# Lighting Power Density: Watts per Square Metre

> Lighting power density (LPD) is the installed lighting load divided by floor area, in watts per square metre. Energy codes such as ECBC 2017 set maximum LPD values by building type, so the lighting design has to hit its lux targets within a power budget.

## Why it matters

LPD is where lighting design meets the energy code. A scheme can look fine on a
lux plot and still fail compliance if it uses too much power to get there.

## How it works in practice

| Factor | Effect on LPD |
| --- | --- |
| Fitting efficacy | Higher lumens per watt lowers LPD |
| Optics | Better light distribution needs fewer fittings |
| Target lux | Higher targets need more power |
| Controls | Reduce energy used, often credited by codes |

## Common mistakes

- **Adding fittings to fix dark spots.** Improve layout and optics first.
- **Over-lighting circulation.** Corridors do not need desk-level lux.
- **Ignoring daylight.** Perimeter zones can be dimmed for much of the day.

## Standards referenced

Lighting power density under **ECBC 2017**. Illumination levels under
**IS 3646**.

## Frequently asked questions

### Is LPD hard to meet with LED lighting?

Generally no — efficient LED fittings make LPD limits achievable for most offices. The limit mainly stops a design that solves every dark area by adding more fittings, and it rewards good optics and layout.

### Do lighting controls help?

Yes. Daylight-linked dimming near windows and occupancy sensing in meeting rooms and toilets reduce actual energy use, and codes often credit them.

## Sources

- [ECBC 2017](https://beeindia.gov.in/) — Lighting power density
- [IS 3646](https://standards.bis.gov.in/website/published-standards/department-wise) — Interior illumination

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Source: https://hagerstone.com/glossary/lighting-power-density