Most states have laws designating which colors you may use for fog lights. In general, white, amber, or yellow fog lights are legal across the United States. Although fog lights manufacturers use other colors, such as purple, red, or blue, these lights are harsher on the human eye and can be hazardous.
For this reason, these dangerous fog light colors are illegal in many states. Check your state laws to find what is legal in your area. However, be aware that even if they are legal in your state, they may be illegal in other states, which may be a problem if traveling from state to state.
Research and experience have found that yellow fog lights illuminate better in foggy conditions than white lights. Experts say that yellow penetrates further than white lights because of the longer wavelength, leading to better visibility. In addition the light scatters less so it does not illuminate the fog and rain up higher in your field of view.
Therefore, compared to white, yellow fog lights don’t glare as much and make it easier to see with your lights on. Decreased glare causes less eye fatigue which is especially important when driving with dangerous road conditions.
Although you’ll find many benefits to yellow light, white lights are brighter than yellow ones. However, brightness may not factor in as an advantage in every situation. Therefore, the many benefits of yellow lights vastly outnumber this one disadvantage.
