Frequent Questions

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General Questions

  • What are LEDs?

    Light Emitting Diodes (LEDs) have been around for years in red, yellow and green. New technological advances have given us incredibly bright blue and white versions as well. The rated brightness varies by the actual diode size and how wide the beam angle is.

  • Are LED lights reliable?

    Yes, HDL’s LED lights are very reliable. LED lights provide many benefits over incandescent lamps:

    • They are solid-state devices that do not use a brittle metal filament, susceptible to shock and vibration, like incandescent lamps use.
    • There are no moving parts to break.
    • The sealed designs provide increased durability and reliability.
    • When using LED lights, you will no longer have to worry about bad connections between the bulb and socket due to moisture, dirt and corrosion (which is common to incandescent lamps).
  • LEDs seem to cost so much more, why not just stay with incandescent lights?

    Three reasons:

    • Safety - LEDs provide brighter illumination, and the illuminate much quicker than to incandescent bulbs.

      As soon as you apply the brakes, your LED brake instantly go on at full brightness. This improves safety, and makes your truck, trailer, or RV more visible to other vehicles during stops, and/or when turning.
    • Durability - Most incandescent lights are rated for approximately 3,000 hours, while similar LED products are typically rated for 100,000 hours.

      If you leave an incandescent light on for 24 hours/day, 7 days/week, the light would burn out in less than 5 months. Your LED light will last 11 years under the same conditions.

      Additionally, incandescent bulbs typically last far less then their rated hours, due to road shock, vibration, heat, cold, and moisture. In the end, you replace incandescent lights much more often than similar LED products.
    • Power Consumption - LED lights are extremely energy efficient, and require much less power to operate than incandescent lights. This reduces the load on a vehicle’s electrical system, and drastically minimizes the risk of other electrical components like alternators and batteries failing prematurely.
  • Lumens, candlepower, watts...what do these all mean?
    • Lumens - a measurement of how much light a device produces (brightness). Lumen ratings have become industry standard when measuring brightness.
    • Candlepower - a measurement of how concentrated a device’s beam is (beam shape). Just because a bulb produces more candlepower, doesn't mean it produces more light. Think of a laser pointer; it has a high candlepower (beam), but is not used to light up a room.
    • Watts - how much electricity a light uses. Watts are often confused for lumens. Think of watts as the energy going into the creation of the light that a bulb produces.
  • What does IP Rating refer to?

    IP Rating refers to the degree level of electronic dust and water prevention.

    • The first number refers to dust prevention.
    • The second number refers to moisture prevention.
    • Lower numbers equal lower protection, whereas higher numbers equal higher protection. For example, IP55 carries a lower dust and moisture protection value than a rating of IP67.
  • The light has more LED's so it must be brighter right?

    Once upon a time, using a larger amount of diodes was necessary to get many lights to meet “on highway” compliance rules and regulations. As LED and lens optic technology has evolved, improved components and designs have allowed manufacturers to create new and better products, often times using fewer diodes. In short: more is not necessarily better. On the contrary, less components means there is less to go wrong and is also why the cost to the end user has continued to come down.

Troubleshooting & Technical

  • Do LED Lights require special connectors?

    HDL lights are designed for use as direct replacements with most vehicles:

    • Lights are designed to use industry standard two- and three-pin connectors.
    • Some lights may be prewired and require no special connections at all.
    • Many fleets, owner operators and OEMs have been using LED lights as replacements for incandescent lights, with great success, for years.
  • Why are my lights cracking?

    Most HDL lights are made from polycarbonate (industry standard) plastic, the toughest plastic available, with excellent UV protection properties. However, harsh chemicals or cleaners, such as those used in commercial truck washing, can break these components down over time. We suggest you avoid incompatible materials and chemicals when cleaning near lights.

  • I replaced my incandescent light with an LED light. Why does the new LED flash so fast?

    When using LED lamps to replace incandescent stop/tail/turn lamps on your vehicle, some applications require replacing the turn signal and four-way flasher unit with an electronic-style flasher. This is necessary due to the low power-current draw of the LED light.

    Older vehicles with thermal (mechanical) style flasher units commonly have this problem. This is not a defect of the LED product, but rather the design of your vehicle circuitry.

    Many parts stores offer an electronic flasher for your specific vehicle that can increase resistance and correct this problem.

  • My light doesn't work. How can I tell if it is it the light or the wiring?

    First, use a test light or multi-meter to check for an open or improperly grounded circuit, or for voltage from the vehicle. Lack of vehicle voltage means there is a problem with the vehicle wiring or ground. Another method is to substitute a known good light.

    When mounting LED lamps to trailers, don't rely on the “frame” or “chassis” as a grounding point for lights. Run a dedicated ground wire from the light(s) to the plug that connects the trailer to the tow vehicle. This ensures lights have the absolute best ground connection possible.

    One wire can be used to interconnect the ground wires of all lights. That wire can then be routed to the front of the trailer.

    Your tow vehicle should also have a ground wire running from the trailer plug to the frame of the tow vehicle. Don't rely on the hitch ball and trailer coupler as the only method of supplying a ground connection from the tow vehicle to the trailer.

Lighting Laws & Regulations

  • What lights are required on my vehicle?

    Federal Lighting Equipment Location Requirements can be viewed at the following lighting requirement links:

  • What is FMVSS 108?

    This stands for FEDERAL MOTOR VEHICLE SAFETY STANDARD No. 108, which specifies requirements for original and replacement lamps, reflective devices, and associated equipment.

    The purpose of this standard is to reduce traffic accidents, and injuries or fatalities resulting from traffic accidents by:

    • providing adequate illumination of the roadway;
    • enhancing the public’s ability to see and perceive motor vehicles on the public roads; and;
    • reinforcing the public’s understanding vehicular signals in daylight, darkness, or other conditions of reduced visibility.

    FMVSS 108 applies to:

    • Passenger cars
    • Multipurpose passenger vehicles
    • Trucks
    • Buses
    • Trailers (except pole trailers and trailer converter dollies)
    • Motorcycles

    While states cannot require anything different than what is in “108,” they can add regulations.

    Contact your state department of transportation for special situations.

  • Is “SAE” or “DOT” lettering required on lights?

    No lettering is required by NHTSA (108) except for headlights and conspicuity tape.

    The Federal Motor Carrier Safety manual mentions some lights should be marked “SAE,” but this is not enforced.

    HDL marks all lights with “SAE” and/or “DOT.”

    We keep test reports of independent industrial testing on file. They are available by request.

  • What is CMVSS 108?

    CANADIAN MOTOR VEHICLE SAFETY STANDARD No. 108, which is Canada’s equivalent to the US FMVSS 108 standards, with a few small differences.

  • I am replacing OEM STT lights that have reflective lenses. Do replacement lamps need to have reflectors as well?

    The short answer is Yes.

    If you are replacing stop/turn/tail lights on your trailer or vehicle, and the original lights have a reflector integrated into their lenses, federal laws regarding vehicle lighting require that your vehicle or trailer have auxiliary reflectors, or some type of reflective material or tape attached to the sides and rear of your vehicle or trailer.

    See the lighting requirement links listed above. Check your state or local vehicle regulations to determine what the requirements are for reflectors.

*The above FAQs include information which is publicly available from NHTSA(http://, DOT Docket ( and various other public internet websites.

The information is reformatted into plain language without alteration of content or intent. This site is not affiliated with any Federal, State, or Local organization. Information supplied should not be used to determine the legality of motor vehicle equipment in accordance with Federal laws.

The intent of this information is to educate Law Enforcement Officers and consumers as to the safety and legal implications of lighting products with the Federal laws.

For the most current rules and regulations you should contact federal, state and local agencies as necessary.

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