#FF0000, red by itself with nothing mixed in. The red sub-pixels supply about 21 percent of a white field's output, so a full red field is far dimmer than a white one.
The page's own dimmer, not your device's brightness.
This red screen test fills your display with pure red, #FF0000, in one press. On red a faulty sub-pixel shows as a black, yellow or magenta dot, and the darker reds make a dim light for a dark room.
Read the full guide
Check a full red screen for dots
1. Press Go full screen on pure red.
2. Scan the field in strips for a dot of another color.
3. Black is a red sub-pixel that stays off, yellow a green one stuck on, magenta a blue one.
What each red color screen is for
Pure red, dark red and maroon light the red sub-pixels alone, at levels 255, 139 and 128: use those for pixel checks and as a dim light. Tomato, salmon, light coral, crimson and firebrick mix in green and blue: reds for a background. Dimmer darkens whichever is on show.
For a red light in the dark, pick maroon, then lower Dimmer and the device's own brightness.
Questions and answers
What is a red screen test for?
It shows the red sub-pixels working alone. A red sub-pixel that stays off is a black dot on red, and a faint shape left by a still picture is easier to see on a flat color like this.
Is a red screen a sign of a fault?
Not here. This page shows red on purpose, as a plain color field for checking pixels and for use as a light. A screen that turns red by itself is a different matter, and no web page can find its cause.
Why use a red light screen in the dark?
The rod cells the eye relies on in the dark are insensitive to long, red wavelengths. Dim red light lets people read instruments while their eyes stay adapted to the dark, which is why cockpits and ships' bridges use it at night.
How bright is a bright red screen?
Pure red, #FF0000, is red at full strength, yet it gives only about 21 percent of the light of pure white: one sub-pixel in three is lit. Green carries most of a screen's brightness, about 72 percent, and blue about 7.
Does a red LED light screen need a special display?
No. The page draws a plain, solid red, blank from edge to edge, and any screen that shows it gives off red light. Pick pure red for a strong glow or maroon for a faint one.
All 14 shades and uses
Reds, from pure red to maroon 8
Pure red#FF0000, red by itself with nothing mixed in. The red sub-pixels supply about 21 percent of a white field's output, so a full red field is far dimmer than a white one.
Tomato#FF6347: the red of a ripe tomato, leaning orange, with green sitting at 99 and blue at 71. Those two partly lit sub-pixels lift it to about 31 percent of white's light.
Salmon#FA8072: a soft pink-red with all three sub-pixels lit, at about 37 percent of white's light, the brightest shade here. A gentle wash for a face or a product.
Light coral#F08080: a muted, slightly pink red at about 36 percent of white's light. Green and blue sit at the same level, so it stays red without leaning orange.
Crimson#DC143C: a deep red with a touch of blue, at about 16 percent of white's light. Cooler than pure red, and a strong color for a sign or a backdrop.
Firebrick#B22222: a brick red at about 11 percent of white's light. Dark enough to sit behind a bright object without throwing much red light onto it.
Dark red#8B0000: red alone at level 139 of 255, about 5.5 percent of white's light. With the dimmer down it makes a red glow that barely lights a dark room.
Maroon#800000: red alone at level 128 of 255. Half the signal gives about 4.6 percent of white's light, the dimmest shade here before the dimmer is touched.
Show all 14 shades and uses (6 more)
Checking the screen on red 2
Which sub-pixel a dot on red isGo by the dot's color. Black means the red sub-pixel there is unlit. Yellow means its green neighbor glows when it should not and mixes with the red around it. Magenta, a pinkish dot, means the blue neighbor glows. White means both neighbors glow.
A faint shape that shows on redA faint outline left by a bar or a logo that sat still for a long time shows best on a flat color, and on some screens on one color more than another. Step from red to the white screen and the black screen and see whether it stays.
As a dim red light or a sign 4
A dim red light for reading in the darkPick dark red or maroon, lower Dimmer and turn the device's own brightness down. The cells the eye uses in the dark respond little to red light, which is why cockpits and ships' bridges are lit dim red at night.
Reading a star chart or a camera dialHold a phone showing maroon over the chart or the dial as a red flashlight. The page's dimmer stops at 10 percent, so use the device's brightness control for the last step down.
How dim the reds goPure red gives about 21 percent of white's light, dark red about 5.5 and maroon about 4.6. Dimmer then scales the color on show toward black, down to 10 percent, and the light figure under the field follows it.
A recording sign on a spare screenA full-screen red on a second monitor or an old tablet by the door reads from across a room as a busy or recording sign. The share link reopens the same red. The screen still sleeps on the device's own timer.
How this list was compiled: Shades, checks and uses chosen and written for this page. Every hex value is a CSS named color, taken from the table of named colors at https://developer.mozilla.org/en-US/docs/Web/CSS/Reference/Values/named-color, read 2026-10-02. The share of light printed for each shade is its relative luminance (0.2126 R + 0.7152 G + 0.0722 B on linear values, pure white as 100), worked out from the formulas at https://en.wikipedia.org/wiki/SRGB, read 2026-10-02. That a pixel is made of three sub-pixels, that a dark dot is one that stays off and a stuck sub-pixel one that stays lit, is from https://en.wikipedia.org/wiki/Defective_pixel; that red and green light make yellow, red and blue magenta, green and blue cyan, and all three white, is from https://en.wikipedia.org/wiki/RGB_color_model; both read 2026-10-02. That rod cells are insensitive to long wavelengths, and that dim red light is used in aircraft cockpits and on ships at night so that eyes stay adapted to the dark, is from https://en.wikipedia.org/wiki/Adaptation_(eye), read 2026-10-02. That a picture left still for a long time can leave a ghost of itself, and that the red, green and blue of some screens wear at different rates, is from https://en.wikipedia.org/wiki/Screen_burn-in, read 2026-10-02. A color on a screen is not a match for paint, print or another screen, and nothing here is a measurement. Licence: own work