70 m² study or desk — 35000 lumens
A room at 500 lux needs 35000 lumens. That is 350 watts of LED, or 44 bulbs of 800 lumens.
Watts are not brightness
Equal lumens mean equal brightness; what changes is the electricity. An LED makes 100 lumens per watt, a filament 13 — nearly eight times apart. The monthly figure below assumes five hours a day for thirty days.
- LED100 lm/W350 W
- fluorescent60 lm/W583.3 W
- halogen20 lm/W1750 W
- incandescent13 lm/W2692.3 W
- Light reaching the floor
- 500 lux
- Light you need
- 35000 lm
- Room size
- 70 ㎡
- In pyeong
- 21.2
- In 800-lumen bulbs
- 44
- A month of electricity
- 52.5 kWh
- Extra watts if incandescent
- 2342 W
Several lamps beat one
The same lumens crammed into one fitting light the spot beneath and leave the corners dark. Splitting them across several 800-lumen lamps softens shadows, and one failure no longer means a dark room.
Nearby cells
Same room, other uses
Same use, other sizes
How to read this
- The light you need is lux times floor area; the use decides the lux.
- Watts are only that light divided by the lamp’s efficacy — not a measure of brightness.
- Bulb counts round up from one 800-lumen lamp.
- Ceiling height, wall colour and shades are not in this calculation.
Frequently asked questions
Q. How many lumens for a 70 m² study or desk?
35000 lumens — 500 lux times the floor area.
Q. How many watts should the lamp be?
350 W as LED, 583.3 W as fluorescent. An incandescent would draw 2692.3 W — 2342 W more.
Q. How many bulbs do I need?
44 at 800 lumens each. Spread them out rather than stacking them in one fitting.
Q. What does it cost to run?
On LED at five hours a day, 52.5 kWh a month.