What is the difference between SAE Class 1, SAE Class 2 and SAE Class 3 Warning Lights?

Understanding SAE Class for Vehicle Safety Warning Lights 

This article explains in basic terms how SAE class is determined, when it is used, and the difference between the three SAE classifications for warning lights. Click on these links for our SAE rated lights: Class 1, Class 2 and Class 3.

The Society for Automotive Engineers (SAE) has established a standardized classification system for vehicle warning lights. This system is called SAE Class and there are three levels: Class 1, Class 2, and Class 3. Before we explain the differences between the three classes, let’s begin by understanding how SAE Class is determined.

SAE Class is determined using the SI unit of measurement, Candela. Candela (cd) is a quantifiable measurement of brightness and refers to the intensity of a single beam of light in a particular direction. The SAE relies on candela to create its class rankings because automotive warning lights typically use concentrated beams of light to alert oncoming traffic of potential danger or hazard. Using another unit of measurement, like lumens for incandescent bulbs, would be ineffective since lumens represents the total area illuminated by a light, rather than the distance from which the light can be seen. Imagine a standard incandescent light bulb with a high lumen value placed on top of an ambulance. Though it would successfully light up the area around the ambulance, it would likely do very little to alert distant vehicles of an emergency. However, when an ambulance uses a focused beam of light with a low lumen value but high candela value, the light can be seen from miles away. Simply put, the larger the candela value, the greater the intensity and visibility of a light over extended distances. 

What is the difference between SAE J595 and SAE J845?

When choosing the best light for your application, you may come across the identifiers SAE J595 and SAE J845 followed by Class 1, Class 2 or Class 3. It is important to note that these titles refer to the functionality of light and that the SAE Class ratings are equivalent in both instances. SAE J595 refers to directional flashing optical warning lights (think flashlight pointed in a single direction). SAE J845 refers to omnidirectional or 360 degree optical warning lights (think lighthouse or emergency vehicles). The distinction between these two categories lies in the direction of the light--directional, which is only visible from a particular direction or omnidirectional, which is visible from all directions. While these categories are distinct, the light intensity is measured the same. Therefore, a SAE J845 Class 1 warning light and a SAE J595 Class 1 warning light can be equal in candela output (intensity); the only difference is that the SAE J595 Class 1 warning light can be seen only from a singular direction while the SAE J845 Class 1 light can be seen from all directions (360 degrees).

What is the difference between SAE Class 1, SAE Class 2 and SAE Class 3 Warning Lights?

SAE Class 1 Warning Lights
SAE Class 1 Warning Lights are most often used for emergency response vehicles such as police, fire and ambulance. Lights in this class have a candela value greater than 8100, with some reaching close to 18,000 cd-s/m when used to clear traffic in emergencies. SAE Class 1 lights are 4 times more intense than SAE Class 2 lights and 10 times more intense than SAE Class 3 lights. 

SAE Class 2 Warning Lights
SAE Class 2 Warning Lights are commonly used on utility and service vehicles moving at or below the speed of traffic. Candela values in this class range from 1981 cd to 8099 cd-s/m. Vehicles that are slow-moving or blocking traffic typically have warning lights with a candela value close to 4,500. SAE Class 2 lights are approximately 2.5 times as bright as SAE Class 3 lights.

SAE Class 3 Warning Lights
Because SAE Class 3 Warning Lights have the lowest light intensity of the three SAE classes, they are typically used inside of buildings where there is little or no ambient sunlight. Class 3 warning lamps may be used on forklifts, specialized machinery, or for an attention-grabbing effect at trade shows and indoor events. 

The requirements for warning light classification requirements vary based upon the jurisdiction and application. We recommend that you consult with your local jurisdiction to determine which classification of lights is appropriate for your application.