Melanopic Ratio, a simple way to test your screenshots and pictures

Did you know that movies can make just 1/10 as much light as white webpages?

We’ve been getting asked a lot recently about how different content affects how bright a screen is. For instance, browsing reddit might make you see ten times as much light as watching a movie, because reddit uses a white page, while movies are a lot darker. You might also wonder exactly how dark your favorite “dark mode” UI is.

You can now just make a screenshot and drag it to this page to find out. You can even drag in 1000 images at the same time. (Since it doesn’t upload to our server we won’t be upset, but your browser might get slow.)

The special thing here is that we’re showing the melanopic response, which lets you see how the picture you provide reduces the eye’s “blue light” response that tells our brains whether it’s night or day. So a red picture will look very dark to those cells in your eye, but a picture of the sky will be pretty bright.

If you do something cool with this, send a screenshot to @justgetflux.

How dark is your screenshot? Just drag and drop images here, or click.

This won't send your files to a server—it's all in your browser.


Details and metrics used

What does the “darkness score” mean?

When we measure circadian responses, we like to use a logarithmic scale, because that’s how the body works. The eye responds over many orders of magnitude, almost three “tens” if you’re counting. So that means to get from “day” to “night” you have to change the irradiance by more than a hundred times—more than most people think is required. When we talk about non-visual responses, it would be a lot better if everyone would talk about factors of 10 and 100 and 1000. These examples would mean a change of 1, 2, and 3 log10 units.

If you only change things by 20% (which some people do), you’re only making a change of 0.097 log units, which isn’t very much. This is why we made our bold darkness metric use this logarithmic number.

A score of 1.0 means the picture is 10% as bright as a white screen, and a score of 2.0 is just 1% of it.

What is Melanopic? Photopic?

Photopic light is based on how bright different colors appear, using a “luminosity” weighting. The melanopic weighting is more blue-sensitive, and it will account for the response of melanopsin in your eye.

What is the M/P ratio?

This is the ratio of melanopic to photopic light in the image. So a “blue” image will have a ratio bigger than 1.0, and an “warm” image will be less than 1.0. So this will give you a sense if the colors in the image or the brightness is having a bigger effect on the result.

Thanks for reading!

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