Sunglasses and Driving: Which Ones Are Banned and Why?

The General Directorate of Traffic (DGT) has established clear regulations on the use of sunglasses while driving, not only as a matter of comfort, but also for road safety.

According to the General Regulations for Drivers, drivers must have the minimum visual acuity specified in Annex IV when driving. The regulation authorizes driving with binocular visual acuity of 0.5 (with or without correction); however, drivers must be instructed that they must drive with the best vision they can achieve, and if they achieve vision better than 0.5 with glasses or contact lenses, even if they are not required to, they must wear them.

Visual acuity (the definition or detail with which objects are perceived), the visual field (the total space covered by vision when looking at a central point) and contrast sensitivity (the ability to distinguish an object from its background) are basic driving abilities that can be altered by numerous diseases or disorders of the organ of vision (such as cataracts or glaucoma) or refractive disorders (such as myopia or astigmatism).

Vision problems can also arise when there are problems in other organs or systems, as occurs, for example, with diabetes.

The intense summer sunlight can impair our vision while driving. During this time, many of us turn to sunglasses to regain comfort in the harsh sun and to protect our eyes from solar radiation—especially ultraviolet radiation—that can damage them. Those who need prescription lenses for driving should be reminded that if they wish to wear sunglasses, they must also be prescription lenses.

The DGT's first and most important recommendation is that sunglasses be approved, meaning they bear the EEC seal guaranteeing their compliance with safety standards. The European Automobile Commission (CEA) emphasizes that purchasing them from opticians or specialized establishments is the best way to ensure their reliability.

According to CEA, choosing the right glasses is vital to avoiding significant road risks and avoiding fines.

The DGT classifies sunglasses into five categories based on their ability to block light, with category 4 being the only one completely prohibited for any type of driving. These sunglasses, designed for extreme light conditions such as high mountains, absorb up to 98% of light, drastically reducing visibility and making them a hazard while driving.

Furthermore, the use of any category of sunglasses, from 0 to 3, is prohibited at night. Categories 2 and 3, which absorb 81% and 92% of sunlight respectively, are permitted for daytime driving, but nighttime use is punishable by a fine due to the significant reduction in visibility.

Failure to comply with this regulation can have serious consequences. The DGT penalizes the use of category 4 glasses while driving with a fine of 200 euros. The same penalty applies to those who drive at night wearing sunglasses, regardless of their category. CEA emphasizes that the main objective of these measures is to guarantee road safety, preventing drivers from putting their lives and the lives of others at risk.

In a presentation entitled "Sunglasses. What is the most appropriate protection for each person?" presented at the Glasses and Lenses Forum, Professor Amalia Lorente, from the Faculty of Optics and Optometry at the Complutense University, stated that "when we wear sunglasses, the pupil opens and visual acuity decreases. If we are also ametropic, we will see much worse, because contrast and sharpness are lost." This is why it is highly advisable for those with visual impairments to wear prescription sunglasses while driving.

The aforementioned professor analyzed what aspects professionals should consider when advising their clients on the most appropriate sunglasses. Her advice was to know what the sunglasses will be used for and where they will be using them.

"Outdoors," explains Amalia Lorente, "luminance (the amount of energy or brightness reflected by an object) increases dramatically. But a street in New York, with tall buildings, is not the same as one in Torrelodones, with chalets and low houses." Based on this luminance, a specialist can determine the transmittance (the amount of energy the lens lets through) or the filter that a person needs in their sunglasses. In fact, based on these factors, the optician will recommend a filter between 1 and 3 for daytime driving. She also reminded everyone that "a category 4 filter (reserved for winter sports) should never be used while driving."

Regarding the color of the lenses, the professor at the Complutense University generally recommends using gray, brown, or green filters "that do not alter color perception," noting that brown filters "increase contrast" and green filters, "in addition to increasing contrast, reduce reflections and eye fatigue."

Rose-tinted lenses also increase contrast and reduce eye fatigue during prolonged use, while yellow lenses, because they block blue light, may be advisable for patients with retinal pathologies. The expert states that "there is no scientific evidence that a particular lens color improves vision in certain types of ametropia. There is a sensation of greater brightness, but it does not improve detail or produce greater acuity," and attributes the comfort reported by some patients to the individual's neural processing.