Emergency lighting lux levels: how to check them with a lux meter

What is an emergency lighting lux check?

It's a set of light readings, in lux, taken on the floor at planned points while only the emergency lighting is on, together with a record of how and where each one was taken. It answers one question: how much light do the emergency luminaires actually put where people need to walk?

A lux check is not the duration test

Emergency lighting gets three different checks, and they answer different questions:

• The function test. A short switch to battery to see that every emergency luminaire comes on. It's routine maintenance and it takes no readings.
• The duration test. The system runs on battery for its full rated duration, to show the batteries last. HSE's HSG38 notes that battery escape lighting is usually designed to run for one to three hours.
• The lux check. Readings of the light the emergency luminaires give, at points along the routes and across the areas. This is the check this page covers.

The two that involve time are easy to confuse. A battery luminaire is brightest soon after it switches over and dims as the battery runs down, and the levels have to hold for the whole rated duration. So a reading taken shortly after the supply goes off shows what the lighting gave at that moment. It doesn't show what it gives near the end of the battery, when the light is at its weakest.

A lux check on its own is still worth doing. It finds dark stretches between fittings, missing or misaimed luminaires and routes that were never lit properly. Just record it for what it is, and don't let anyone read it as a duration test.

What BS 5266-1 covers

BS 5266-1 is the UK code of practice for emergency lighting of premises, published by BSI. It covers premises other than homes, apart from the common access routes in blocks of flats. HSE's guidance on lighting at work, HSG38, sends readers to it for the light levels escape lighting needs.

For lux levels, the code treats areas by what they're for:

• Escape routes. The corridors, passages and stairs people use to reach a final exit. The code sets a minimum level on the floor of the route.
• Open areas. Larger rooms and spaces with no defined route through them, sometimes called anti-panic areas. Here the aim is enough light for people to find their way to an escape route, and the code sets a minimum across the floor, leaving out a border at the walls.
• High-risk task areas. Places where someone is doing something dangerous when the power fails, and needs to see well enough to make it safe before leaving. These have their own level, separate from the escape routes.

HSG38 also names places that need particular attention when lighting is planned: emergency exits, escape routes, escalators, plant rooms, direction signs, fire alarm points and fire-fighting equipment.

The figures and the conditions attached to them are in the code, and we don't reproduce them here. Buy the current edition from BSI, or use a copy your employer or professional body gives you access to. If a client's specification or your fire risk assessment names a figure, that's the one the check is measured against, and it may ask for more than the code.

BS 5266-1 is a code of practice. It gives guidance, not a pass mark. Readings show how the lighting measured against a figure. Whether the emergency lighting is adequate is a judgement for a competent person and for whoever is responsible for fire safety in the building.

What the law asks for

In England and Wales, the Regulatory Reform (Fire Safety) Order 2005 requires emergency routes and exits that need lighting to have emergency lighting of adequate intensity if their normal lighting fails. Scotland has its own fire safety law, under the Fire (Scotland) Act 2005. The Workplace (Health, Safety and Welfare) Regulations 1992 also require suitable and sufficient emergency lighting in any room where people at work would be in particular danger if the artificial lighting failed.

None of these gives a lux figure, and none names a lux check. The figures come from the code of practice, and a lux check is how you find out what the installation actually delivers.

How to check emergency lighting levels with a lux meter

The method in the order you do it.

1. Know what you're measuring against. Get the figure from your copy of BS 5266-1, the fire risk assessment or the client's specification, and find out which spaces are escape routes, open areas and high-risk task areas. The emergency lighting design drawings usually show this, if they exist.
2. Plan it with the person responsible for the building. Turning off the normal supply leaves the building on its emergency lighting, so do it when the space is empty of its normal users and people know it's happening. After a discharge, the batteries take time to recharge, and the building has less emergency cover until they have.
3. Check the meter. Note its make, model, serial number and calibration certificate, and check it reads reliably at very low levels. See the meter you need below.
4. Get the space dark. Daylight, street lighting and light spilling in from areas that are still lit all add to the reading. At emergency levels, a little stray light makes a big difference. Measure after dark or with the daylight kept out, and note any stray light you couldn't remove.
5. Switch off the normal supply. Simulate a failure of the normal lighting supply, usually with the test key switch or by isolating the lighting circuits, so the emergency luminaires switch over as they would in a real failure. Note the time, and let them settle at full output before the first reading.
6. Lay out the points. On an escape route, readings go along the centre line of the route, closer together on a shorter route, with a strip along each side left out. In an open area, they go on an even grid across the floor, leaving out a border at the walls, and every point is measured. On escape stairs, they go on the front edge of the treads. The darkest spot is usually midway between two luminaires, so make sure the layout catches it.
7. Take the readings. Sensor flat on the floor and facing up, with you standing clear so your body doesn't shade it. Record each reading with where and when it was taken.
8. Restore the supply. Note the time, and check that every luminaire is back on charge.
9. Work out the results. The lowest reading on each route and area, and on escape routes, how the brightest compares with the darkest along the centre line. Compare each with the figure you're measuring against, and say what you compared.

The meter you need

Emergency levels are a small fraction of normal working light, which is where many lux meters are least accurate. Before you rely on one, look at what its maker states for accuracy, and how that holds at the bottom of its range.

Take the Chauvin Arnoux C.A 1110 as an example. Its maker states an accuracy of 3% of the reading, plus or minus 2 display points, and it reads in steps of 0.1 lux on its lowest range. Those 2 display points are a fixed amount, so in very low light they're a large share of the reading.

Best practice for emergency measurement also asks more of the meter than an ordinary survey does. Check what instrument your client's specification asks for before you start.

A phone's light sensor is not a calibrated instrument, and phone lux meter apps aren't built for light this low. Are lux meter apps accurate enough?

What to record

Someone who wasn't there should be able to check the result from the record alone. At the least, record:

• the site, each area, and whether it's an escape route, open area, stairs or high-risk task area
• the figure you measured against, and where it came from
• the meter, its serial number and its calibration certificate
• the conditions: how dark it was, any stray light, and whether the space was empty
• when the normal supply went off and came back, and when each reading was taken
• whether a duration test was running, and if not, that this was a level check only
• every reading, with where it was taken
• the lowest and highest readings for each route and area
• any luminaire that didn't light, any point you couldn't measure, and why
• who took the readings, and when

For the general report checklist, see what a lighting survey report should contain.

How Luxwork records an emergency lighting check

Luxwork is a lighting survey app for iPhone and iPad. It doesn't measure light itself. It takes each reading from your meter, over Bluetooth or typed from the display, and puts it on the plan where you took it. Emergency lighting levels are part of the same app as normal surveys, not an add-on.

• Emergency is chosen at the start. Before the first reading, you say whether you're measuring the normal lighting or the emergency lighting. An emergency survey stays an emergency survey, and its readings are never mixed with normal ones.
• The points follow the area. Choose escape route, open area or stairs, and Luxwork lays out the points the best-practice way for it: the centre line of a route, a grid over an open area, or the front edge of the treads. If you set your own spacing instead, the report says so.
• Every reading is traced. Each one carries the meter it came from, that meter's calibration record, its position on the plan and the time it was taken.
• The report says what kind of check it was. It calls the survey a level check, records the levels the emergency luminaires were giving at the time, and states that it shows nothing about how long they hold their output. If you entered a figure, the report prints it with the measured levels beside it and marks it not assessed, because the figure has to hold to the end of the rated duration, and a level check can't show that.

Signed on the device. Any change to the signed survey record breaks the signature check.

Questions people ask

What lux level is required for emergency lighting?

The figures for escape routes, open areas and high-risk task areas are in BS 5266-1, each with conditions attached. We don't reproduce them. Use your own copy of the code, or the figure your fire risk assessment or client names, which may be higher.

Where do I find the BS 5266 lux levels?

In BS 5266-1 itself, from BSI or through a subscription your employer or professional body may hold. Make sure you have the current edition. Summaries online sometimes mix up figures from different documents, so check any figure you use against the code.

Is a lux check the same as the emergency lighting duration test?

No. The duration test runs the system on battery for its full rated duration to show the batteries last. A lux check measures how much light the luminaires give. A reading taken soon after switchover shows the light at that moment, not the light at the end of the battery.

Can I check emergency lighting with my phone?

Not in a way anyone else can rely on. A phone's light sensor is not a calibrated instrument, and emergency levels are very low, so any error in a reading is a larger share of it.

Does the check have to be done in the dark?

Yes, or as near to it as you can get. Any daylight or light from elsewhere adds to the reading, and at emergency levels even a little of it can hide a dark stretch. Record any stray light you couldn't remove.

How often should emergency lighting levels be checked?

No law in Great Britain sets an interval for measuring them. BS 5266-1 and the testing standards it works with set out routine tests and when the levels should be checked, so check your copy, the fire risk assessment and any contract. Check again after alterations, new fittings or a change in how the space is used.

Does a lux check show the emergency lighting is good enough?

Not on its own. It records what was measured and how it compared with the figure you chose. It says nothing about how long the batteries last. Whether the installation is adequate is a judgement for a competent person and for whoever is responsible for fire safety in the building.

Who can carry out an emergency lighting lux check?

Someone competent in emergency lighting, usually an electrical contractor, an emergency lighting specialist or a lighting engineer. They need to know the method, use a calibrated meter that reads low light reliably, and record enough for a reader to check the work.