Blue light blocking glasses are marketed as a shield against the high-energy visible light emitted by digital screens, aiming to alleviate eye strain and support healthy sleep cycles. Consumers often purchase these lenses hoping for genuine protection, but skepticism about their effectiveness is widespread. Knowing if your glasses are filtering blue light as claimed requires practical verification. This article details several at-home methods you can use to determine if your blue light glasses are working.
How Blue Light Blocking Technology Works
Blue light blocking glasses employ two main methods to filter out a portion of the high-energy blue-violet light spectrum, which ranges from approximately 400 to 450 nanometers. The first method involves a specialized coating applied to the lens surface, which works by reflecting the blue light away from the eye. This reflective coating often produces a noticeable blue or purple sheen when viewed at an angle against a light source.
The second common approach uses embedded pigments within the lens material itself, causing the lens to absorb blue light as it passes through. These lenses typically present with a subtle yellow or amber tint, which becomes more pronounced as the percentage of blocked blue light increases. Clear lenses generally rely on the reflective coating and tend to block a lower percentage of blue light, often around 25% to 30%, while tinted lenses can block significantly more.
Performing the Dedicated Pen Light Test
Many blue light glasses are sold alongside a specialized testing kit that includes a small, high-intensity light source and a test card, often marketed as a blue light pen or laser. The card contains a treated section that changes color when exposed to blue light. To perform the test, shine the light directly onto the treated white card without the glasses in the way; this should result in a distinct blue or purple spot appearing on the card.
Next, hold one lens of the glasses directly over the treated area of the card, ensuring the light beam must pass through the lens. If the glasses are effectively blocking the light, the spot on the card should either remain white or show only a minimal change in color. If the blue spot appears as clearly and intensely as it did without the glasses, the lens is not blocking the light source’s specific wavelength. You can also shine the light through the lens and compare the resulting spot to one created by shining the light around the lens to visually gauge the reduction in intensity.
Many of these blue light pens actually emit violet light (380–400 nanometers) rather than the higher-energy blue light (400–500 nanometers) that screens predominantly emit. Therefore, while passing this test indicates the glasses block violet light, it does not guarantee they filter the full range of blue light wavelengths. This test is better viewed as a quick verification of the coating’s presence.
Simple Visual Checks Using Digital Screens
You can conduct several qualitative checks at home without needing any specialized equipment by using a bright digital screen, such as a computer monitor or smartphone displaying a white background. The Color Shift Test involves putting on the glasses and observing a blank white screen, such as a word document. If the lenses contain the yellow- or amber-pigmented technology, the white background should take on a noticeably warmer, yellowish hue. This color shift confirms that the glasses are absorbing a portion of the blue light that contributes to the white color.
The Reflection Test is useful for checking glasses that claim to have a reflective coating. Hold the glasses up to a bright light source, such as an overhead lamp or a window, and examine the reflection visible on the outer surface of the lens. A working reflective coating will typically show a distinct blue or purple reflection on the lens surface, indicating the lens is actively bouncing a specific portion of the light spectrum away from your eye.
Understanding Test Reliability and Limitations
While at-home tests provide a good initial indication, their reliability is not absolute, and they have several limitations. The primary issue is that most consumer-grade tests, including the pen light method, only check for filtering within a very narrow band of the visible light spectrum. A lens might successfully block the specific violet wavelength of the test pen but allow a significant amount of blue light from a screen (420–450 nm) to pass through.
The percentage of blue light blocked varies widely, from around 20% in clear lenses to nearly 100% in deep amber or red lenses. A lens may pass a visual test by blocking only 30% of the blue light, which is sufficient to produce a noticeable color shift, but it might not be enough to affect your sleep cycle if used late at night. The subjective nature of the screen and reflection tests also means that one user’s perception of a “warmer tone” or a “blue sheen” might differ from another’s. The only reliable way to measure the exact percentage of blue light blocked across the entire spectrum is through a professional spectrophotometer test.