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Room Lighting Calculator
Calculates the total lumens a room needs for its purpose, and how many bulbs of a given output that means.
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Enter your figures and press Calculate.
In short
Room Lighting Calculator is a free online tool on inputtesthub.com that calculates the total lumens a room needs for its purpose, and how many bulbs of a given output that means. It needs no account, no download and no payment, and there is no daily usage limit. Everything is processed inside your own browser, so the data you paste is never uploaded to a server.
How to use the Room Lighting Calculator
- Enter your figures in the input fields.
- The result updates as you type, together with the full working.
- Check the breakdown table to see exactly how the number was reached.
About the Room Lighting Calculator
The Room Lighting Calculator calculates the total lumens a room needs for its purpose, and how many bulbs of a given output that means. It runs as plain JavaScript inside the page, which means there is no upload step, no queue and no size limit imposed by a server — the only limit is your own device.
What people use it for
- Buying the right brightness of bulbs.
- Planning downlights for a new room.
- Working out why a room feels dim.
Details
| Living room | 150 lux |
|---|---|
| Kitchen worktop | 500 lux |
| Home office | 500 lux |
| LED efficiency | ≈ 90 lm/W |
| 800 lm | ≈ an old 60 W bulb |
The maths behind it
This tool uses Total lumens = floor area in m² × the target lux for that room type. Number of fittings = total lumens ÷ lumens per bulb. Every intermediate value is shown on screen, so the result can be checked by hand.
Buy bulbs by lumens, not watts — an LED producing the light of a 60 W bulb draws about 9 W. One ceiling fitting rarely gives an even level either: several smaller sources beat one bright one.
Frequently asked questions
How many lumens do I need for a living room?
About 150 lux across the floor area, so a 14 m² living room needs roughly 2,100 lumens — around three 800-lumen bulbs. Task areas such as a reading chair want their own lamp on top of that.
Are watts or lumens the right measure of brightness?
Lumens. Watts measure electricity consumed, and an LED delivers the same light as an old 60 W bulb on about 9 W — comparing wattages across technologies tells you nothing useful.
Are there any usage caps on the Room Lighting Calculator?
No charge and no sign-up. There is no free tier to run out of because there is no paid tier — inputtesthub.com is funded by advertising rather than by metering the tool.
Is what I paste into the Room Lighting Calculator stored?
No. The Room Lighting Calculator runs entirely in your browser using JavaScript. Nothing is transmitted, logged or stored, which you can verify yourself in the Network tab of your browser's developer tools.
Can I check the maths myself?
It uses Total lumens = floor area in m² × the target lux for that room type. Number of fittings = total lumens ÷ lumens per bulb. The full working is printed under the result, so you can follow every step rather than trusting a black box.
What do people use the Room Lighting Calculator for most?
In practice it gets used for three things: buying the right brightness of bulbs. Planning downlights for a new room. Working out why a room feels dim. It is built for exactly those cases rather than being a general-purpose tool with this bolted on.
What do people usually get wrong here?
Buy bulbs by lumens, not watts — an LED producing the light of a 60 W bulb draws about 9 W. One ceiling fitting rarely gives an even level either: several smaller sources beat one bright one.
What are the key numbers for the Room Lighting Calculator?
Living room is 150 lux. Kitchen worktop is 500 lux. Home office is 500 lux. These are printed on the page itself, so you do not have to take them on trust.
Is the number rounded?
The calculation runs in double precision and the result is shown to ten significant figures, so converting a value and converting it back returns the original. What is displayed is rounded for readability; what is copied is not.
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