How to use the classroom light
- Open this page on the computer that drives your projector or board and press Start measuring. Allow the microphone when the browser asks.
- Pick the setting for the lesson: Quiet work, Silent reading or Group work. Each one sets the level at which the light turns amber and red.
- Press Full-screen light. The class sees a large traffic light, the current level and the thresholds. Press Esc or Exit full screen to go back.
- Tick the alarm if you want a short chime after 2 seconds of red. It never sounds more than once every 10 seconds.
Picking thresholds that work in your room
Two measurements explain the range. With nobody in it, a classroom should be quiet: WHO’s Guidelines for Community Noise (1999) ask for background noise below 35 dB LAeq during lessons, and the American standard for classroom acoustics, ANSI/ASA S12.60, sets a background noise limit of 35 dB(A) for core learning spaces. With a class at work, levels are much higher. When Bridget Shield and Julie Dockrell surveyed 16 London primary schools, 110 occupied classrooms averaged 72.1 dB LAeq, with a background (LA90) of 54.1 dB between the louder moments (ICBEN 2008); their earlier report found a difference of 20 dB LAeq between the quietest and the noisiest activities (Journal of the Acoustical Society of America, 2004).
The three settings sit inside that range, from silent reading well below the average of a working class to group work just above it. Treat them as a starting point. A laptop or board microphone reads the room differently from a sound level meter, the class’s distance from it matters, and so does the room itself. Watch the light through one lesson and move the numbers until red means what you want it to mean. If you have a sound level meter or a calibrated app, calibrate once and the numbers become comparable from room to room.
Why the light doesn’t flicker
The light follows the Slow time weighting, a one-second average from the sound level meter standard IEC 61672-1, rather than the instant level. It changes up as soon as the average crosses a threshold and changes back only when the level has dropped 1 dB below it. A single clap or a chair scraping hardly moves a one-second average; a room that gets louder for a second or two does, which is the behavior worth showing.
The meter measures levels only: nothing the class says is recorded or leaves the computer.
How this page is set up
This is the same meter as the standard decibel meter, opened with different settings. You can change any of them while it runs, and your calibration works on every page.
| Setting | This page | Standard meter |
|---|---|---|
| Opens on | Classroom light | Calibrate |
| Weighting | A, Slow | A, Fast |
| Classroom thresholds | Quiet work: amber 55, red 65 dB; Silent reading: amber 45, red 55 dB; Group work: amber 65, red 75 dB | Amber 60, red 70 dB |