ways: certification that devices were installed within the manufacturer's geometric parameters, referencing the device maker's certification that the system meets the zone and level minimums, or a certified calculation from the photometric test reports of individual optical sources showing the combination as installed meets them. C.9.2.5 says testing is done by, or on behalf of, the device manufacturer to SAE J845, and that photometric data must be available on request. V4.0 C.9.2.2 requires 60 to 240 flashes per minute for each optical source. V4.0 also caps the maximum continuous electrical load of the optical warning system at 540 watts, which is a CAAS limit and not a wire, fuse or total vehicle electrical design, and requires enough sources per level and zone that one failed source does not leave a measurement point without a visible signal at 100 ft.
That is why the zone layout and the lightheads should be specified as a set. A lighthead's SAE class does not establish ambulance compliance; the final-stage manufacturer must demonstrate that the installed system meets the applicable specification. See our SAE class post.
The documents
NFPA 1900, 2024 edition. NFPA 1900's 2024 edition consolidates NFPA 1901, 1906, 414 and 1917; its ambulance application provisions use a January 1, 2024 contract-date threshold, subject to the applicable authority, contract and requirements for new or remounted vehicles. NFPA 1917's ambulance content now sits within it. For an NFPA-specified build, obtain the issued 2024 standard and confirm the applicable ambulance warning-light provisions and tables with the final-stage manufacturer. This page does not give NFPA table values.
KKK-A-1822F. The federal Star-of-Life specification is dated August 1, 2007 and amended by GSA change notices. GSA Change Notice 14, dated July 15, 2021, replaced section 3.8.2 and its subsections, including SAE J845 test procedures. This article does not establish which change notice is current. Confirm the current revision with GSA, and obtain the complete applicable GSA change-notice set for the contract.
CAAS GVS V4.0. Effective July 1, 2025. Lighting is in section C.9.2, as described above. GVS V4.0 also cites SAE J578 for the colors, and FMVSS 108 for the basic exterior lighting.
What a purchaser should put in a spec
- The document and edition: for example NFPA 1900-2024, KKK-A-1822F with the change notice you mean, or CAAS GVS V4.0.
- The required compliance evidence: a zone-by-zone layout and the manufacturer's certification or photometric calculation for the installed configuration.
- The modes you need and who approves flash patterns.
- The color permissions your state allows.
- The electrical load limit and the charging and battery capacity to support it.
Frequently asked questions
Is a Class 1 lighthead enough to meet NFPA 1900? No. Compliance is for the zone and level of the whole installed system.
Does the 2024 NFPA 1900 apply to my existing ambulance? Not automatically. The edition adopted by your authority or written in your contract governs.
Do I need lower-level lights in every zone? Under GVS V4.0 Table 1, lower zone C is listed at zero. That applies to the optical-power table only; it is not an exemption from required stop, tail, turn or other exterior lights. Confirm in your own copy of the standard.
Can I use white lights in blocking mode? GVS V4.0 Table 2 says white is not permitted in blocking mode. Local law may restrict colors further.
Who tests the lights? The device manufacturer, or a lab on its behalf, per GVS V4.0 C.9.2.5.
Browse emergency lighting, light bars, perimeter lighting and scene and compartment lighting, or call (305) 317-2619 with your specification and we will help build a zone layout to it.
About this article: it was drafted with AI assistance and fact-checked against the standards bodies and manufacturer publications cited in the text. AI-written content can contain errors and standards change, so facts here may be wrong. Where we describe our own practice, it is our practice, not a requirement of any standard. Confirm any requirement with the standard, the manufacturer, or with us before you buy or install.