In the emergency warning world, there is a lot of confusion about SAE and other lighting standards. Let’s dive right in and attempt to shed some light on the subject (sorry…couldn’t resist)…
WHat is SAE?
SAE stands for Society of Automotive Engineers. SAE is comprised of a number of working groups of automotive and lighting engineers that work with industry studies and other experts to set standards.
SAE sets the standards for pretty much everything on a vehicle, from how bright or dim a brake light can be, to lens coatings (in some cases) to thermal performance, to colour specification (is that red brake light really red, or more pink-ish?).
While SAE is not law in most areas, it is a best-practices standard that the entire automotive world pays attention to. Comparing SAE numbers usually gives a good level-playing-field comparison between lights.
SAE publishes thousands of standards, each one numbered. Within each standard, there are usually “Classes” that specify performance. When a vendor says “SAE Compliant” on their website or literature, they should also specify the Standard number and the Class. Without it the term “SAE compliant” is meaningless.
SAE J845 – “Minimum standards for omnidirectional emergency warning lights”
For the sake of this article, I’ll focus on amber beacons (rooftop lights) like the picture here. This is what’s known as an omnidirectional beacon, meaning they shine light in a 360 degree pattern.
The standard for light intensity for this beacon is SAE J845. Within J845, there are three classes:
- Class 1 (brightest)
- Class 2
- Class 3 (dimmest)
Here’s the breakdown of how the compare to one another. Light intensity is measured in Candela-Seconds/Minute (cd-s/m)…
- Class 1 “Clearing Traffic” = 18,000 cd-s/m
- Class 2 “Blocking Traffic” = 4,500 cd-s/m (25% of Class 1)
- Class 3 “Identification only” = 1,800 cd-s/m (10% of Class 1)
As you can see, there is a very dramatic difference between Class 1 and 2. While SAE labels Class 2 as the standard for blocking traffic (your vehicle is stopped and blocking a lane), keep in mind that SAE is a minimum standard.
We always recommend Class 1 unless special circumstances exist such as the vehicle is in a warehouse or a dark mine, etc. and Class 1 might be too obnoxious.
For roadway applications, though, Class 1 is the class to go with if you want the brightest light.
SAE colour chart showing colour ranges for blue (left), white (center), red (far lower right), and amber (right side).
SAE J845 also controls the colour. You may have noticed that some amber (yellow-ish) lights are more of a pale yellow, and some are a richer yellow colour. The pale yellow ones will likely still meet the J845 specification for colour, but just barely.
There are some beacons who use a lighter shade of yellow to get more intensity out of the light (it’s easier to make the light bright if you shine through a pale yellow lens rather than a deep yellow lens).
They run just barely inside the SAE specification. Others, like the Federal Signal lights, tend to have a richer yellow/amber colour that is in the middle of the SAE specification.
You may also see reference to J845 for “directional” lights. This doesn’t mean lights for traffic flow control (sometimes called a Traffic Advisor or Signalmaster) but rather a light that puts out light in a specific direction as opposed to an omni-directional (360 degree) light like a beacon.
While originally designed as an omni-directional standard, J845 has been adopted to a standard that covers a directional light as well. The light must meet certain intensity specifications out to +/- 40 degrees off-axis, and +/- 5 degrees vertically. Note that the peak intensity requirement for J845 directional is lower than J595…
SAE J595 was originally the ‘directional light’ standard and is still used as that. It’s a bit different from J845 in that J595 requires a higher intensity than 845, but only to +/- 20 degrees wide but requires +/- 10 degrees up and down.
This is why you will sometimes see a surface-mounted directional light meet J845 but not meet J595. In that case, it tells you that the light has good off-axis but isn’t necessarily super bright.
If it meets both standards, then it is bright and has good off-axis as well as good up-down light. Ideally your lights should meet Class 1 for both standards.
Also, check the colour for each compliance claim. Often a light will meet Class 1 in red and amber, but not in blue (blue LEDs emit about half the light energy of red so it’s tougher to make blue compliant to a standard that requires high intensity).
California Title XIII
Alongside SAE statements, you may have seen reference to California Title XIII. Title XIII is pretty much the toughest spec for light intensity.
The important thing to note when manufacturers say they are Title XIII compliant is that, like SAE, there are different classes. Title XIII calls them “Tables”.
For omnidirectional beacons, the proper table is Table 2. Some manufacturers will claim that their LED beacon meets Table 4, but that table is for strobe (gas discharge) lights, not LED, and table 4 is a much, MUCH easier table to meet.
Table 2 requires a 12,500 candela intensity and table 4 requires only 125 candela (find out about the difference between lux, lumen and candela). Yes, a 100x difference!
Like SAE, most claims to Title XIII compliance don’t specify the Table number, which as you can see can make a huge difference. If they don’t tell you which table, ask them for details. Our SLR LED Rotator beacon meets California Title XIII Table 2.
Another specification you should pay attention to is CISPR25. CISPR25 is a specification for Radio Frequency Interference (RFI).
While RFI used to be a huge problem with strobe beacons (actual strobe tubes, not LED), it is less of a problem with LEDs but is still prevalent. Like SAE, CISPR25 has standards within it.
Class 1 is the most permissive (allows the most RFI) and Class 5 is the toughest class and is basically zero RFI. RCMP in Canada has the toughest specification in North America for RFI for their emergency lights and they specify Class 3 or better (4 or 5).
Class 1 is very easy to meet, Class 2 is better, and Class 3 is tougher. We recommend you look for RFI specifications of Class 3, Class 4, or Class 5.
Note that some vendors don’t even test for RFI, but it can cause interference with 2-way radios and other electronics. Since beacon lights are generally mounted on the vehicle roof, near the radio antennas, RFI specifications are important.
I hope this helps clear up SAE for you. In summary, the best performance will come from an SAE J845 Class 1 for light intensity, and CISPR25 Class 3 for RFI. If you have any questions, please contact us and we’ll be happy to provide more information.