Lighting an Egress Stair: The 10 lx Rule and What It Means for the Steel
Emergency lighting requirements for exit stairs in BC, the 10 lx average at tread level, and how lighting decisions change stair fabrication and guard detailing.
Emergency lighting is an electrical scope that quietly constrains a steel scope. The stair usually finds out last.
This article is fabrication context, not engineering or permit advice. Code interpretation belongs with the authority having jurisdiction (AHJ) and the project’s licensed professionals. Confirm applicability with the local building department before finalizing design or permit submissions.
Emergency lighting is an electrical scope that quietly constrains a steel scope. The stair usually finds out about it last, and by then the steel is coated.
The requirement is measured at the tread, not the fitting
Clause 3.2.7.3.(1)(a) of the BC Building Code requires exits to be illuminated under emergency power to an average level of not less than 10 lx at floor or tread level. The BC Building Code Interpretation Committee and appeal decisions such as BCAB 1227 address how the emergency lighting and exit sign provisions apply in practice.
Two words in that requirement do the work. “At tread level” means the measurement is taken where people put their feet, not at the fitting, so anything that blocks or absorbs light between the source and the tread matters. “Average” means the requirement is about distribution across the stair rather than about a single fixture’s output, which is why fitting layout is the design problem rather than fitting selection.
These are Part 3 provisions, so they apply to buildings covered by Part 3 rather than to most housing. Which part governs a given building is a classification question for the designer and the AHJ.
Averages hide the places people actually trip
A distribution that averages correctly can still be poor where it matters.
The awkward points on a stair are consistent: the top riser, the bottom riser, the nosing line generally, and the turn at a landing. Those are where a foot placement error has consequences, and they are also where a stair casts shadows on itself. A flight lit from above throws the shadow of each nosing onto the tread below it, which reduces contrast exactly at the edge people need to see.
This is why lighting an egress stair well is a different exercise from meeting a number. Light that arrives along the flight, or from low down at tread level, reveals the nosings. Light that arrives straight down from a landing ceiling can average acceptably and still leave the nosing line indistinct.
That interacts with how the treads are finished. The visibility of the step edge is partly a lighting question and partly a contrast question, and the two get designed together. The contrast side is covered in stair nosing profiles.
Finish changes the result more than people expect
The same fittings over two different stairs do not produce the same light at tread level.
A dark powder-coated stringer with dark treads absorbs a large share of the light that hits it. A galvanized stair with pale concrete-filled treads reflects a good deal of it back into the space, including onto adjacent surfaces. The difference is not marginal.
For a designer working to an average at tread level, that means the finish schedule is an input to the lighting calculation rather than a decoration decided afterwards. Where a project changes from a light finish to a dark one late in design, which happens regularly, the lighting design may no longer deliver what it was calculated to deliver. Worth flagging in both directions: the electrical designer should know the finishes, and the person changing the finishes should know it affects the lighting.
Emergency and decorative lighting are different systems
This confusion causes real problems at inspection, and it is easy to avoid.
Emergency lighting is on emergency power and exists to keep an exit usable when normal power fails. Decorative or architectural stair lighting is on normal power and exists because the stair looks better lit. They frequently occupy the same stair and sometimes the same physical locations, but only one of them satisfies the code requirement.
A beautifully lit stair with LED strips in the stringers can therefore still fail an emergency lighting check, because those strips go dark with everything else. Conversely, an emergency fitting does not have to be attractive, which is why the two systems are usually designed separately and coordinated physically. The decorative side is covered in LED stair lighting integration.
Where the fittings go is a steel question
Here is the point at which an electrical scope becomes a fabrication scope.
If fittings are mounted to the building, the stair is unaffected. If they are mounted to the stair, which is increasingly the case for stringer-integrated and handrail-integrated lighting, then the steel has to be fabricated to receive them. That means a housing or a recess, a route for the cable, a penetration where the cable enters and exits, and access for maintenance and lamp replacement.
Every one of those is straightforward while the stair is being fabricated and difficult afterwards. Drilling a coated stringer damages the coating. Welding a bracket to a galvanized assembly burns the zinc off locally. Running a cable through a closed section that has no access point is not possible without cutting it open.
In our shop, the projects that go smoothly are the ones where the electrical drawings arrive with the architectural ones. A stair that has already been through the finishing process is the wrong moment to discover that four fittings are meant to be recessed into its stringers.
Handrail lighting has to respect the handrail
An integrated handrail light is an appealing solution, because it puts light exactly where it is needed and it is naturally at the right height.
It also has to remain a handrail. The requirement that a handrail be continually graspable along its entire length with no obstruction on or above it to break a handhold does not relax because a light has been added. A fitting that projects, a lens that interrupts the grip surface, or a housing that widens the profile can all compromise that.
The detail that usually works is a light emitting downward from beneath the rail, or from a slot in a profile whose graspable surface remains uninterrupted. It needs to be drawn in section rather than assumed, for exactly the reasons set out in handrail graspability.
Coordination is a general contractor task, not a fabricator one
It is worth being clear about who owns what, because this scope falls between trades more often than most.
The electrical designer owns the light levels and has to demonstrate compliance. The fabricator owns the steel and supplies the physical provisions: mounting points, penetrations, routes, access. Neither can do the other’s job, and neither usually sees the other’s drawings unless somebody arranges it.
That arrangement is the general contractor’s task, and it is a small one if done early. The information the fabricator needs is short: which fittings are mounted on the stair, where, how they fix, how the cable gets to them, and what finish the stair is receiving. Sent with the architectural package, it costs nothing. Sent after fabrication, it costs a stair being reworked.
Maintenance access is part of the design
A fitting integrated into a stair has to be serviceable, and this gets designed out surprisingly often.
Lamps fail, drivers fail, and lenses get damaged. A light recessed into a stringer with no access panel, or a fitting behind a welded cover plate, becomes a maintenance problem the moment it stops working. On an emergency lighting fitting that problem is more than cosmetic, because the system has to keep functioning to satisfy its purpose.
The design questions are straightforward and belong in fabrication. Can the fitting be removed from the front, or does something have to come apart. Is there room to withdraw the fitting and disconnect it. Where does the cable have enough slack to allow that. Is the access point somewhere a technician can reach from the stair itself, or does it need equipment.
Emergency lighting also typically requires periodic testing, which means somebody visits the fittings on a schedule rather than only when one fails. A design that makes testing awkward gets tested less thoroughly, which is a quiet way for a compliant installation to become a non-functioning one.
For a fabricator this translates into a small number of concrete provisions: removable cover plates rather than welded ones, cable slack at each fitting, and access points positioned where they can be reached. None adds meaningful cost during fabrication, and all of them are effectively impossible to add afterwards.
What to send with the stair enquiry
Add four documents to the usual package and this scope stops being a risk.
The electrical drawings showing any fitting mounted on or adjacent to the stair, the conduit routing near the stair, a note of which fittings are on emergency power, and the finish schedule for the stair and treads. Those four let the mounting provisions be designed into the steel and let the lighting designer calculate against the finishes that will actually be installed. The broader coordination picture is in commercial staircase design.
Sources
- BC Building Code Interpretation Committee, emergency lighting interpretation, BOABC
- BCAB 1227, Emergency Lighting and Exit Signs, Province of British Columbia
- BC Building Code 2018, Division B, Section 3.4: Exits
Lighting is the scope most likely to arrive at a stair after the stair is finished. Ask for the electrical drawings at the same time as the architectural ones, and the fittings get built into the steel rather than drilled into it.
Related questions
What light level does an exit stair need under emergency power?
Clause 3.2.7.3.(1)(a) of the BC Building Code requires exits to be illuminated under emergency power to an average level of not less than 10 lx at floor or tread level. The measurement is taken at the walking surface, not at the light fitting.
Is that an average or a minimum everywhere?
The provision is written as an average level, which is why the layout of fittings matters as much as their output. An average can be met while individual points on the stair sit lower, so a designer works to the distribution rather than to a single fixture specification.
Does this apply to a house?
These are Part 3 provisions applying to buildings covered by Part 3. Housing and small buildings are covered by Part 9, which has its own lighting requirements. Confirm which part governs your building with the designer and the authority having jurisdiction.
Why does emergency lighting affect stair fabrication?
Because fittings and conduit have to go somewhere, and on a steel stair that somewhere is often the guard, the stringer, or the underside of a landing. Mounting points and cable routes are much easier to build into the steel than to add to a coated, installed stair.
Can lighting be integrated into the stair itself?
Yes, and it is increasingly common. Fittings recessed into stringers, mounted under a handrail, or set into the guard can deliver light at tread level cleanly. Any of those means the steel has to be fabricated with the housing, the cable route, and access for maintenance.
Does integrated lighting count toward the emergency requirement?
Only if it is on emergency power and the design demonstrates the required level. Decorative stair lighting on normal power is a separate system. The two often coexist, and confusing them is a common source of a late problem at inspection.
Who is responsible for proving the light level?
The electrical designer, not the stair fabricator. What the fabricator supplies is the physical provision: mounting points, penetrations, and cable routes to suit that design. Getting the two coordinated is the general contractor's task.
What happens if the lighting design changes late?
If the change moves fittings onto the stair, it usually means drilling, welding, or cutting a finished assembly. In most of the projects we see, a late lighting change is one of the more disruptive things that can happen to a fabricated stair after finishing.
Does lighting interact with the handrail?
It can. A handrail with an integrated light is an attractive solution because it puts light exactly where it is useful, but the handrail still has to satisfy graspability, and a fitting or a lens must not break the handhold. That is a detail worth drawing carefully.
Do exit signs affect the stair scope?
Occasionally. Where a sign or its conduit is mounted to stair structure rather than to the building, the fabricator needs to know the location and the fixing. It is a small item that is easy to accommodate in advance and awkward afterwards.
Does the stair finish affect how much light is needed?
In practice, yes. A dark powder-coated stair with dark treads reflects less light than a galvanized stair with pale concrete treads, so the same fittings produce a different result at tread level. The electrical designer should know the finishes.
What should a GC send the fabricator?
Send the electrical drawings showing fittings mounted on or near the stair, the conduit routing, the emergency lighting scope, and the finish schedule. Those let the mounting points and cable routes be built into the steel rather than added to it.
