• A motorcycle with its headlight turned on is more visible to others.Ryan McVay/Digital Vision/Getty Images
  
  Motorcycle headlight laws vary from state to state although all states require the use of headlights from dusk until dawn. All states also have laws that govern the brightness of the light. Federal laws take prominence over state laws, which make it easier for motorcycle drivers to travel from state to state and not worry about breaking the law. According to the National Highway Traffic Safety Administration, "Headlight modulators, which cause the light to alternate between a higher and a lower intensity during the day, also increase conspicuity." Federal laws S7.9.4 through S7.9.4.2 are about the use of motorcycle headlight modulators.
  
  

S7.9.4.1

• This federal law states that motorcyclists can use upper or lower beam modulators to decrease the intensity of the light. Subparts of S7.9.4.1 include the following: modulators cannot lower the intensity below 17 percent of the maximum power of the light and the switch for the modulator must be wired into the beam filaments power lead. The headlight must be able to work at full power when the modulation system is not active.
  
  

S7.9.4.2 (a)

• Modulators that are added to the motorcycle as after-market accessories must have a label stating the maximum and minimum wattage. After-market modulators must also comply with all subsections of federal law S7.9.4.1.
  
  

S7.9.4.3 (b)

• After-market modulators must include instructions and a diagram for mounting the modulator's sensor. These instructions must include placement on the motorcycle, orientation of the light and distance from the ground.