cd
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Convert between candela, lumens, lux, footcandles, millicandela, and watts
lm = cd × 4π (isotropic source)lx = cd / d² (d in meters)
Founder & CEO, Toolraxy
Faiq Ur Rahman is a web designer, digital product developer, and founder of Toolraxy, a growing platform of web-based calculators and utility tools. He specializes in building structured, user-friendly tools focused on health, finance, productivity, and everyday problem-solving.
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A lighting calculator is a specialized tool that converts between different units of light measurement and helps you understand how illumination changes with distance. Lighting is measured in several ways – total light output (lumens), light intensity in a specific direction (candela), and how much light actually reaches a surface (lux or footcandles).
This calculator handles all these conversions simultaneously. Change one value, and all other units update instantly. It also accounts for distance (because light diminishes as you move away from the source) and light source efficiency (how many lumens per watt a bulb produces).
The problem: Lighting is confusing. Bulb packages advertise lumens, but building codes specify lux requirements. Electricians talk in footcandles, but energy guides show watts. Photographers need candela, while interior designers think in lumens per square foot. Without a conversion tool, you’re guessing – and guessing wrong can mean rooms that are too dark, energy bills that are too high, or workspaces that don’t meet safety standards.
The cost of confusion:
Over-lighting wastes energy (up to 30% higher electricity bills)
Under-lighting strains eyes and reduces productivity
Wrong bulb choices mean buying twice
Non-compliant lighting can trigger OSHA fines
What this calculator reveals:
True light output – Convert lumens to lux based on your room size
Efficiency comparisons – See actual wattage needed for target brightness
Distance impact – Understand how far light travels before fading
Unit conversions – Speak any lighting language fluently
Enter any lighting value – Type into candela, millicandela, lumens, lux, footcandles, or watts
Adjust distance – Set how far the light is from the surface you’re measuring
Choose distance unit – Meters or feet (calculator handles conversion automatically)
Set light source efficacy – Use presets (LED, incandescent) or enter custom lm/W
Watch all values update – See every measurement change in real time
Pro tip: Start with the unit you know best. If you have a bulb rated in lumens, enter that. If you need to meet a lux requirement for a workspace, enter the lux value and see what bulb you need.
Light measurement involves several related concepts:
Luminous Intensity (Candela) – How bright a light appears in a specific direction. Think of a spotlight: it has high candela because it concentrates light.
Luminous Flux (Lumens) – The total visible light emitted by a source in all directions. A 60W incandescent bulb produces about 800 lumens.
Illuminance (Lux & Footcandles) – How much light actually reaches a surface. One lux = one lumen per square meter. One footcandle = one lumen per square foot.
The Inverse Square Law: Light intensity decreases with the square of the distance. Double the distance, and you get only one-quarter the light. This is why distance matters so much in lighting design.
Efficacy (Lumens per Watt) – How efficiently a light source converts electricity into light. LEDs (100 lm/W) are far more efficient than incandescents (15 lm/W).
Scenario: You’re designing task lighting for a home office desk. The recommended illumination for detailed work is 500 lux.
| Step | Action | Result | |
|---|---|---|---|
| 1 | Enter 500 in the lux field | Calculator shows all equivalent values | |
| 2 | Set distance to 2 meters (desk height from ceiling) | Values adjust automatically | |
| 3 | Check lumens required | Approximately 6,283 lumens needed | |
| 4 | Compare light sources | LED: ~63W | Incandescent: ~419W |
The verdict: With LEDs, you need about 63W of lighting (e.g., 4-6 LED bulbs). With incandescents, you’d need over 400W – impractical and expensive. This calculator just saved you from installing inadequate lighting or overspending on energy.
✓ Six units in one – Candela, millicandela, lumens, lux, footcandles, watts
✓ Real-time updates – Change any value, see all others instantly
✓ Distance matters – Accounts for how far light travels
✓ Dual distance units – Meters or feet, with automatic conversion
✓ Source presets – LED, incandescent, halogen, CFL with typical efficacy values
✓ Custom efficacy – Enter any lm/W value for specialty bulbs
✓ No installation – Works in any browser, on any device
✓ Educational – Learn lighting relationships by experimenting
| User Type | How They Benefit |
|---|---|
| Homeowners | Choose right bulbs for each room |
| Interior designers | Calculate lighting levels for design specs |
| Electricians | Verify installations meet code requirements |
| Photographers | Set up studio lighting precisely |
| Facility managers | Ensure commercial spaces are properly lit |
| Energy auditors | Calculate savings from lighting retrofits |
| Students | Understand photometry principles |
| DIY renovators | Plan kitchen, bathroom, and task lighting |
Lumens measure total light output; lux measures light on a surface. A 1000-lumen bulb provides 1000 lux if all light hits one square meter, but only 100 lux if spread over 10 square meters.
Light drops off dramatically with distance. A light that seems bright at 1 meter may be inadequate at 3 meters. Always enter the actual distance from light to surface.
Feet and meters are not interchangeable in lighting calculations. Use the distance unit selector to ensure accuracy.
LEDs vary from 70 to 150 lm/W. Incandescents are consistently 12-18 lm/W. Use the presets for estimates, but verify actual bulb specifications.
This calculator assumes light spreads equally in all directions. Spotlights, track lighting, and directional fixtures will have different actual lux values.
Omnidirectional assumption – Best for bare bulbs, not directional or reflector lights
Point source assumption – Large fixtures may not follow inverse square law at close distances
No beam angle adjustment – Doesn’t account for focused or spread light patterns
No color temperature – Doesn’t distinguish between warm and cool light
Typical efficacy values – Actual bulb efficiency varies by manufacturer
No room surface effects – Doesn’t account for wall colors, reflections, or absorptions
Clear air assumed – No correction for fog, smoke, or atmospheric conditions
Gone are the days when we bought bulbs by watts. Lumens are now the standard measure of brightness. A 60W incandescent produces about 800 lumens. An LED producing the same 800 lumens uses only 8-10 watts. When shopping for bulbs, look for lumens first, then check efficacy (lm/W) to find the most efficient option. This calculator helps you translate between old and new measurements instantly.
Different activities need different light levels. General living: 100-200 lux. Kitchen tasks: 300-400 lux. Reading and office work: 400-500 lux. Detailed craft work: 750-1000 lux. Commercial spaces often have specific requirements – offices typically need 500 lux at desk height, while hallways can function at 100 lux. Use this calculator to determine if your planned lighting meets these targets.
Light spreads out as it travels. Imagine a balloon expanding – the same amount of light covers a larger area the farther you go. At twice the distance, the light covers four times the area, so each square gets only one-quarter the light. This is why ceiling height dramatically affects how much light reaches your desk. A light at 10 feet provides only one-quarter the illumination of the same light at 5 feet.
Incandescent bulbs convert only 5-10% of energy into light – the rest becomes heat. LEDs reverse this, converting 80-90% into light. This calculator shows the real-world impact: a 10W LED can replace a 60W incandescent while producing the same light. Over 25,000 hours (typical LED life), that’s 1,250 kWh saved – about $150 at average electricity rates.
Good lighting uses layers: ambient (general illumination), task (focused on work areas), and accent (highlighting features). Ambient lighting typically needs 10-20 lumens per square foot. Task areas need 30-50 lumens per square foot. Use this calculator to convert these recommendations into actual bulb requirements for your specific room dimensions.
While this calculator handles brightness, color matters too. Color temperature (measured in Kelvin) ranges from warm (2700K, like incandescents) to cool (5000K, like daylight). CRI (Color Rendering Index) measures how accurately colors appear under the light. For homes, aim for 2700K-3000K and CRI 90+. For task areas, 3500K-4000K improves visibility. These factors work alongside brightness to create effective lighting.
Lumens measure total light output from a source. Lux measures how much light actually reaches a surface. One lux equals one lumen per square meter. Think of lumens as “how much light is produced” and lux as “how much light arrives here.”
Divide lumens by the area in square meters to get lux. For example, 1000 lumens spread over 10 square meters = 100 lux. Our calculator does this automatically when you enter distance.
A footcandle is the imperial unit of illuminance. One footcandle equals one lumen per square foot. It’s commonly used in US building codes and lighting standards. 1 footcandle = approximately 10.764 lux.
General living spaces need 10-20 lumens per square foot (roughly 100-200 lux). Task areas like kitchens and offices need 30-40 lumens per square foot (300-400 lux). Detailed work may require 50+ lumens per square foot (500+ lux).
Quality LED bulbs typically achieve 80-100 lumens per watt. Premium LEDs can reach 130-150 lm/W. Compare this to incandescent (15 lm/W), halogen (20 lm/W), and CFL (60 lm/W).
Light follows the inverse square law: double the distance, and you get one-quarter the light. At 2 meters, you get 25% of the light you’d have at 1 meter. At 3 meters, you get only 11%.
For an omnidirectional light source, 1 candela equals approximately 12.57 lumens (4π lumens). This relationship comes from the definition of candela as lumens per steradian (a unit of solid angle).
Yes, but remember that outdoor lighting must account for much larger distances. Enter the actual distance from the light to the ground or surface you’re illuminating.
Wattage = lumens ÷ efficacy. If you know your bulb’s actual efficacy (check the package), the calculation is accurate. Using presets gives estimates within typical ranges.
It means the calculator assumes light spreads equally in all directions from a single point. Most household bulbs approximate this, but directional lights (like recessed cans) do not.
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