Blue screen
A full screen of pure blue, driving the blue sub-pixel to maximum while red and green stay completely off.
Esc to exit · arrow keys to change · H hides the controls
Dimming changes what is sent to the panel, so this is no longer an exact colour value. Return the slider to 100% before judging anything.
What a blue screen is for
The field where blue faults finally show
Blue contributes only about 0.0722 of perceived luminance in sRGB, which makes it by far the dimmest of the three primaries. That has a practical consequence: a blue element that has failed contributes so little to a white field that you will almost certainly never notice it there. Put the panel on a pure blue field, with red and green switched off, and that same failure becomes an obvious black dot. If you are checking a screen before a return window closes, this is the field people most often skip and most often should not.
Judging blue uniformity and viewing angle
Blue is also the primary where viewing-angle behaviour tends to be most visible. Look at a blue field straight on, then from perhaps thirty degrees off to one side, and watch for the field shifting towards purple or washing out unevenly. VA panels in particular often show a noticeable shift. This is normal panel behaviour rather than a defect, but knowing how your screen behaves off-axis is useful if you share it with anyone or use it for anything colour-critical.
Blue light, honestly
Blue is the part of the visible spectrum most associated with alertness and with disrupted sleep timing, which is why every operating system now ships a warm-light mode. A full blue field at high brightness is an uncomfortable thing to stare at, and there is no reason to. Run the check, look for dark dots, and move on. Brightness and how late you are using the screen matter considerably more than the colour of any single test field.
Checking a compressed video pipeline
Saturated blue on a dark background is where chroma subsampling and aggressive video compression struggle most, because colour information is stored at lower resolution than brightness. If you are testing a streaming box, a long HDMI run or a capture setup, a flat blue field with sharp edges is a useful worst case: blocking, smearing or ragged edges here point at the signal chain rather than the panel.
How to run this test
- Go full screen. Blue is the dimmest primary, so give your eyes a few seconds.
- Look for black dots. These are failed blue elements and they are effectively invisible on any other field.
- While you are here, look at the field from thirty degrees off to one side and note any shift towards purple, which is normal viewing-angle behaviour.
- Finish the set with red and green if you have not already.
What a problem looks like
- Black dots on blue
- A failed blue element. Because blue is so dim, these are effectively invisible on white and on most normal content, so this field is where they are found.
- Purple shift off-axis
- A blue field drifting towards purple or magenta as you move your head is ordinary viewing-angle behaviour, most pronounced on VA panels. It is a characteristic, not a fault.
What to do next
If something looks wrong, check it again in a normally lit room and from straight on, then check whether it appears on a second device. If it only happens on this screen and you are still inside the return window, that is the time to contact the retailer.
Questions people actually ask
Why does a blue screen look dimmer than red or green?
Because it is. Blue accounts for roughly 7 per cent of perceived luminance in sRGB, compared with about 71 per cent for green. Your eye is genuinely less sensitive to blue, so a full blue field looks much darker than a full green one at the same signal level.
Is this the blue screen of death?
No. This is an ordinary web page filling your screen with blue so you can inspect the panel. Press Escape to leave it. A Windows stop error is generated by the operating system and shows text and a QR code.
Should I worry about blue light from this test?
No more than from any other bright screen. Run the check, which takes seconds, and turn the brightness down if it is uncomfortable. Sustained high brightness late at night is the part worth thinking about, not a brief test field.