How to Pass Lemons (Lighting) Tech

The Easy Way: They Spent Billions of Dollars to Help You Race

So you want to do a 24 Hour Race?  Consider yourself warned: The romance of the 24 hour is way better than the actual experience.  But if you’re committed to doing it, you have to worry about lights.  The Lemons rules (section 3.10.11) cover requirements.

But here’s the secret to passing Lemons Tech when it comes to lighting:

  1. Install the OEM lights on your car
  2. Aim the headlights properly, and verify they both work
  3. Verify that you have a working rear running light and a brake light
  4. Make sure your vehicle numbers are lit/visible so corner workers can see them

That’s it.  OEM lights are actually very good on track!  The large automotive manufacturers spent billions of dollars making them bright enough to see that deer on the side of the road while not blinding other drivers.  And they are reliable enough that you can use them to find your way to the junkyard after many other things on the car have failed.  You should leverage that if you can.

The Best Upgrade: Apex Lights

There is a single upgrade to your OEM lights that are high value, and won’t annoy other drivers: Apex Lights.  Apex lights are explicitly designed to make it easier to see the corners.  They are usually mounted on the outside corners of the car, pointed horizontally at 30-45 degree angle and are meant to illuminate an apex.  Some people mount them to point across the car, and this gives the widest beam.

The best apex lights will have a fog pattern.  A fog pattern is wide and low with a very clear hard horizontal cutoff.  The best ones will also have a very low color temperature 3k or so.  They should look yellow.

Here’s an example of a car with two Ford Ranger lights mounted in buckets with apex lights pointed outwards.  This had great visibility for the drivers in the car, didn’t annoy other drivers on track, and won the 24 hour HPR race in 2022:

Aim Your Lights

The single best thing you can do to have a good on-track experience is to aim your lights ahead of time.  If the driver can’t see they can’t drive confidently.  So make the time to do this!  

Headlights

The goal with this process is to get a 2 inch drop over 25 feet for the top of the car’s low beams.  Here’s how to aim your lights:

  1. Find a level area with a wall.  You will need 25 feet between the car and the wall to measure your lights.  You will also need a measuring tape to get the height of the lights, some blue tape to mark the height on the wall, and some cardboard to cover each light.  And you need headlights with working low beams.  (Remember what we said about OEM lights - they are good!)
  2. Put someone in the car with a half a tank of fuel or more
  3. Measure the distance from the ground to the middle of the lights - this is your baseline height
  4. On the wall 25 feet away, put blue tape on the wall at the height you measured to the center of the lights
  5. Turn on the car’s low beams.  Cover or disconnect one light so you’re only adjusting one light
  6. Good low beam lights should have a hard cutoff of light.  This hard cutoff should be just below the height you measured.  A 2 inch drop over 25 feet makes for a well-aimed beam
  7. Adjust the horizontal so that the center of the beam is straight ahead

That’s it!  Your lights are aimed.  While you will likely be using the high beams on track, you can use the low beams to get them properly set up since they have the hard cutoff.

Apex Lights

If you’ve got apex lights, and you were smart enough to get a fog pattern, set them up to be adjustable if you can.  The best way to adjust these is by doing night testing.  While headlights can be adjusted to be straight ahead, the apex lights are going to be a combination of where the turns are, how fast you’re approaching them, and might be different side to side depending on the track.  So start with something that throws light out to the corners, out to about 25 feet or so while pointing down.  If they are blinding from straight ahead at 30 feet, then they are either really bad lights, or they aren’t pointed out far enough.  Note that the lemons rules require a hard cutoff at 40” - including Apex lights!  So make sure they don’t spill everywhere in front of the car.

Door (and Roof) Numbers

You will need door numbers to drive at night as well.  And a roof number, too.

  • Your door numbers will need to be very easy to read from corner stations.  They will need to be actively lit.
  • Your roof number will need to also be actively lit (as of 2025 25h @ Thunderhill.) Be visible from the start/stop stand.  There’s generally light shining down from the start/stop stand, so reflective tape is acceptable for a roof number.

Possible options for this include:

  1. License Plate Lights: Using an external light like a license plate assembly.  Rockauto sells full assemblies in both non- and LED types. ($15-$40) - These suck, do not use them.
  2. EL Display: You can use something that backlights like an EL display, and then have some vinyl allow the light to only show through the number portion.  There are online places that sell pre-made ones, too.  (These are for Real Racers and therefore probably $$$.)  And another example of building one in a NASA blog ($200-$300 + vinyl/etc.)
  3. LED Display: Described below, you can use an LED backlit display ($45-??? + vinyl/etc)
  4. Reflective Tape: Use only for your roof number, as mentioned above

Do you want to save money?  Here’s one recipe for how to build some backlit door numbers on the cheap, via Jeff Keacher, which is also available in video form: Make a Backlit Racecar Number Board For Less than $40 | *A Brief Tutorial*

1) Get an A3-size LED light board from Amazon. We used the one with the name that started "Light Board A3, 16.6×12.6inchs Light Pad", from the pseudo-brand Lyangx. It's about $20 right now.

2) Take the LED light board apart by gently prying the translucent top off of the opaque bottom (they're held together only by double-sided tape)

3) Desolder the red and black (positive and negative) wires from the LED strip inside the light board case. Solder longer lengths of wire to each of those points on the LED strip and route the wires out of the case through one of the holes vacated by the buttons on the control board that you removed. If you're planning to power it with something like a 12V to USB adapter, you can cut apart the included USB cable and wire in directly with that. Remove the no-longer-needed control board. (This step is necessary because as delivered the light board won't come on when power is applied until its power button is pressed. This step also allows the water resistance to be improved.)

4) Put electronics-safe (non-corrosive) silicone RTV/potting compound around the perimeter of the interior so that you can stick the translucent top back on the opaque bottom. Add a little extra silicone around the wires you soldered on so that water can't get in there. (You might also try two-sided tape, one-sided racer's tape around the outside edge, etc.)

5) Make (or have made) vinyl numbers, reverse-cut so that the vinyl covers everything except the numbers. Stick the vinyl to the board. For added security, use a little 3M Primer 94 to get the vinyl to stick better to the translucent plastic, or cover the whole thing with something like 3M clear film.

6) Power the board using the wires you added in Step 3. Give it 5V. Each board draws about 900 mA (ignore the ridiculous power claim in the Amazon listing). As mentioned earlier, you can use a 12V to USB adapter. An inline fuse wouldn't be a terrible idea.

Done!

Alternative ideas include: use spray paint and templates instead of vinyl; use tinted translucent vinyl; or add a PWM control to allow variable brightness. I'd be curious to hear other ideas!

But I want MORE LIGHT because if I have MORE LIGHT I can WIN

OK so you’re going to ignore all of the above advice and you want to do something that you think will give you more light?  Fine, let’s talk about that.  First of all, the rules state:

Headlights & Driving Lights. On level ground from 25 feet away, forward-facing lights must have a hard cutoff at 40″ or less off the ground. While good-quality, properly aimed OE headlights are generally up to the task, aftermarket driving lights are legal. A small number of high-quality, properly mounted, correctly aimed headlights or driving lights is much more effective than a large number of crappy add-ons. Unfocused LED light bars are almost certain to get you black-flagged.

If you want to add more light, you need to do so in a way that doesn’t offend other drivers and get you black flagged.  If another team comes to the judges and says “hey, this car out here is completely blinding others” it’s likely they will call you in.  And you will be sad.  Don’t be sad.

Here’s advice that you might not have considered - the easiest way to add more light is to add more OEM lights.  Remember that cars from the 80s and 90s had sealed beams, and you can mount those on your car.  The car above is a bent up BMW, and is running lights for a 1987 Ford Ranger mounted in a 5x7 bucket for Kenworth & Peterbuilt trucks.  And because they have a good low beam and high beam setting, you can actually aim them.  If you look at the listing for the lights for the Ford Ranger above you can order from reputable brands (Philips, Wagner) for under $15 and even get “Extra Bright” versions for an extra $4.  You could also go with a four-light setup that was common on 80s GM cars and trucks with 4x6 lights.  For example, here are lights for a 1984 Cavalier.  And you can get a mounting bracket from Dorman for Kenworth T800s.

This Doesn’t Sound Like Enough Light And I Said I Want To WIN With LIGHT

OK fine, don’t follow the advice and use the mass market options that are cheap and reliable.  Here are all the things you should think about if you want to go down the path of doing something else.  This covers:

  • Beam pattern
  • Color temperature
  • Lighting tech
  • Power budget
  • Connectors
  • Mounting
  • Reliability

Beam Pattern

This is the single most important thing to think about when it comes to lighting selection.  And it’s the thing that if you get wrong, will land you in the penalty box.  There are tons of videos on youtube that show different beam patterns (quick overview) but here’s the short version:

Good:

  • SAE Driving (Front-facing lights)
  • Has low & high beams that are selectable, and the low beam has a very hard cutoff so you can aim them
  • SAE Fog (Apex Lights)
  • Hard cutoff often with a yellow color

Mediocre

  • Non-SAE Fog (Apex Lights)
  • Spot Pattern (Apex Lights)
  • Good luck passing the 40” rule with these

Bad:

  • Any flood pattern
  • …which is most LED light bars, LED cluster lights, or (likely) any LED-powered lights under $200
  • Poorly done HID conversions

Really bad:

  • High color temperature lights (which is a lot of cheap LED lights)
  • Almost any offroad LED light bar.  Just stop using them.  They won’t pass tech anyway.

Color Temperature

Huh?  What’s that?  Why do I care about this?

Ever driven down a country road and the car coming at you has a piercing blue light that is poorly focused and blinds you and you have to hold your hand up to cover it?  Then you have experienced crappy color selection, probably along with a poorly done HID conversion.

Some example temperatures:

  • 2,800K - 100W Incandescent Light
  • 3,000K - 100W Halogen Light
  • 4,800K - Direct Sunlight
  • 5,000K - Common modern LED OEM lights in cars

There seems to be a fair bit of research out there that indicates that at least for urban environments, lighting between 3000K and 5000K provides the best visibility.  Most places seem to recommend 4000K.

But remember that we’re talking about human perception, and the eye has pupils that need to dilate as well as two different systems to detect light (rods and cones.)  Red/yellow light allows your pupils to dilate more, which are found in the lower color temperature range.  It takes a lot longer for your eyes to adapt to darkness than they do for that dark adaptation to be destroyed.  And the brighter and whiter the light, the faster dark adaptation can be destroyed.  So the lower the temp, the better for the driver.

So when looking at lights, use something below 5000K.  Stick with 4000K if you can find them, and even 3000K if you can generate enough light at that temperature.  Temperatures above 5k will blind other drivers and hurt their night vision, and affect the driver’s vision as well.  Preserving night vision with good light temperatures is just as useful as adding more light from a driver’s perspective.

Side note: if you’re going to add lighting to the inside of the car to help with driver changes, consider using a red interior light.  Red light doesn’t take away night vision like a normal white light does.  You can do this with either a red bulb/LED or with a red filter.

Lighting Tech

There are a few different kinds of types of lights for cars, so you’ll need to figure out what you need to use.

Incandescent: Old school tech.  High power requirements, low output.  Low color temps.  But they work.  Generally if you have a sealed beam like this you can replace it with a Halogen version at very low cost from a normal OEM supplier and it will be much better.

Halogen: Probably one of the best lights if you want to have an easy solution in the aftermarket.  High power requirements, good output.  Low color temps.  If you want to run many of these, you will need to worry about your power budget since they draw a lot of power.

HID: Can be excellent, if OEM.  Brighter than Halogen, with lower power requirements.  Higher color temps, though, often past 5k.  Beware of HID conversion kits:  A conversion kit to HID that doesn’t include a change to the reflector behind the lamp will often spill light all over the place and can be just as bad as a crappy LED.  Don’t assume that an HID conversion will be an improvement.  They usually aren’t.  All that extra light is wasted and ends up in other drivers’ eyes.

LED:  A high-quality LED light can have very low power requirements, be very bright, and are available in a range of color temperatures.  However, a good LED light that will pass tech will be 10x the cost of an equivalent halogen.  If your LED light seems like a good deal, it’s probably crap and will spill light everywhere.  Anything designed for “offroad use” is also probably crap since they are likely to have the wrong beam type.

Power Budget

Once you’ve picked lighting tech, you need to figure out how much power you have.  Most alternators run from 50-80A by default, but you should check your specific alternator.  Alternators that support more than this are also available.  Remember that Watts = Volts * Amps.  Some lights list watts, some list amps.  You’ll need to convert.  And direct measurement is often the best way of verifying if a claim is true.

If you want to run four halogens, they can pull a lot of power.  And you still need running lights, brake lights, your fan (can be huge), and the engine’s electrical.  Sit down and do the math.

Connectors

If you’re doing aftermarket, there are several different kinds of connectors.  Look at the connector type you’ll need to use listed with the car.  Many sealed beam halogens use the same connector, and they are easily available.

HID is more complex than other systems, and often require a ballast system that is powered separately.  They will have their own connector setup.

LEDs can come with a variety of connectors.

Mounting

If you’re doing your own mounts, consider making sure that the mounts include at least one triangle.  Putting two mounts in the same plane will cause the lights to vibrate, often making it difficult to see.  Also think about how to replace a light if it breaks.

Rubber spacers can also help with both vibration and reliability.

And think about setting up your mounting so that the lights are roughly aimed properly to start with.  You can follow the aiming instructions again before installing your mounts.

Reliability

It turns out that race cars kick up a lot of stones, tire chum, and other FOD.  There are three aspects to this:

  1. The lights need to be strong enough to handle being hit by debris.  A lot of aftermarket lights actually aren’t good at this.  OEM lights are strong enough to put up with this since they are usually made from very thick glass or plastic.  (In the author’s personal experience three out of four hella 500 lights were smashed during the daylight hours of a 24 hour race and had to be replaced, even though they were covered with plastic covers.)
  2. Collision damage.  You hit people or get hit sometimes.  Consider putting your lights behind your front bumpers so they aren’t the crash zone.  Reminder that the rules state that you can’t put the lights higher than the OEM location.
  3. Electrical failure.  Put relays and high power fuses inline and control them with a high-quality switch.  Consider wiring each light separately in case one component fails leaving you blind on track.  This is a safety thing.  And think about what happens when it rains.