Why is the answer bigger than the spacing calculation gives?

Because BS 5266-1 requires luminaires at places the spacing grid knows nothing about. A luminaire is needed at each exit door and outside each final exit, at each flight of stairs so the flight itself receives direct light, at every change of direction and every change of level, at corridor intersections, and at fire alarm call points and firefighting equipment. These are where people stop, turn or reach for something in the dark, and none of them cares how the spacing worked out. A corridor that computes as four luminaires routinely installs as seven, which is one of the most common under-quotes on a small emergency lighting job.

Is an average of 1 lux good enough?

No, and this is the distinction that matters most on the page. EN 1838 sets 1 lux as a MINIMUM on the centre line of the escape route, not an average across it. A corridor averaging five lux can still have a 0.2 lux hole between two widely spaced fittings, and the hole will be where the light from neither reaches — often exactly at a turn or a stair head. That is also why the standard limits the maximum-to-minimum ratio along the centre line to 40:1: an even one lux is safe to walk, and a bright patch beside a dark one is worse than either, because eyes adapting to the bright part cannot see into the dark part at all.

Where does the spacing ratio come from?

The luminaire's own data sheet. Every emergency fitting is published with a spacing table derived from its photometric file, listing the axial and transverse spacing that still delivers one lux at a given mounting height. It is a property of that fitting's light distribution, so it varies enormously: a bulkhead throwing light along a corridor can exceed six times its mounting height, and a decorative fitting that puts most of its output on the ceiling can be under two. The default here is a placeholder for an ordinary recessed emergency downlight and should be replaced with the real figure before anything is ordered.

Does this cover an open area or a plant room?

No — it covers escape routes up to 2 m wide, which is one of three cases EN 1838 treats separately. An open or anti-panic area needs 0.5 lux over the empty floor while EXCLUDING a border 0.5 m wide around it, which is a different geometry rather than a different number. A high-risk task area needs 10% of the maintained illuminance the task normally gets, with a floor of 15 lux, because the point there is not escaping but shutting something down safely first.

How long do they have to stay lit?

One hour or three, and the layout does not decide it — the battery does. Three hours is usual where the premises sleeps people, where evacuation may be phased, or where the building will not be re-occupied until the supply is restored; one hour suits a premises that empties quickly and can be checked before anyone returns. It is worth settling early, because the duration changes the battery and therefore the fitting, and the fitting is what carries the spacing ratio this calculation depends on.

Electrical

Emergency Escape Lighting Spacing Calculator

How many emergency luminaires an escape route needs: the spacing that holds EN 1838's minimum on its centre line, plus one at each point of emphasis.

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Imperial · sales tax

Escape route length

The length of the escape route this run of luminaires covers.

Measure along the route people will actually walk, not in a straight line across the plan. A corridor that turns twice is longer than the diagonal, and the turns themselves each need a luminaire — count them below.

Mounting height

Height of the luminaire above the floor.

Higher mounting spreads light further, so the spacing grows with it — but the illuminance at any one point falls, which is why the ratio below is published per fitting rather than being a constant. Below about 2 m a luminaire is in the way of people and in the line of sight, and EN 1838's glare limits tighten.

Spacing-to-height ratio at 1 lux

From the luminaire's own spacing table — how many times its mounting height it may be spaced.

Every emergency luminaire is sold with a spacing table derived from its photometric file, giving the axial and transverse spacing that still delivers 1 lux at a stated mounting height. Four is a reasonable figure for an ordinary recessed emergency downlight and is only a placeholder: a bulkhead with a wide distribution can exceed six, and a decorative fitting with most of its output on the ceiling can be under two. Use the number on the data sheet for the fitting you are actually buying.

Points of emphasis on this route

Exits, stair flights, changes of direction and level, call points and firefighting equipment.

BS 5266-1 requires a luminaire near each of these whatever the spacing calculation says, because they are where people stop, turn, or reach for something. Count every one on this route: each exit door and the outside of each final exit, each flight of stairs, every change of direction and change of level, each corridor intersection, each fire alarm call point and each piece of firefighting equipment. Two of them close together share one luminaire, so count positions rather than items.

Emergency luminaires required

8 luminaires

Medium confidence

This holds 1 lux (0.09 fc) on the centre line of a route up to 2 m (6.5 ft) wide, using the spacing ratio you entered. That ratio is the whole calculation — it belongs to a specific fitting at a specific mounting height, and taking it from a different luminaire's data sheet invalidates the answer.

Maximum spacing at this height and ratio: 32 ft
Actual spacing once the run is divided evenly: 24.5 ft
Luminaires from spacing alone: 5 fittings
Added for points of emphasis: 3 fittings

Then change the inputs to see how far the answer moves.

Show calculation logic

How this was calculated

Formula source(s)

EN 1838 / BS 5266-7, Lighting applications — emergency lighting: escape routes up to 2 m wide require a minimum of 1 lux on the centre line, with uniformity along that line no worse than 40:1
BS 5266-1, Code of practice for the emergency escape lighting of premises: a luminaire is required at each exit door, at each stair flight so every flight receives direct light, at every change of direction and change of level, at intersections of corridors, outside each final exit, and at fire alarm call points and firefighting equipment — conventionally within 2 m horizontally of each
Spacing is taken as the mounting height multiplied by the luminaire's published spacing-to-height ratio for the target illuminance; that ratio comes from the manufacturer's photometric data and is specific to the fitting

Inputs used

Escape route length: 98 ft
Mounting height: 8 ft
Spacing-to-height ratio at 1 lux: 4
Points of emphasis on this route: 3

Intermediate steps

Maximum spacing at this height and ratio: 32 ft
Actual spacing once the run is divided evenly: 24.5 ft
Luminaires from spacing alone: 5 fittings
Added for points of emphasis: 3 fittings

Final result8 luminaires

Confidence note: This holds 1 lux (0.09 fc) on the centre line of a route up to 2 m (6.5 ft) wide, using the spacing ratio you entered. That ratio is the whole calculation — it belongs to a specific fitting at a specific mounting height, and taking it from a different luminaire's data sheet invalidates the answer.

What this calculation does not cover

Escape routes only, up to 2 m (6.5 ft) wide. An open area needs 0.5 lux (0.05 fc) over the empty floor EXCLUDING a 0.5 m (1.6 ft) border, and a high-risk task area needs 10% of its normal maintained illuminance or 15 lux (1.4 fc), whichever is greater — both are different calculations.
Does not check uniformity. EN 1838 limits the ratio of maximum to minimum illuminance along the centre line to 40:1, and a run that meets the minimum at every point can still fail that if the fittings are unevenly placed.
Does not address duration, which is the other half of the specification: one hour or three depending on the premises and how it is evacuated, and it is the battery rather than the layout that delivers it.
Does not check disability glare, which limits luminous intensity within the field of view and bites hardest on high mounting in a low-ceilinged space.

Estimated cost — your price

Price per luminaire ($)

This site holds no price list for this material — local prices vary too much to publish honestly. Enter your supplier's price and the result is costed with it.

Schematic, drawn to the proportions you entered — not to scale on screen.

Computed in your browser — nothing you enter is uploaded. Presented in US customary units and US trade terminology. Where a formula follows a published standard, that standard and its edition are cited beside it on this page; where none governs, the page says so. Local amendments override model codes — verify against the code in force where you build.

Sources checked 2026-09-02 · in the site-wide review of 2026-09-06 · v1.0.1

Regulatory standards & verification citations3

EN 1838 / BS 5266-7, Lighting applications — emergency lighting: escape routes up to 2 m wide require a minimum of 1 lux on the centre line, with uniformity along that line no worse than 40:1
BS 5266-1, Code of practice for the emergency escape lighting of premises: a luminaire is required at each exit door, at each stair flight so every flight receives direct light, at every change of direction and change of level, at intersections of corridors, outside each final exit, and at fire alarm call points and firefighting equipment — conventionally within 2 m horizontally of each
Spacing is taken as the mounting height multiplied by the luminaire's published spacing-to-height ratio for the target illuminance; that ratio comes from the manufacturer's photometric data and is specific to the fitting

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Still deciding? Emergency Lighting vs Normal Illuminance — the factors that actually differ, with no invented prices.

How to calculate emergency escape lighting spacing in 5 steps

Escape route lengthThe length of the escape route this run of luminaires covers.
Mounting heightHeight of the luminaire above the floor.
Spacing-to-height ratio at 1 luxFrom the luminaire's own spacing table — how many times its mounting height it may be spaced.
Points of emphasis on this routeExits, stair flights, changes of direction and level, call points and firefighting equipment.
Emergency luminaires requiredThe tool computes the emergency luminaires required from those figures and shows the formula, its sources, and a confidence rating alongside it.

Frequently asked questions

Why is the answer bigger than the spacing calculation gives?: Because BS 5266-1 requires luminaires at places the spacing grid knows nothing about. A luminaire is needed at each exit door and outside each final exit, at each flight of stairs so the flight itself receives direct light, at every change of direction and every change of level, at corridor intersections, and at fire alarm call points and firefighting equipment. These are where people stop, turn or reach for something in the dark, and none of them cares how the spacing worked out. A corridor that computes as four luminaires routinely installs as seven, which is one of the most common under-quotes on a small emergency lighting job.
Is an average of 1 lux good enough?: No, and this is the distinction that matters most on the page. EN 1838 sets 1 lux as a MINIMUM on the centre line of the escape route, not an average across it. A corridor averaging five lux can still have a 0.2 lux hole between two widely spaced fittings, and the hole will be where the light from neither reaches — often exactly at a turn or a stair head. That is also why the standard limits the maximum-to-minimum ratio along the centre line to 40:1: an even one lux is safe to walk, and a bright patch beside a dark one is worse than either, because eyes adapting to the bright part cannot see into the dark part at all.
Where does the spacing ratio come from?: The luminaire's own data sheet. Every emergency fitting is published with a spacing table derived from its photometric file, listing the axial and transverse spacing that still delivers one lux at a given mounting height. It is a property of that fitting's light distribution, so it varies enormously: a bulkhead throwing light along a corridor can exceed six times its mounting height, and a decorative fitting that puts most of its output on the ceiling can be under two. The default here is a placeholder for an ordinary recessed emergency downlight and should be replaced with the real figure before anything is ordered.
Does this cover an open area or a plant room?: No — it covers escape routes up to 2 m wide, which is one of three cases EN 1838 treats separately. An open or anti-panic area needs 0.5 lux over the empty floor while EXCLUDING a border 0.5 m wide around it, which is a different geometry rather than a different number. A high-risk task area needs 10% of the maintained illuminance the task normally gets, with a floor of 15 lux, because the point there is not escaping but shutting something down safely first.
How long do they have to stay lit?: One hour or three, and the layout does not decide it — the battery does. Three hours is usual where the premises sleeps people, where evacuation may be phased, or where the building will not be re-occupied until the supply is restored; one hour suits a premises that empties quickly and can be checked before anyone returns. It is worth settling early, because the duration changes the battery and therefore the fitting, and the fitting is what carries the spacing ratio this calculation depends on.

Preliminary estimate, not certified engineering. This tool produces an indicative quantity calculation for planning purposes only — it is not a certified structural analysis, a guaranteed material takeoff, or a substitute for building department approval. Always verify measurements on-site and have a licensed contractor or structural engineer review any load-bearing, code-sensitive, or safety-critical work before purchasing materials or starting construction. Spotted an arithmetic or standards error? Report it to contact@craftquantities.com with your inputs — a confirmed fix gets a permanent check of its own, so the same mistake cannot come back.