blue light

Blue light is the part of the visible light spectrum with the shortest wavelengths and the highest energy. It lies roughly between 380 and 500 nanometres and is also known as HEV light, short for high-energy visible light. Blue light is found in natural sunlight, but also in artificial light sources such as LED lighting, smartphones, tablets and computer screens.

Because blue light has a short wavelength, it scatters more easily in the eye than light with longer wavelengths. This can contribute to visual fatigue during prolonged screen use. In addition, blue light plays a role in regulating your day-night rhythm: exposure to blue light during the day can help you stay awake, whilst exposure in the evening can disrupt your sleep-wake cycle.

Lenses with a blue light filter contain a coating or pigment that absorbs or reflects some of the blue light. The amount of light filtered varies by manufacturer and type of lens. Some lenses mainly filter the range around 400 to 450 nanometres, whilst others cover a broader spectrum. The lenses often have a slightly yellowish or orange tinge, depending on the strength of the filter.

When is a blue light filter used?

Lenses with a blue light filter are mainly worn by people who spend a lot of time working at a screen or using a smartphone or tablet late at night. The idea is that the filter may help reduce visual fatigue and minimise disruption to sleep patterns, but the scientific evidence for this is still limited and inconclusive.

Difference from other coatings

A blue light filter is different from an anti-reflective coating. An anti-reflective coating reduces glare and reflections on the lens, allowing you to see more clearly and suffer less from glare. A blue light filter specifically targets blocking part of the blue light spectrum. Many modern spectacle lenses combine both: an anti-reflective coating with a built-in blue light filter.

Blue light and contact lenses

There are also contact lenses with a built-in blue light filter, but these are less common than spectacle lenses with this feature. Most people who specifically want to filter out blue light opt for spectacles with coated lenses.

Limitations and nuances

It is worth noting that the majority of the blue light you are exposed to on a daily basis comes from the sun, not from screens. Furthermore, a blue light filter on your glasses only blocks some of the blue light, not all of it. Whether the filter actually helps to reduce eye strain or improve sleep depends on many factors, including your screen time, the brightness of your screen, your posture whilst working and your personal sensitivity.