A wider wick gives a bigger flame and burns more fuel: about 3 to 5 mm for a nightlight, 8 to 12 mm for reading, and 15 to 20 mm for work in a workshop or kitchen. Choose the narrowest wick that gives enough light, because a single moderate lamp also gives off a couple of hundred watts of heat and burns fuel in proportion.
Part of Oil Lamp Construction
A wick’s width sets the size of the flame, the rate fuel is burned and the heat released. Nearly all of a lamp’s fuel energy leaves as heat rather than light.
Width Is The Main Control Over Brightness
| Wick width | Brightness | Fuel use | Use case |
|---|---|---|---|
| 3-5 mm | Dim (nightlight) | Very low | Sleeping area, navigation |
| 8-12 mm | Moderate (reading) | Moderate | General living area |
| 15-20 mm | Bright (work light) | High | Workshop, kitchen, surgery |
| Multiple wicks | Very bright | Very high | Large room, signalling |
The overview’s fuel figures (about 20 ml/h for kerosene, 25 ml/h for tallow, 28 ml/h for lard, 30 ml/h for vegetable oil) are for a moderate wick. A narrower wick burns less; a wider one burns more.
Every Flame Is Also A Heater
A lamp turns almost all of its fuel into heat, not light. Using standard energy values (kerosene about 35 MJ per litre; animal fat about 37.7 kJ per gram, which is the usual 9 kcal/g; fat density about 0.9 g/ml):
- Kerosene at 20 ml/h: 0.020 L × 35 MJ/L = 0.70 MJ per hour; 0.70 MJ ÷ 3,600 s ≈ 194 W.
- Tallow at 25 ml/h: 25 ml × 0.9 g/ml = 22.5 g; 22.5 g × 37.7 kJ/g ≈ 848 kJ per hour; ÷ 3,600 s ≈ 236 W.
- Lard at 28 ml/h: 28 × 0.9 = 25.2 g; × 37.7 kJ/g ≈ 950 kJ per hour; ≈ 264 W.
A person at rest gives off roughly 100 W. One moderate lamp therefore heats a room about as much as two or three people sitting in it. That helps in winter; it also means a lamp adds to heat in a small room, consumes air, and — if the wick is too high — makes carbon monoxide.
Method: Setting The Flame
Step 1: Fit the wick to the holder. It should slide but not rattle.
Step 2: Light and wait. Let the flame settle for a minute.
Step 3: Raise gradually. Raise the wick until the flame gives the light you need, then stop.
Step 4: Watch the tip. A steady flame with a clean tip is right. If the flame is tall, ragged, or has a dark trail of smoke, it is too high; lower it.
Common Mistakes
- Choosing the widest wick “for safety”. A wider wick burns more fuel and makes more heat and soot.
- Raising the wick to chase brightness. Past a point more wick gives only smoke. Add a reflector or a second small wick instead.
- Ignoring fuel viscosity. Molten fat may need a wider or looser wick than kerosene to deliver the same flow.
Safety
A tall flame is an incomplete one
A flame turned up until it smokes burns incompletely, and incomplete burning makes carbon monoxide, which has no colour or smell. The early symptoms (headache, nausea, drowsiness) feel like normal tiredness. If you feel sleepy near a lit lamp, put the flame down, ventilate with an inlet and an outlet, and get into fresh air; do not lie down to rest.
What’s Next
- Learn next: Improving Brightness — cheaper ways to get more light than a bigger flame
- Combine with: Wick Trimming — keeping the tip clean at any size