CandleClear

How does a candle work?
A candle is a lamp that carries its own solid fuel, builds its own cup and trims its own wick. Cut one open in 3D, break its feedback loop, and repeat the experiments Faraday did for children in 1848.

▶ Play with it  ·  Read the 60-second explainer  ·  Watch the 40-second video

In 60 seconds

1. A lamp that builds its own cup. A candle is an oil lamp that carries its fuel as a solid. The flame melts a small pool of wax, the cool outer edge stays solid and holds the pool like a cup, and a cotton wick lifts the liquid to the flame. A flat braided wick curls into the hot edge of the flame and burns its own tip away, so nobody has to trim it.
2. A machine that runs itself. The flame sets the size of its own fuel pool, and the bare wick standing above the pool sets the size of the flame. This feedback loop settles at about 6 grams of wax an hour. Only about 3 of the flame's 80 watts go back to melt and boil the fuel. A wick too thick drips and smokes, a wick too thin tunnels, and a draught makes the candle gutter.
3. What Faraday showed. Solid wax does not burn and nor does liquid wax. The flame burns wax vapour. Faraday led that vapour out of the dark middle of a flame through a glass tube and lit it, and relit a blown-out candle through its white trail. Burning 1 gram of paraffin takes 3.45 grams of oxygen and makes 3.12 grams of carbon dioxide and 1.33 grams of water.
4. Mostly heat, a little light. A candle releases about 80 watts but only about 13 lumens: roughly 0.15 watts of visible light, from glowing soot. That is about one candela, because the unit of light began in 1860 as a real candle made of whale wax. It was redefined with glowing platinum in 1948 and with green light in 1979, each time tuned to match the candle.
5. Waxes, hot days and scent. Paraffin melts between 46 and 68 °C, beeswax at 62 to 64 °C, and all waxes soften well below that, which is why candles bend in an Indian summer. In a hot room the same flame melts a wider pool and a thin candle drips. A scented candle smells strongest once its pool is warm, because warmth pushes the fragrance into the air.
6. Smoke, safety and meaning. In chamber studies a steady flame gave off about 0.3 to 2.4 milligrams of fine particles an hour. A flame flickering in a draught gave roughly ten times more, mostly soot. Fire services ask for 30 cm between a candle and anything that burns, and never to leave it alone. Candles still mark power cuts, prayers, birthdays and vigils.

Words worth knowing

Term	Meaning
Melt pool	The small pond of liquid wax round the wick. Only liquid wax can climb the wick and burn.
Self-trimming wick	A flat braided wick that curls into the edge of the flame, where its tip burns away. Introduced in France in 1825.
Feedback loop	A chain of causes that circles back on itself. In a candle, flame size sets pool size and wick length sets flame size.
Wax vapour	Wax turned to gas by the flame's heat. It fills the dark middle of the flame and is the fuel that actually burns.
Soot	Tiny grains of carbon made inside the flame. Hot, they glow yellow and give the light. Escaped, they are black smoke.
Candela	The SI unit of how strongly a lamp shines in one direction. A candle is about one candela, which is 12.6 lumens all round.
Paraffin wax	A white wax from petroleum, made of chains of 20 to 40 carbon atoms, melting between about 46 and 68 °C.
Tunnelling	A flame too small for a wide candle melts only the middle and sinks down a hole, leaving a wall of wax.
PM2.5	Particles in the air smaller than 2.5 thousandths of a millimetre. A flickering candle gives off about ten times more than a steady one.

A short history

About 2,700 years, from Etruscan candlesticks to a blue flame in orbit and a unit of light that still carries the candle's name.

• 1462 · Two trades, two guilds (The Tallow Chandlers and the Wax Chandlers, London, England)
• 1823 · Chevreul takes fat apart (Michel Eugène Chevreul and Joseph Gay-Lussac, Paris, France)
• 1825 · The wick that trims itself (Cambacérès, France)
• 1850 · Paraffin: wax from coal and oil (Carl Reichenbach and James Young, Germany, and Bathgate, Scotland)
• 1860 · Faraday and the candle (Michael Faraday, edited by William Crookes, Royal Institution, London, England)
• 1860 · One candle becomes a unit of light (Parliament of the United Kingdom, London, England)
• 1948 · The candle becomes the candela (General Conference on Weights and Measures, Paris, France)
• 1992 · A candle burns in orbit (Daniel Dietrich, Howard Ross, James T'ien and astronaut Shannon Lucid, Space Shuttle Columbia and the Mir space station)

The full story, with 30 moments, charts, people and 61 sources: glassbox.how/e/candleclear/history. The data lives in history.json.

Video and slides

Made with the Glassbox studio from this box's storyboard (window.glassbox.director). Free to reuse under CC BY 4.0.

File	What	Size
glassbox/reel.mp4	Reel / Short, with captions and soundtrack	1080×1920
glassbox/video.mp4	YouTube video, with captions and soundtrack	1920×1080
glassbox/slide-1…10.jpg	Instagram carousel	1080×1350
glassbox/thumb.jpg	YouTube thumbnail	1280×720
glassbox/cover.jpg	Share card and repo social preview	1200×630
glassbox/history-reel.mp4	“History in 10 moments” Reel / Short	1080×1920
glassbox/history-slide-*.jpg	History carousel	1080×1350
glassbox/post.json	Post copy and schedule used by the publish kit

Privacy

This box has no accounts and no ads, and it ships its own fonts and libraries. When you run it yourself it sends nothing anywhere. On glassbox.how, the site's /bar.js also loads Glassbox's analytics: Google Analytics to count visits (it asks first in the EU, UK and Switzerland, and stays off when your browser sends Global Privacy Control or Do Not Track) and ClickTrust to detect bots.

It remembers a few things in your own browser only, and never sends them anywhere:

Browser storage key	What it holds
candleclear.v1	Which chapters you have opened, your best quiz scores, and sound on or off.

Exactly what each one sees is at glassbox.how/privacy.

Licences

• Code: MIT. Use it, change it, ship it.
• Explanations, text, images and videos (glassbox.json, glassbox/): CC BY 4.0. Credit “Glassbox, glassbox.how/e/candleclear”.
• Third-party parts keep their own licences: three.js (MIT), Geist, Instrument Serif (SIL OFL 1.1).
• The Glassbox name and logo aren't covered by either licence. See the terms.

Found a mistake? Open an issue. Corrections happen in public.

Run it

It's plain HTML, CSS and JavaScript. No build step and no dependencies. Run locally, it contacts no other website.

python3 -m http.server 8000

Three.js and the fonts ship in vendor/ and fonts/, so it also works offline.

Then open http://localhost:8000.

How it's built

File	What
index.html, css/app.css	The page and its styles
js/app.js, js/stage.js, js/ui.js, js/kit.js	The shared Glassbox 3D engine: chapters, 3D stage, controls, quiz, video director
js/chapters/*.js	One file per chapter: the 3D model, controls, text, key terms, quiz and video scenes
js/candle.js	Shared parts for the chapters: wax properties, the candle's feedback model, the room-smoke sum, the 3D candle and flame, chart boards
glassbox.json	Title, question, explainer beats, key terms, browser storage and credits shown on glassbox.how
reel in each chapter	The storyboard the Glassbox studio records into short videos
glassbox/	The published video, slides, thumbnail and post copy
fonts/, vendor/three/	Self-hosted Geist and Instrument Serif (SIL OFL 1.1) and three.js (MIT)