DeviceBenchFree white field, 3400–7500 K
White screen you can tune to the room
Every subpixel goes to full output and the panel becomes a flat, evenly lit rectangle with no hotspot on it — a 27-inch screen at 400 cd/m² is about 250 lumens spread over 0.201 m², which is a usable light for a face on a video call. Four emission colors between 3400 K and 7500 K let the screen agree with the lamps already in the room, and the slider moves the sRGB code value while telling you what that does to the light, because the curve is 2.2 and 60% of the code range is nearer a third of the brightness than half. Against that sheet, dust, finger grease and a panel whose white has drifted warm all stop hiding.
- 100% free
- No signup
- 3400–7500 K
- sRGB value shown
- No hotspot
Full output on all three subpixels. The brightest setting a screen has, and the one that shows dust.
#FFFFFF — sRGB 255 of 255, which emits about 100% of the light this preset gives at full. Your monitor’s own backlight control is the other half of the answer and no web page can reach it.
Full screen is unavailable in this browser — Safari on iPhone and iPad never grants it to a page. What opens instead is a panel pinned over the whole viewport, so you lose the address bar and the tab strip but not the status bar at the top.
How to use the screen as a light
The first step is the one that decides whether the light helps or hurts.
Choose the light the room already has
Daylight at 6500 K if you are sitting near a window, warm at 3400 K under a yellow bulb, neutral 5000 K when the room has both. This is the step people skip, and it is the one that decides whether the light helps: a camera balances for the average of what it sees, so a screen that disagrees with the lamps behind you pushes your face toward the opposite color.
Fill the screen and set the level while you watch the result
The control bar stays along the bottom edge rather than fading, because a fill light is adjusted while you look at what it is doing to you. Arrow keys move the level in five-point steps if the slider is fiddly, and the readout shows both the sRGB value and the share of the panel's output it corresponds to.
For dust, smears and yellowing, go back to 6500 K at full
A flat sheet at maximum output is what makes surface dirt visible, and it is worth looking from an angle as well as head-on — grease films show up in reflection long before they show up straight on. This is also the setting that exposes a panel whose white has drifted warm with age, which is easiest to spot with a sheet of printer paper held next to the screen for comparison.
Technical specifications
| Emission colors | Four — 3400 K #FFBE87, 5000 K #FFE4CE, 6500 K #FFFFFF, 7500 K #E6EBFF, from the standard blackbody approximation rounded to 8-bit sRGB |
|---|---|
| Why 6500 K is plain white | sRGB fixes its own white point at D65, so a panel showing full output is already daylight-balanced by definition |
| Level range | 20% to 100% of the code range in 5-point steps — sRGB 51 at the bottom, 255 at the top |
| Code value versus light | The encoding curve is about 2.2, so sRGB 153 emits near 33% and sRGB 128 near 22%; both numbers are shown live |
| Light output | Luminance × area × π — a 27-inch 16:9 panel is 0.201 m², so 400 cd/m² gives roughly 250 lumens |
| Out of reach | The backlight itself. Every control here works in the image, above the panel's own brightness setting |
| Controls | A bar pinned to the bottom edge that does not fade, collapsible to one button; arrow keys move the level by 5 points |
| Display sleep | Wake lock requested for the whole session, because a fill light that dims halfway through a call is worse than none |
Frequently asked questions
Can a monitor genuinely work as a video-call light?
Yes, and the number is better than people expect: a 27-inch 16:9 panel is 0.201 m² of emitting surface, so at 400 cd/m² it puts out around 250 lumens, and a 24-inch at 300 cd/m² still manages about 150. What makes it flattering is not the quantity but the size — the softness of a light comes from how large it looks from where you are sitting, and a screen 60 cm away subtends roughly twice the angle a 25 cm ring light does at the same distance, so the shadow edges under your chin are correspondingly gentler. The catch is that it lights you flat and from directly in front, and it leaves a rectangular catchlight in your eyes that a viewer will recognize.
Which color temperature should I pick?
Match whatever is already lighting the room rather than picking the one that looks nicest on its own. A webcam sets one white balance for the whole frame, so if a 2700 K bulb is behind you and a 6500 K screen is in front, the camera splits the difference and one of the two ends up strongly colored — usually your face. The warm preset looks orange when you stare at it directly and looks like nothing at all once the camera has adapted to it, which is the point.
Is 50% on the slider the same as half brightness?
No, and this is the number most white-screen pages get wrong. sRGB stores light on a curve of roughly 2.2, so halving the code value does not halve the light: 50% of the code range emits about 22% of full output, and 60% emits about 33%. The readout prints both figures for that reason. Nothing here touches your monitor's backlight either — every control on this page works inside the image, above the panel's own brightness setting, so the dimmest this page can go is a dark image on a screen still lit to whatever level you left it at.
One side of the white looks warmer than the other. What is that?
Rule out software before you blame the panel, in this order: a blue-light filter such as Night Light, Night Shift or f.lux, which warms the whole screen on a schedule and is the answer more often than anything else; then a display profile or a vendor picture mode left on Warm; then the panel itself. A genuine hardware tint gradient across the width of the screen is a color-uniformity fault, and it is judged against ramps and gray steps on the monitor color test rather than against a single white field.
Will hours of full white damage the screen?
On an LCD it costs nothing beyond running the backlight, which ages slowly and evenly whatever the image is. On an OLED it does age the emitters, but a full-field white ages all of them at the same rate, which is far less harmful than a static bright element sitting in one place — an evenly worn panel just gets dimmer, while an unevenly worn one shows a permanent ghost. Extended use as a lamp is still worth doing at a lower level rather than at maximum, on any panel type.
Why can this page not make my screen brighter?
Because no browser exposes the backlight. A web page can only change the pixels, and the pixels are already at their maximum when the field reads #FFFFFF — everything above that is the monitor's own brightness control, the operating system's slider on a laptop, or the ambient-light sensor deciding for you. If the field looks dim, turn the panel up; there is no software route to it from here.
Does it work as a light box for tracing?
For thin paper and short sessions it does, and daylight at full output is the right setting. Two warnings that apply to a screen and not to a real light box: a monitor is not built to be pressed on, and pushing a pencil against an LCD leaves temporary pressure marks in the crystal that can take hours to clear, while a laptop screen leans back under any pressure at all. Tape rather than lean, and lay the sheet flat on the glass without weight on it.
About using a panel as a light source
A display showing white behaves like a large, diffuse, almost perfectly even emitter, which is exactly the shape of light portrait photographers spend money on. The output follows from the specification sheet: luminance in cd/m², multiplied by the emitting area, multiplied by π for a surface that radiates into a hemisphere. A 24-inch 16:9 panel is 0.159 m² and a 27-inch is 0.201 m², so a mid-range monitor between 300 and 400 cd/m² lands somewhere between 150 and 250 lumens — modest against a room light, and plenty at arm’s length. Softness is the more useful property: how hard a shadow edge looks is governed by the apparent size of the source, and a whole monitor at 60 cm is enormous compared with a small LED panel at the same distance, which is why the result flatters even though the quantity of light is unremarkable. If you do not know the physical dimensions of your own screen, the monitor size comparison gives width and height in centimeters for any diagonal and aspect ratio.
Color temperature is where a screen used as a light goes wrong, and the reason is that a webcam picks one white balance for the entire frame. sRGB pins its white point at D65, about 6504 K, so a panel at full output is already daylight; put that in front of someone sitting under a 2700 K bulb and the camera has to choose, and it usually chooses wrong in the direction of your skin. The four presets here are emission colors, taken from the usual blackbody approximation and rounded to 8-bit values, not calibration targets — the warm one looks distinctly orange if you stare at it and disappears entirely once the camera has adapted. Judging whether the panel itself renders color correctly is a different exercise with gray ramps and a gamma target, and it lives on the monitor color test. While the light is on your face, the webcam mirror is the quickest way to see what the camera makes of it.
The second job for a white field is inspection, and it is worth knowing what it can and cannot show. Surface dust, fingerprints and the greasy film that builds up over a keyboard all stand out immediately, especially viewed at a shallow angle where they catch reflections. Specks that do not move when you wipe are inside the stack — typically dust that settled on the diffuser during assembly — and no cleaning reaches them. A white that looks creamy against a sheet of printer paper is usually a blue-light filter or a Warm picture mode rather than an aged panel, so turn those off before concluding anything. A single dark dot that stays put across every image is a pixel fault rather than dirt, which the dead pixel checker confirms in five fields, and patchy brightness across the sheet is a uniformity problem better judged from the dark end on the backlight bleed test. One more thing a static white field is good for: it is the least demanding image a GPU can draw, so if the screen still stutters while showing it, the fault is in the frame pipeline rather than in the content, and the fps test counts what your browser is actually delivering.
Where the settings live
Every number on this page is worked out by JavaScript running in the tab you are reading it in. Nothing you type, paste or open is uploaded, logged or kept, which is also why the tools carry on working after you disconnect from the network.
Your chosen temperature and level exist as two numbers in this tab and nowhere else — not in a cookie, not in local storage, not on a server — so reloading the page brings back daylight at full output. The camera is never opened by this page, because filling a screen with light needs nothing from it.