ASHRAE 90.1 Lighting Power Density Allowances by Space Type

If you have ever had a lighting submittal bounced for "exceeds LPD," this is the number that did it. Lighting power density, in watts per square foot, is the cap ASHRAE 90.1 puts on how much connected lighting load a space or a building can carry. Get the space type wrong, or quote the wrong edition, and a perfectly good fixture package fails on paper.

This guide explains how 90.1 sets the number, what changed across the recent editions, where the values moved in the direction you would not expect, and how to find the figure that actually binds your project. It deliberately does not reproduce an LPD table. The standard is copyrighted, and the table in your adopted edition is the document you should be quoting on a submittal anyway.

What LPD is, and what it is not

Lighting power density is connected load divided by floor area. A 2,000 square foot open office with 1,100 W of luminaires installed is at 0.55 W per square foot. ASHRAE 90.1 sets a maximum LPD for each space type, multiplies it by the area, and the result is the lighting power allowance for that space. Your installed wattage has to come in under it.

Two things LPD is not. It is not a light level; foot candles are a separate design question, covered in our guide to reading a lighting spec sheet. And it is not the whole compliance story. Every compliance path in 90.1 requires you to meet the power limit first and then the lighting control requirements, which sit in a separate mandatory section.

The three ways to comply

Standard 90.1 gives three prescriptive routes for interior lighting power. All three come from the same lighting model; the space-by-space values are generated first and the other two are derived from them.

Building Area Method (Section 9.5.1). One LPD for the whole building based on its type. The least work of the two full methods, and usually a tighter budget than space-by-space. Note the Simplified path below is tighter still.

Space-by-Space Method (Section 9.5.2 in 90.1-2022; Section 9.6 in 90.1-2019 and earlier, where the additional allowances sit in a subsection of 9.6 - sources disagree on the sub-number, so read it off your edition). A separate LPD for every room type, summed across the building. More work, more flexibility, and it is the only path that gives access to the additional allowances for decorative, retail and videoconferencing lighting.

Simplified Building Method (Section 9.3). A short-form path for office, retail and school buildings under 25,000 square feet where those uses make up at least 80 percent of the floor area. Under 90.1-2019 it came with simpler control requirements. Addendum s moved the control requirements into a shared table whose title names the Building Area and Space-by-Space methods only, so check what your adopted edition asks of the Simplified path specifically. Addendum s does note that the space-by-space values are what generate both the Building Area and Simplified Building Method numbers.

A project picks one path. You cannot use the Building Area value for the shell and the space-by-space value for the room that needs more.

What changed between editions, and why the average misleads

ASHRAE's LPD tables are copyrighted, and we are not going to reproduce them here. What follows is what the tables do, which is the part that changes how you price a job. For the actual number against your space type, pull the edition your permit is under. Our sources are linked at the foot of this post, and any figure we do quote is given individually, in line, rather than transcribed as a set.

The values are not monotonic, in either direction. Moving from 90.1-2019 to 90.1-2022, some space types went up and others came down, and the same is true again from 90.1-2022 to Addendum s. ASHRAE attributes the moves to updated lighting recommendations, new luminaire data and revised design assumptions. Do not assume the newer document always carries the lower number. The clearest single illustration is warehouse space for medium to bulky palletized items: it sat unchanged between the 2019 and 2022 editions, then rose to 0.41 W per square foot under Addendum s, from 0.33, even though Addendum s cut space-by-space values by 6.5 percent on average (Addendum s to 90.1-2022, approved 23 July 2024). Price a warehouse job off the average and you will be wrong in the direction that costs you.

The office size breaks changed, and so did what the break is based on. The 2022 edition moved the enclosed office threshold from 250 square feet to 150 square feet. Addendum s then drops the enclosed versus open-plan distinction altogether and bands offices purely by floor area: 150 square feet or less, over 150 to 300, and over 300. Under Addendum s a 400 square foot enclosed office takes the largest-band value, not an enclosed-office value. That is a structural change, so a number you carried over from a 2019 submittal may be sitting in the wrong band entirely.

Addendum s is a set of revised values, not a new edition. It split the old combined table into two, a control requirements table now in Section 9.4 and an LPD table in Section 9.5.2, and reduced space-by-space LPDs by 6.5 percent on average. It did that by moving the lighting model's lamp lumen depreciation from 0.85 to 0.90, replacing fixed dirt depreciation factors with the IES RP-36 method, and refreshing luminaire efficacy data. Whether the addendum applies to your project depends on whether your jurisdiction adopted it, so check that before you price against it.

Tenant improvement work is where this bites most often, because a single floor can carry a dozen different space types and each one carries its own allowance. Our LED high bay guide covers how to hit the tighter numbers with modern fixtures.

The Building Area Method, and how 90.1 compares with the IECC

For the whole-building path, the Smart Energy Design Assistance Center at the University of Illinois, an Illinois state energy code training provider, published a building-type comparison of 90.1-2019 against the 2018 IECC. The useful finding is directional: across the building types it compares, 90.1-2019 is the tighter of the two for most of them, and in some cases by a wide margin. An office building is the representative case, allowed 0.64 W per square foot under 90.1-2019 against 0.79 under the 2018 IECC. Libraries run the other way, with the IECC slightly tighter. If your jurisdiction lets you comply under either document, that gap is worth checking before you choose, and the full comparison is in the source linked below.

ASHRAE says its 2022 edition trimmed interior LPD values by about 4 percent overall compared with 2019 - a figure it gives for interior LPD as a whole, not for the Building Area table specifically - and Lighting Controls Academy reports the 2025 edition takes Building Area values down another 5 to 10 percent for most building types, with warehouses the exception. We have not read the 2025 table ourselves, so treat those as directional and pull the edition your permit is under.

Additional allowances under the Space-by-Space Method

Section 9.5.2.2 lets you add lighting power on top of the space value for specific purposes. The figures below are the 90.1-2022 values, confirmed against ASHRAE's own published summary of the 2022 lighting changes; Addendum s restruck the cross-references in this section but did not revise the values:

  • Decorative lighting: 0.70 W per square foot, down from 0.75 in 2016 and 2019. Lighting Controls Academy reports the 2025 edition cuts this again to 0.50.
  • Retail sales: a base wattage plus a per-square-foot allowance that varies by merchandise category, from 0.40 W per square foot for the lowest two categories up to 1.00 for the highest. All four category figures were cut from their 2019 values, and so was the base wattage. The category definitions and the base wattage are in the standard's own table; quote that on a submittal rather than a summary.
  • Videoconferencing: new in 2022, 0.50 W per square foot for rooms that meet ANSI/IES/AVIXA RP-38-17.

The 2025 edition also adds a 1.0 W per square foot allowance for interior exit stairways. That is reported by Lighting Controls Academy, not read from the standard by us, and we have not confirmed the reason for it.

The additional allowances do not apply to the Building Area or Simplified paths. That is the main reason retail and hospitality projects go space-by-space.

The room geometry adjustment

Tall, narrow rooms need more power to hit the same light level, and 90.1 accounts for it. Most space-by-space entries carry a room cavity ratio, RCR, alongside the LPD; a few carry a different test or none at all. If your room's actual RCR exceeds the table value, the standard lets you increase that space's LPD by 20 percent. The RCR formula is 2.5 times the room cavity height times the perimeter, divided by the floor area, where cavity height is luminaire mounting height minus workplane height.

A 40 by 40 foot classroom with an 8 foot cavity has a perimeter of 160 feet and an area of 1,600 square feet, so 2.5 x 8 x 160 / 1,600 gives an RCR of 2.0, still under the table value of 4, so no adjustment. (A widely circulated state training deck works this same example and prints 0.5, having substituted the 40 foot side length for the 160 foot perimeter. Use the perimeter.) An 80 by 15 foot room with a 32 foot cavity calculates to 12.67, and the extra 20 percent applies. Worth running on any high-ceiling shop or storage space before you conclude the budget cannot be met. Corridors are the exception: they qualify for the adjustment on width under 8 feet rather than on an RCR value, so do not run the formula on one.

Rules that decide whether LPD applies at all

Alterations. The 2022 edition set firm thresholds. Replace 2,000 W or more of existing interior lighting and the project has to meet all of Section 9. Replace less than 2,000 W and the new lighting still has to meet the Section 9.4.1 lighting control requirements, and either use 50 percent less power than the system it replaces or comply with the Space-by-Space method. Below the threshold is a reduced path, not an exemption, and the controls are owed either way. Exterior work triggers full compliance at more than 10 luminaires or more than 20 linear feet of luminaires replaced.

Track lighting. For line-voltage track without a specified wattage, 90.1-2022 assumes 10 W per linear foot, down from 30 W per linear foot in earlier editions. That change alone can move a retail job from failing to passing.

Exempt equipment. Table 9.2.2.1 lists lighting that is left out of the LPD calculation, such as the germicidal function of a UV disinfection luminaire (the general lighting portion of a dual-function fixture still counts). The exemptions do not apply to the Simplified path. The 2022 edition removed the old casino and parking garage daylight transition zone exemptions and gave both their own LPD values instead.

LPD is half the job: the controls that come with it

Every space type in 90.1 also carries a control requirement, and Addendum s put those in their own table in Section 9.4, which the addendum's foreword says makes clear they apply when using both the Building Area Method and the Space-by-Space Method. The ones that most often catch a fixture-only submittal:

  • Multilevel control means a manual dimmer running from full down to 10 percent or less; bi-level switching alone stopped satisfying this in 2022. Lighting Controls Academy lists offices, dining areas and lounges or breakrooms among the spaces where it is required; the space list should be read off the edition your jurisdiction adopted.
  • Open offices over 300 square feet need occupancy control zoned at no more than 600 square feet under 2022. Lighting in an unoccupied zone may come on to no more than 20 percent when a neighboring zone is occupied. Lighting Controls Academy reports the 2025 edition changes the zoning to an average of 600 square feet per sensor with no single zone over 900 square feet.
  • Daylight-responsive control is triggered at 75 W of general lighting in the primary sidelit zone and 150 W at the secondary threshold under 2022. For context on the size of that change: 90.1-2019 required photocontrols at 150 W in the primary sidelighted area and 300 W across primary and secondary combined, so 2022 halved both. Lighting Controls Academy reports 2025 drops the secondary threshold to 75 W as well.
  • Occupancy timeouts: Lighting Controls Academy reports 20 minutes in 2022, reduced to 15 minutes in 2025.

Our commercial lighting controls buyer's guide and occupancy sensor buying guide walk through the hardware side. If your project is in California, the daylighting rules differ; see Title 24 daylighting requirements.

Which edition applies to your project

Standard 90.1 is a model standard. It only binds you when a jurisdiction adopts it, either directly or through the IECC, which lists 90.1 as an alternative compliance path.

The federal reference point is 90.1-2022. The U.S. Department of Energy issued its determination on 6 March 2024 that the 2022 edition improves energy efficiency, which started the two-year clock for states to certify that their commercial codes meet or exceed it; that deadline was 6 March 2026. Many states are still on 2021 IECC (which references 90.1-2019) or earlier, and a few adopt 90.1 directly with local amendments.

90.1-2025 has been published. Lighting Controls Academy reports it incorporates 105 addenda and reorganized the lighting requirements; we have not confirmed which addenda it folds in, so we make no claim that the Addendum s table restructure carried through. Adoption typically trails publication, so the edition in force for your permit is likely to be an earlier one. Ask the authority having jurisdiction which edition and which addenda apply, then quote that document's table on the submittal, not a summary. Our comparison of ASHRAE 90.1 and California Title 24 explains why California projects are a different case entirely.

Meeting the budget without under-lighting the space

The practical path to LPD compliance in 2026 is fixture efficacy. Check the delivered lumens and the input watts on the spec sheet and work the math for your own space rather than assuming a fixture clears the budget. Take particular care with any office value you are working to: the tightest of the current office numbers comes from Addendum s, so it only binds you if your jurisdiction adopted the addendum, and pricing against it where it was not adopted means over-specifying. Our LED troffer and panel guide covers the backlit versus edge-lit decision and the efficacy numbers to look for.

Rock Lighting and Electric stocks the fixtures and controls this section of the code is written around. Browse troffers, the wider interior lighting range, and lighting controls for the dimming and occupancy hardware. If you have a lighting schedule and an LPD problem, send us the takeoff and we will price a package that lands under the allowance. Contractors buying regularly should open a contractor account for project pricing, or contact us if the space type does not fit a standard table entry.

Related guides

FAQ

What is lighting power density in ASHRAE 90.1?
Lighting power density, or LPD, is the maximum connected interior lighting load a space or building may carry, expressed in watts per square foot. ASHRAE 90.1 multiplies the LPD for a space type by its floor area to produce a lighting power allowance, and the installed lighting wattage must not exceed it. It is a power cap, not a light level requirement.
What is the ASHRAE 90.1 LPD for an office?
It depends on the edition, the method and the size of the room, and there is no single headline number. Under the Building Area Method, 90.1-2019 allows 0.64 W per square foot for an office building. Under the Space-by-Space Method the answer is banded: the 2019 and 2022 editions both separate enclosed from open-plan offices and band enclosed offices by size, with the 2022 edition moving that break from 250 square feet to 150 square feet, while Addendum s to 90.1-2022 drops the enclosed versus open-plan distinction entirely and bands offices purely by floor area at 150 square feet or less, over 150 to 300, and over 300. Read the value off the edition your permit was pulled under, in the band your room actually falls in.
What is the difference between the Building Area Method and the Space-by-Space Method?
The Building Area Method applies one LPD to the whole building based on its primary use and is the simplest path. The Space-by-Space Method assigns an LPD to each room type and sums them, which takes more work but usually yields more total power and is the only path that permits the additional allowances for decorative, retail and videoconferencing lighting. A project must use one method throughout.
Did ASHRAE 90.1-2022 lower lighting power densities?
On average, yes, by about 4 percent for interior LPDs compared with 90.1-2019, according to ASHRAE's published summary of the 2022 lighting changes. But the average hides the detail: individual space types moved in both directions, with meeting and open-office spaces coming down while some classroom and circulation spaces went up slightly. Addendum s, approved by the ASHRAE Standards Committee in June 2024, then reduced space-by-space values by a further 6.5 percent on average, and even there at least one space type rose rather than fell. Check your own space type against the table rather than applying the average.
Can I add lighting power for decorative or retail lighting under ASHRAE 90.1?
Only under the Space-by-Space Method. Section 9.5.2.2 of 90.1-2022 allows 0.70 W per square foot for decorative lighting, a retail allowance of a base wattage plus 0.40 to 1.00 W per square foot depending on the merchandise category, and 0.50 W per square foot for videoconferencing rooms meeting RP-38-17. Lighting Controls Academy reports the 2025 edition reduces the decorative allowance to 0.50 W per square foot.
Does replacing fixtures in an existing building trigger ASHRAE 90.1 LPD limits?
Under 90.1-2022, replacing 2,000 W or more of existing interior lighting means the project has to meet all of Section 9, including the LPD limit. Below 2,000 W the alteration still owes the Section 9.4.1 lighting control requirements, and either has to use 50 percent less power than the lighting it replaces or comply with the Space-by-Space method. It is a reduced path, not an exemption. Confirm the alteration rules for the edition your jurisdiction has adopted; earlier editions worded the threshold differently.

Sources

This article is general guidance, not a substitute for the manufacturer’s current documentation or the adopted code for your project. Confirm specifications, compatibility, and code requirements for your specific application before purchase or installation.

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