How To Test Blue Light Filters

How To Test Blue Light Filters

The use of blue light filters is gaining more and more traction as people continue to discover their merits. Blue light filters help reduce strain on the eyes and also ensure our sleep cycles run smoothly. They come in many different forms including software like f.lux and physical blue light filters like screen protectors and protective eyewear. While blue light filters are easily accessible, it’s imperative that you find out if the product actually works. And how do you do that? By testing the blue light filters.

It’s unfortunate that there are some unscrupulous retailers out there who may sell ineffective filters banking on the fact that many buyers just take their word for it. There’s also a huge amount of blue filters online all claiming to block, filter, or reduce blue light. Without a set criteria for comparison, determining the effectiveness of any blue filter you come across can be a daunting task. However, there’s a way for you to conveniently test your blue light filter and find out how effective it is in protecting your eyes. Here’s how to test blue light filters.

How to test physical blue light filters

These are the solutions to those who seriously want to reduce their exposure to harmful blue light and not just reduce glare on their devices. As mentioned previously, physical blue light filters come in many forms like glasses and screen protectors. Whatever the choice, determining the effectiveness of your blue light filter begins even before you make your purchase. Before buying your filter, ensure you request the transmitters spectrum of the product from the retailer. This is a graph that illustrates the percentage of light passing through the blue light filter, according to wavelength.

Most high-energy blue light is found between wavelengths 380nm and 470nm. Some filters will filter out all the blue light below 400nm, others below 480nm and the really effective ones will block all the blue light below 520nm. The trick to it is finding a balance and getting a filter that blocks just enough blue light as it still has its uses, especially during the day. Those that block more blue light will cause more colour distortion while those filtering less blue light will seem clearer. So if you want glasses that won’t hinder tasks requiring maximum vision like driving, then settle for those that filter less blue light (e.g. below 400nm). On the other hand, those who want to completely get rid of blue light exposure at the end of the day are better off with glasses that filter more blue light (e.g. 530nm and less)

After you buy your blue light filters, you can still test how good they are at what they do. You can do that by comparing the colour spectra in the two bars below.

colour spectrum chart to test effectiveness on physical blue light filters ie screen protectors or glasses

Source: wikimedia

If your colour perception is top-notch and your monitor shows the full-colour range (red-blue-green), then the two bars should appear to be different. The upper bar represents the normal visual colour spectrum while the lower bar is a colour spectrum where the blue has been removed by photo editing software. As you can see in the lower spectrum, the blue component has completely vanished.

If you have a powerful authentic blue light filter filtering out more than 90% of blue light, then the two spectra should look completely identical. This is because the filter manually accomplishes what was done to the lower spectrum by extracting all the blue light. For weaker blue light filters, the two bars won’t be identical as you’ll still be able to see some blue or violet hues in the upper spectrum.

Updated: 26/02/20

Please note, this method of testing is now inadequate due to different types of display screens, LED, OLED, LCD etc and the variability of products. The best way to know the amount of blue light filtered is to look at the spectral transmittance graph of the blue light filtering product and how much light is let through. Please see our data below.

Blue light transmittance graph for iphone and ipad

Blue light transmittance graph for blue light filter for pc


Blue light transmittance graph for blue blocking glasses

Testing blue light filtering software

When it comes to software, then it’s probably a good idea to find the best. The most popular blue light filters with the most favourable reviews are more likely to be suitable. Such applications include f.lux, Night Light, and Night Shift for laptops as well as Midnight, Twilight and Dimly for phones. All these apps directly help reduce that amount of blue light released by a monitor.

Macstation Min

If you want to test the blue light filtering software you choose for your device, the process is surprisingly similar to how you would test physical blue light filters. You also compare two different colour spectra.

colour spectrum chart to test effectiveness on software based blue light filters ie downloadable software

Once again, if your screen displays the normal colour range and you aren’t colour-blind, then the two images above should be different. The left image represents the normal colour spectrum while the right one is a colour range where the blue component has been diminished using photo editing software. While viewing the above image, activate your blue light filtering software. At the highest setting, the two images will appear to be identical. As you reduce the amount of blue light being filtered, you’ll notice that the blue colour on the left image stands out.

So if you aren’t sure how much blue light is being filtered, don’t hesitate to test your blue light filter right now. You can also find out more about blue light filters and What is Blue Light? at



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Current Version
July 21, 2023

Written By

Dhruvin Patel | BSc Hons, MCOptom, Optometrist

Edited By

Omba Kumwenda | BA, MEng

Medically Reviewed By

Asad Hamir | BSc Hons, Optometrist

Copy Edited By

Tara Tadlock | MA

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