How to test blue light blocking glasses?

How to test blue light blocking glasses?

Science continues to discover the harm caused by chronic exposure to blue light. Through consistent contact with televisions, smartphones, computer screens, eReaders, and LED lights, the damage mounts, accumulating with every moment.

Dry eyes, inflammation, cataracts and visual damage. Trouble falling asleep, increased wakefulness, insomnia. Oxidative stress that hastens the aging process. Our non-stop exposure to blue light subtly chips away at our wellbeing.

Because of these discoveries, the market has taken note. Companies, like ours, have invested heavily in the development of proven products designed to protect human health. However, as with any invention, there are fraudulent businesses prepared to take advantage as people seek to safeguard themselves and their loved ones.

Being able to assess whether a product does what it says on the box, so to speak, then becomes crucial.

In this article, we’ll discuss how to determine whether your glasses are up to spec, and dispel a common myth.

First, let’s look at how to determine whether your blue light blocking glasses do, in fact, block blue light: spectral transmittance graphs.

How to use the spectral transmittance graph to assess the quality of blue light blocking glasses?

Normal glasses don’t block blue light. Prescriptive eyewear is designed to correct eye problems and enhance vision, not to filter colour from the visible spectrum. To screen blue light from your field of view requires special lenses.

But while many products claim to block this hue, few do. This is where assurance and assessments are needed.

Prior to purchasing your blue light filtering glasses, request the product’s spectral transmittance graph from the retailer. This graph shows you how much blue light is filtered out.

Ocushield has three spectral transmittance graphs. One for our smartphone and tablet screen protectors. Another for the laptop, monitor and PC filters. The third is for our blue light blocking glasses. These reveal how much blue light our products block; it’s slightly different for each product.

The blue light that is most harmful to the eyes, both short-term (eye strain and headaches) and long-term (eye diseases such as macular degeneration) is found between 370-455nm. This is the range that a filter should, therefore, focus on blocking.


When blue light is removed entirely, the appearance of a digital screen changes markedly. This can make it difficult to view. If your glasses are not fit for purpose — if they do not limit the most harmful rays while being user friendly — they will sit on your desk unused. There, they offer no protection.

Testing shows that our glasses filter out up to 99% of the wavelengths below 400 nm, and up to 40% of harmful blue light between 401 - 460 nm. They protect against the most dangerous rays while permitting a comfortable, usable screen.

Note: If a product’s spectral transmittance graph reveals less than 30% of up to 455 nm blue light is blocked, leave them in the shop. They do not provide the level of protection you need and are a waste of your money.

Myth: The blue light blocking test that sounds logical, but doesn’t work.

I’ve noticed a common misconception online that needs to be addressed. It sounds logical, but sadly is not evidence-based; it is simply not true.

The myth is based on an image similar to the one below where R = red, G = green, B = blue (obviously). It states that, assuming you are not colour blind and there is no filter currently on your digital screen, these colours will look true to life.

When you place your blue light blocking glasses on and look again, you will notice the B section changes from blue towards black. This, in theory, indicates blue light is being stopped, just as the glasses are meant to do.

If the colour remains sharp and vibrant, if the blue remains distinctly blue, the wavelengths emitted from the screen are thought to remain unfiltered. In this case, the misconception assumes that the constancy of the image means a product’s claims do no match the end result: They do not block blue light.

However, while sounding logical, the longest and safer wavelengths of blue light that fall between 470-500 nm will still show. As such, blue light will be present - because we're not stopping all blue - just the bad stuff!

The only way to accurately assess the power of a blue light filter is an official spectrometer report from a lab that provides a third-party result. No other manual test or gimmicky blue light card test can do the job. Why choose Ocushield for your blue light blocking glasses? At Ocushield, we understand that purchasing a pair of blue light blocking glasses is an important step. We also know that there are a range of possible options available and the decision may be difficult, even confusing. That’s one of the important reasons why we share our spectral transmittance graphs freely on our site. You can view them here. Additionally, our products have been developed, designed, and tested by leading Optometrists in the UK. Our blue light filter is registered with the medical body MHRA, which is a world leading regulatory body. We have the expertise and experience, the technology and the training that ensures our glasses work. The use of blue light blocking technology in our modern, digital age is a crucial, protective step. Spectral transmittance graphs ensure you receive products that protect your health, now and into the future.

1 comment

  • Venomlily16

    Thanks for letting us know . I recently got a pair of blue light computer glasses as a birthday present and after using them, I couldn’t tell if they were helping or not . I figured maybe this was like a modern-day “Emperor’s New Clothes” concept where we were ALL being fooled into buying stylish, but useless glasses . I can’t believe I almost fell for the primary color circles thing .

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