Lighting Level Calculator
Number of luminaires needed for a target illuminance. With the formula, a worked example and typical values.
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Estimate only. Not engineering or safety advice. Check the result against the applicable standard and the equipment data, and have a competent engineer review it before it is relied on. Terms of use.
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About this calculator
This page calculates luminaires and luminaires from required illuminance, room area, lumens per luminaire, utilisation factor and 1 more input. Change any value or its unit and the result updates. The steps below show the working for the default values, so you can check each line against your own method.
Limits of this calculator
Check uniformity and glare separately; the count is a starting point for layout.
Cross-check: 6 reference cases, calculated from textbook formulas coded separately from the engine by the same author, agree with this calculator. This is not an independent review.
Verification status: Indicative
Indicative. Estimation only; further engineering checks are required. Basis: Lumen-method estimate.
What this calculator checks
- The arithmetic of the simplified model for the values you entered.
What remains unverified
- Whether the simplifying assumptions listed on this page hold for your case.
- Any standard, manufacturer or site data. Treat the result as an estimate and confirm it by a further engineering check.
Verification register entry
| Calculation author | Rahul Sharma (author) |
|---|---|
| Technical review | No independent technical review has been carried out |
| Individual professional approval | Not recorded |
| Formula reference | not recorded |
| Standard and edition | ISO/CIE 8995-1, 2025 Ed 1 |
| Standard review state | Public-scope screened; licensed clause review still pending |
| Scope-screening note | Indoor workplace lighting requirements and maintained-illuminance criteria are relevant. The lumen-method equation is a simplified planning method; use luminaire photometry, room data and project-specific criteria for design. |
| Cross-check test cases | 6 reference vectors (tests/reference_vectors.json) |
| Review date | not recorded |
| Next review date | not recorded |
| Status | Indicative |
Needed before this calculator can be marked Verified: reviewer name, qualification and review date; licensed clause-by-clause standard review; exact formula reference; formula source (textbook or standard); next review date.
Formula
Worked example
| Input | Value |
|---|---|
| Required illuminance (lux) | 500 |
| Room area | 100 m² |
| Lumens per luminaire | 4,000 |
| Utilisation factor | 0.6 |
| Maintenance factor | 0.8 |
- N = 500 × 100 / (4,000 × 0.6 × 0.8) = 26.042
- Rounded up = 27
Assumptions
- Uniform layout
- Utilisation factor taken from the luminaire data for this room
Check uniformity and glare separately; the count is a starting point for layout.
Inputs and results
| Input | Unit | Allowed or shown | Note |
|---|---|---|---|
| Required illuminance (lux) | (number) | greater than 0 | |
| Room area | m² | greater than 0 m² | |
| Lumens per luminaire | (number) | greater than 0 | |
| Utilisation factor | (number) | greater than 0, up to 1 | |
| Maintenance factor | (number) | greater than 0, up to 1 |
| Result | Unit | Allowed or shown | Note |
|---|---|---|---|
| Luminaires (calculated) | (number) | Shown to 1 decimal place | |
| Luminaires (rounded up) | (number) | Shown to 0 decimal places |
How it is calculated
Each input is converted to the base unit of its quantity, the formula above is applied in the order shown in the worked example, and each result is shown in the unit you choose. Results are held at full precision and rounded only for display, except where a step selects a standard size, as the worked example shows. A value outside its allowed range is refused with a message instead of giving a result.
How the result changes with room area
| Room area (m²) | Luminaires | Luminaires |
|---|---|---|
| 10 | 2.6 | 3 |
| 25 | 6.5 | 7 |
| 50 | 13 | 14 |
| 100 | 26 | 27 |
| 200 | 52.1 | 53 |
| 400 | 104.2 | 105 |
| 1,000 | 260.4 | 261 |
Other inputs are the same as in the worked example above.
Standards and further reading
- EN 12464-1 (lighting of indoor workplaces)
- CIE publications on photometry
Lamp and luminaire data come from the manufacturer; the illuminance targets that apply come from your project specification and local regulation. These are named as background reading. Elecmetric does not embed clause text or rating tables, and the reviewer record for this calculator is separate from this list.
Frequently asked questions
What do I need to enter?
Enter required illuminance (lux), room area, lumens per luminaire, utilisation factor and maintenance factor. Change the unit of a value with its selector and the result stays the same.
What does this calculator assume?
Uniform layout. Utilisation factor taken from the luminaire data for this room.
Which calculators should I use next?
Common next steps are Appliance Running Cost (Energy and Cost) and Power from Voltage and Current. The related links at the bottom of this page open them.
How accurate are the results?
Every figure comes from the same tested engine as the Elecmetric calculators and is meant for estimating. 6 reference cases, calculated from textbook formulas coded separately from the engine by the same author, agree with this calculator. This is not an independent review. Check design values against the standard and the equipment data you work to.
Formula guides and reference
Longer explanations with worked examples and tables, written for the same topic.
- Lighting Formulas: Lux, Lumens and Candela: Lighting formulas for lux, lumens and candela: inverse square law
- Point Illuminance Formulas: Point-by-point lighting formulas: the illuminance on a horizontal plane from a luminous intensity
- Illuminance and Luminance Converter: lux, foot-candles and related units
More Lighting and Facilities calculatorsAll engineering calculatorsLighting Level (Lumen Method) in Elecmetric