What is the best Color temperature?

and What value reduces the most Blue light

A lot of users asked me what is the best value of Iris for blue light reduction. Well in this article I’m going to look at exactly this with measurements.

This will be helpfull for users of other software products like f.lux, Redshift, SunsetScreen, Night Shift and Night Light.

The Android Twilight and Night mode use different algorithms than Color temperature. Twilight is like the Iris Overlay mode and Night mode is like the Iris Groot color scheme.

I made a 10 measurements of the display from 6500K to 1200K since this is the format that is universal to all blue blocking softwares and I think is enought.

6500K is screen with no color changes at all. This is perfectly calibrated screen.

1200K is the lowest value of f.lux, Redshift, Night Shift and Night light. Actually Redshift can go down to 1000K, f.lux to 800K, SunsetScreen to 500K and Iris to 0K, but this is irrelevant.

The bellow measurements are the same for all software products. No matter what anyone tells you all this softwares do the same thing with color temperature. They may do it with different algorithms, but the end result is the same.

6500K – 100%

At 6500K this is how the color graph looks like. You see that blue light is even more than all other colors and this is the first reason that this value is bad for your sleep and for your eyes.

We will just use this measurement as comparission to other values and as how normal displays emmit colors.

The height of the blue part of the graph shows the amount of blue light emitted.

The height of the green part of the shows the amount of green light emitted.

The height of the red part of the shows the amount of red light emitted.

It’s important to know that most softwares reduce also the green light at low values and red light is untouched at all values.

Thus to select the best value we will need to select the value with lowest blue light and highest green light, but green light should also be reduced for best eye protection and sleep.

5970K – 90%

Close to the light of Mercury vapor light lamp and Cloudy sky light the color graph looks like this

5440K – 80%

Close to the light of Daylight metal halide lamp (HMI) and Average noon light the color graph looks like this

4910K – 70%

Close to the light of Late morning and Early afternoon light color graph looks like this

4380K – 60%

Close to the light of Cool White Fluorescent lamp (CFL) and Mid Morning and Mid Afternoon light the color graph looks like this

3850K – 50%

Close to the light of Standart Clear metal halide lamp and Later Afternoon light the color graph looks like this

3320K – 40%

Close to the light of Halogen light lamp and Evening light the color graph looks like this

2790K – 30%

Close to the light of Household tungsten light lamp and Sunset light the color graph looks like this

2260K – 20%

Close to the light of High pressure sodium light lamp the color graph looks like this

1730K – 10%

Close to the light of Candle light the color graph looks like this

1200K – 0%

Close to the light of Ember light the color graph looks like this


To save you the thinking here what all these results mean. The lowest blue light will be at 1200K or bellow, but this is actually not the best setting.

At 1200K a lot of the green light is reduced and the screen may be hard to read.

Best value for sleep and blue light reduction is 1900K or Candle light.

Iris is using 3400K for the night and 5000K for the day. The reason for this is because new users get shocked by the big changes to their screen colors and can’t handle the transition from really bright screen to 1900K.

Start with 5000K during the day and 3400K during the night. After several months gradually switch to 1900K all the time for best health.

Try to get more full-spectrum sunlight and go outside from time to time to produce good amounts of melatonin.

Thank you for reading this article,
Daniel – Founder of Iris

22 thoughts on “What is the best Color temperature?

  1. Hi Daniel, i’m using 1900k at the moment during the day & night feeling very comfortable with it. Should i keep using it at this level or use recommended setting ?

    1. Use it at 1900K yes. It’s more healthy
      The default values are not too aggressive because new users don’t feel comfortable lower values like 1900K

  2. Thanks Daniel. I have mine set at 2000 (it’s either 2000 or 1800), but what intensity do you recommend? And what level of screen dim? Does that matter?

    Thank you,

    1. You need to match the Brightness to the room lighting. It’s not about the value it’s more like

      The monitor should not look like a light source in the room. So for example if the lights in the room are ON and it’s night 90% may be good while if the lights are OFF 50% brightness might be good

      The screen should be easily visible and focusable without getting eye strain so the rule of thumb is match Iris brightness to the room lighting 🙂

      CEO Iris

  3. Hi, I was wondering what it the best color theme to have coupled with my color temperature set at 1900(it’s important to note that I’ve been using these settings for a while but I find dark a little hard to read and white is still a little “too in my eyes”.)

    It should be noted that I mostly read text that has different colors(because of code highlighting). What do(es) the developer(s) at iristech use?

    1. I use a dark theme (more like grey) and lighter font color and highlights, you can do that or the reverse, which is white (light) background and darker syntax so that they contrast and you can see better. Also, avoid colors that are blue or close to blue (like purple) because when you remove the blue from them, well they became harder to spot 🙂

  4. thanks a lot Daniel for the research on % charts . I feel really sorry to have missed such a wonderful article so far ! thank you once again !

    1. Hi Im using Twilight app in my mobile. I have setting of 3000k both during Day(mostly under lights at office) and night with Intensity 54% and dim 40%. Is it good? Or should I reduce setting for night?

      1. Hi Arshad, it truly depends on your needs and environment at the time
        If you look at your monitor from afar and it looks like a light source in the room then it’s too bright

  5. why is 1900k best setting ??
    i have mine at 1200k,it looks odd but i have gotten used to it.should i go back to 1900k ??

    and is it okay to have the same color temperature(1200k) at both day and night

    1. 1900k is probably the most optimal resolution, meaning it’s both great for your eyes and it preserves some of the colors

      You can keep usiing 1200k, yes 🙂

  6. Hello Mr.Daniel,
    Is it ok to use 500K screen?
    Also which one is better — Black Letters with White Background (OR) White Letters with Black Background?


    1. I prefer (and think it’s better) to use a dark background rather than a white one (especially at night) because it just gives you less eye strain 🙂

      And yes, it is okay to use your screen at 500K 🙂

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    1. Match the brightness to the room lighting
      The screen shouldn’t look like a light source but like a book matching the room lighting

  9. Im confused, there is suggestions on here to use low as possible during the day from computer monitors, but isnt it best to use 5000k or more during the day and then tapper to 2k evening before bed for circadian rhythm and melatonin production?
    i use 4900k on computer during day in office of fluorescents. in the morning i use 10000 lux light therapy before work. outside at lunch but its not possible 6 months per year especially in Portland Or.

    1. The default settings in Iris during the day is 5000K
      The point is that during the day you don’t need to remove all blue light but it’s good to slightly improve the contrast with 5000K as a color temperature

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