What is lighting power density?

Lighting power density, or LPD, is the installed lighting wattage of a space divided by its floor area, expressed in watts per square foot. Energy codes cap it so buildings do not install more lighting power than necessary, which directly limits lighting energy use.

Which ASHRAE allowances does this use?

It uses the ASHRAE 90.1-2022 building-area method allowances from Table 9.5.1, such as 0.64 W/ft² for offices and 0.84 for retail. These are whole-building averages; the space-by-space method in Table 9.6.1 sometimes permits more in specific room types.

Should I use installed or connected wattage?

Use the installed power of the luminaires — the total input wattage of each fixture including drivers and ballasts, multiplied by quantity. For LED fixtures use the rated input watts, not the bare LED-board wattage, so the figure reflects what the panel actually serves.

Are any lights exempt from the LPD limit?

Yes. ASHRAE 90.1 Section 9.1 exempts certain lighting such as specialized medical, theatrical, and some display and emergency lighting. Exclude exempt fixtures from the total so they do not inflate the installed density and cause a false failure.

Does passing this guarantee code compliance?

No. LPD is one requirement among several — controls, daylighting, and exterior lighting also apply. The adopted energy code may be the IECC rather than ASHRAE 90.1, and editions and local amendments differ, so confirm the version in force with the authority having jurisdiction.

What is the Lighting Power Density (LPD) Calculator?

Sums installed fixture wattage per space, divides by floor area to compute lighting power density in W/ft², and compares it against ASHRAE 90.1-2022 building-area method allowances for energy-code compliance on commercial lighting designs. It runs free in your browser on Gera Tools, with nothing uploaded.

Lighting Power Density (LPD) Calculator

Name: Lighting Power Density (LPD) Calculator
Creator: Gera Tools
License: https://creativecommons.org/licenses/by/4.0/

Get one useful tool a week

Like this tool? Enter your email and we'll send you one genuinely useful Gera tool a week — plus a link to come back to this one. No spam, one-click unsubscribe any time.

Why LPD compliance matters

Energy codes limit how much lighting power a building may install, measured as watts per square foot (W/ft²). Stay under the limit and the lighting design passes plan review; exceed it and the plans bounce back for redesign. This calculator totals the installed fixture wattage for a space, divides by the floor area, and compares the result against the ASHRAE 90.1-2022 building-area-method allowance for the building type you select.

How it works

The formula is:

LPD (W/ft²) = total installed lighting power (W) / floor area (ft²)

Total installed power is the sum across every fixture type of quantity × input watts per fixture. The tool looks up the allowance for the selected occupancy from ASHRAE 90.1-2022 Table 9.5.1, computes the allowed wattage (allowance × area), and shows the remaining budget in watts — how much headroom is left before you exceed the limit.

ASHRAE 90.1-2022 allowances (building-area method, selected types)

Building type	LPD allowance (W/ft²)
Office	0.64
Retail	0.84
Warehouse	0.33
Restaurant (eating/drinking)	0.89
Hotel/motel	0.87
Hospital/healthcare	1.05
School/university	0.72
Manufacturing	0.82

These values are for the building-area method. The space-by-space method (Table 9.6.1) is calculated room by room and sometimes allows higher densities in specific spaces like operating rooms or display areas. Always verify which method is permitted by your local authority.

Worked example

A 2,000 sq ft office with 20 recessed 32 W troffers and 10 recessed 12 W downlights:

Fixture	Qty	Watts each	Total
LED troffer	20	32 W	640 W
LED downlight	10	12 W	120 W
Total installed			760 W

LPD = 760 ÷ 2,000 = 0.38 W/ft² — well under the 0.64 W/ft² office allowance, leaving 520 W of budget before you would hit the limit.

Common mistakes to avoid

Use fixture input watts, not bare LED chip ratings. The wattage that counts for code is the luminaire’s total input draw including the driver. A fixture marketed as a “20 W LED equivalent” may draw 18 W or 24 W at the wall — pull the spec sheet.

Exclude exempt lighting. ASHRAE 90.1 Section 9.1 exempts certain specialized lighting including theatrical, medical procedure, and some display lighting. Including exempt fixtures inflates your calculated LPD and may cause a false failure.

Know which code is adopted. Some jurisdictions adopt the IECC rather than ASHRAE 90.1, and the two can differ in allowances and methods. Confirm with the authority having jurisdiction before finalising the design.