Retrofit & economics

The emergency circuit you inherited: what a lamp swap does to a life safety system

Why a maintained fitting that still illuminates is not evidence the emergency system survived a retrofit, the four things a T8 conversion changes on an emergency circuit, what the duration test proves and what it does not, and the record that has to exist before the building is handed back.

Written by Yilian Zhikong Technology (Shenzhen) Co., Ltd. · Last reviewed August 2026

Emergency lighting is the part of a retrofit where the consequence of getting it wrong is not a complaint. It is also the part most likely to be treated as out of scope, because the emergency fittings look separate, the certificates are in a folder somebody else keeps, and the brief said "replace the lighting". On a great many refurbishments the emergency system is quietly modified by people who did not know they were modifying it.

Maintained, non-maintained, and the thing that looks fine

A maintained emergency luminaire is lit in normal operation and stays lit on loss of supply. A non-maintained one is dark until the supply fails. In a refurbishment, the maintained fittings are the dangerous case, because a maintained fitting whose emergency function has been destroyed looks exactly like a maintained fitting that works. It is on. It is bright. It is part of the general lighting scheme, and nobody notices anything until the annual duration test, or until it matters.

That is the whole reason emergency lighting has a mandated testing regime rather than an inspection: the failure is invisible by design.

Four things a conversion changes

Take the commonest case — linear fluorescent converted to LED tubes, covered generally in T8 fluorescent to LED. On a fitting with an emergency battery pack, each of these is a live issue:

1. The inverter's compatibility with the new load. An emergency pack was designed to drive a specific lamp technology at a specific power in the emergency condition. Presented with an LED tube it may drive it at the wrong level, may not strike it at all, or may operate outside its own design envelope. "It lit up on test" is not the same as "it will deliver the rated output for the rated duration".
2. The emergency light output. EN 1838 specifies illuminance on escape routes, in open areas and at high-risk task locations, and the emergency output of a converted fitting is very often lower than the original — the pack drives a fraction of full power, and that fraction of a different lamp is a different number of lumens distributed differently. The compliance question is photometric, and it needs a calculation, not a glance.
3. The distribution. A fluorescent tube emits in all directions; many LED replacements emit into a limited beam angle. On an escape route the relevant quantity is illuminance along the centre line with a uniformity requirement, and a narrower distribution changes both while leaving the total lumens looking similar.
4. The certification of the assembly. The emergency luminaire was certified as a product. Substituting the light source inside it makes the installer responsible for the modified assembly, in the same way and for the same reason as a ballast bypass does.

What the duration test proves

The regime in EN 50172 and BS 5266-1 requires a short functional test at monthly intervals and a full-duration discharge annually, with records. The annual test proves that on that day, the battery sustained the fitting for the rated duration. It does not prove that the light produced during that duration meets the photometric requirement, and in a converted fitting those are exactly the two things that have come apart.

So on a retrofit, the acceptance evidence has to include both: the duration test, and a photometric verification of the emergency condition — either a calculation using the emergency-mode photometry of the modified fitting, or measured illuminance on the escape route with the supply removed. The second is straightforward to do at handover, takes an evening, and is far cheaper than the first argument about it.

The four decisions worth taking early

1. Convert, or replace the emergency fittings outright? Dedicated emergency luminaires are inexpensive relative to the risk, and replacing them removes the entire compatibility question. On most projects this is the right answer and it is usually rejected on cost before anyone has priced the verification work the alternative requires.
2. Central battery or self-contained? If the building has a central system, the retrofit interacts with it differently and the load calculation on the central inverter has to be revisited — the new load is not the old load.
3. Does the escape route layout still hold? Refurbishments move partitions. The emergency scheme was designed against a floor plan, and a new plan needs a new design regardless of what happened to the fittings.
4. Who is the responsible person? Someone has to sign the completion certificate for the modified system and hold the log book afterwards. Establish who before the work starts, because that person will have questions the programme needs to accommodate.

The handover record

A retrofitted emergency system that cannot be evidenced is a liability, and the evidence is documentary. What has to exist when the building is handed back:

• A drawing of the emergency scheme as installed, against the current floor plan, with fitting types and locations.
• Photometric verification of the emergency condition — calculation or site measurement — against EN 1838 for each escape route, open area and high-risk task location.
• The declaration for the modified assembly where fittings were converted rather than replaced, naming who takes responsibility for it.
• Completion certificates, the log book, and the test schedule handed to a named person with the date of the first due test written in it.
• Spares, and where they are. A system whose replacement parts were discontinued between design and first failure is a system that will be repaired with something else.

None of this is unusual or onerous; all of it is routinely absent. The general requirements it derives from are set out in emergency lighting basics, and the fire safety legislation of your jurisdiction takes precedence over every sentence here.