Daylight / 02
Lights-On Reminder
Find out when your room gets too dark to work at a screen, especially on grey days, and get a reminder to turn the lights on, from the weather forecast, your camera, or a threshold you teach it.
Lights-On Reminder: TOEA turns the forecast's solar radiation into a rough estimate of the light at your desk, shows today's curve and when it falls below the working target, and warns you when it does. The optional camera check watches the room's brightness trend, and the button stores your own threshold. Runs 100% locally in your browser with zero server file uploads.
- Category
- Everyday tools
- Runs
- In your browser
- Cost
- Free · no sign-up
- Availability
- Ready to use
Runs in your browser. The weather forecast, if you turn it on, is the only request it makes.
Place: London, United Kingdom · 51.51° N, 0.13° W · Europe/London
The room figure is the rough share of outdoor daylight that reaches your desk. It varies a lot with window size, distance, and what is outside, which is why the learned threshold below works better.
When on, the page asks api.open-meteo.com for today's solar radiation at your coordinates rounded to 0.1° (about 11 km), and again every 15 minutes while it is open. That request is the only thing that leaves your browser. When off or offline, the estimate comes from the sun's position, assuming an overcast sky.
Your threshold
Press this the next time you reach for the switch. The page remembers the light at that moment, in this browser only, and warns you at that level from then on.
Camera check (optional)
Measures the room itself: a tiny 32 × 24 copy of one frame every 90 seconds is averaged into a brightness figure. Frames are never stored or sent, and the camera is released when you stop. Cameras adjust their exposure automatically, so the figure shows a trend, not lux.
Alerts
Reminders only work while this tab is open. It can sit in the background, where browsers may slow its checks to about once a minute; closing the tab or letting the computer sleep stops them.
Dim light does not damage your eyes: the American Academy of Ophthalmology says reading or working in low light can cause eye strain and fatigue, not lasting harm. Turning the lights on, and setting the screen about as bright as the room around it, makes long sessions more comfortable.
From a weather forecast to light at your desk
Forecasts give solar radiation on a flat surface in watts per square metre. Daylight gives roughly 100 to 125 lumens per watt, so the page multiplies by 115 to get outdoor lux: an overcast day ranges from about 1,000 lux under heavy cloud to 20,000 or more under bright cloud, and direct summer sun exceeds 100,000. Indoors, a desk gets only a small share of that, the daylight factor: around 5% beside a large window, 2% in an average room, 1% or less a few metres back.
Every step is approximate, so the lux figure can easily be out by a factor of two. The timing is steadier: the curve falls in the same way whatever the room, which is why one press of the calibration button improves every later reminder.
How much light is enough
EN 12464-1, the European standard for workplace lighting, lists 500 lx of maintained illuminance for writing, typing, reading, and data processing. Home desks are often darker, and many lighting guides treat about 300 lx as the lowest comfortable level for desk work. Below that, the contrast between a bright screen and a dim room makes eyes work harder.
Dim light does not damage the eyes; the American Academy of Ophthalmology describes the effect as strain and fatigue. When you turn the lights on, lower the screen's brightness until a white page no longer glows against the wall behind it. The monitor test is useful for checking the display itself.
What the camera can and cannot tell
Webcams adjust exposure automatically to keep the picture evenly bright, so average frame brightness changes far less than the room does. Where the browser reports exposure time and ISO, which depends on the camera and the browser, the page divides them out and the trend is closer to the real change; otherwise the percentage understates it.
Point the camera at the room rather than a window or your face, and take a new baseline if you move it. Check what yours reports with the webcam test, and see when the sun actually sets with sunrise and sunset times.
How to use it
- Pick your place and how much daylight your room gets.
- Turn on the forecast, the camera check, or both, and allow notifications.
- Press I just turned the lights on the next time you do, so later reminders match your room.
Privacy & limitations
Everything runs in your browser. With the forecast on, the only request is to Open-Meteo with your coordinates rounded to 0.1°. Camera frames are reduced to one brightness number and never stored or sent. Your threshold is kept in this browser only.
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Frequently asked questions
How accurate is the lux estimate?
Rough: expect it to be off by a factor of two either way, because the light reaching a desk depends on window size, distance, and what is outside. The time it predicts is more useful than the number, and pressing I just turned the lights on makes it match your room.
Why 300 or 500 lux?
The European standard for workplace lighting, EN 12464-1, lists 500 lux for writing, typing, reading, and data processing in offices. 300 lux is offered as a practical minimum for a home desk; many people find less than that tiring for long.
Will it remind me with the tab closed?
No. It works only while the page is open; it can be in a background tab, where the browser checks about once a minute. Closing the tab or letting the computer sleep stops the reminders.
Does working in dim light damage my eyes?
No. According to the American Academy of Ophthalmology, dim light causes eye strain and fatigue but not lasting damage. Turning the lights on and matching the screen's brightness to the room makes long sessions more comfortable.
Free tool · runs in your browser · no account required