Photoluminescent exit signs store light and glow after a power failure without any energy source of their own, but they fade steadily; illuminated exit signs are lit at constant luminance for the full rated duration by an exit sign luminaire with a battery or central battery supply. Where emergency escape lighting is required, exit signs generally have to be electrically illuminated. Photoluminescent signs are common where no escape lighting is required, or as a supplement, for example in low-level wayfinding systems.
What is a photoluminescent exit sign?
A photoluminescent exit sign is a sign containing pigments that absorb light and release it as an afterglow when the lighting fails. It needs no mains connection and no battery. On a typical sign the green area is printed while the light areas glow.
Performance is measured and classified under national standards – in Germany, for example, DIN 67510, which describes how the afterglow luminance is determined at defined times after the excitation is switched off. Manufacturers state the resulting class on the product or data sheet.
Two properties matter for planning:
- Charging: the sign only glows if it has previously been lit long and brightly enough. In dark areas, or where the general lighting is switched off, it does not charge. The type of light source can also matter; follow the manufacturer's data on the required excitation.
- Decay: luminance is highest just after the lighting fails and then falls continuously. A photoluminescent sign cannot deliver constant luminance over one or three hours.
What is an illuminated exit sign?
With an illuminated exit sign, an electrical light source keeps the sign legible during a power failure. There are two variants:
- Internally illuminated: the pictogram is part of an exit sign luminaire and lit from within.
- Externally illuminated: a printed sign is lit by a nearby emergency luminaire.
Power in emergency mode comes either from a battery inside the luminaire (self-contained system) or from a central battery system. Throughout the rated duration the sign must meet EN 1838 – for example at least 2 cd/m² luminance on the green area and a white-to-green contrast between 5 : 1 and 15 : 1. The minimum rated duration is 1 hour; many buildings require 3 hours, see Emergency lighting duration.
When are photoluminescent signs sufficient?
Across Europe, escape routes and emergency exits must be signed with ISO 7010 signs, but whether they must be electrically lit depends on national rules. In Germany, for instance, workplace rule ASR A2.3 requires escape routes to be signed and ASR A1.3 governs sign design. Where no emergency escape lighting is required – such as smaller workplaces with short, clear escape routes – non-illuminated signs are often sufficient. To keep them legible when the general lighting fails, they are usually photoluminescent.
Typical uses:
- workplaces without an escape lighting requirement, where the risk assessment allows it,
- supplementing existing escape lighting, for example on stair nosings, handrails or door frames,
- low-level wayfinding systems that remain visible below a smoke layer,
- photoluminescent versions of fire equipment signs and evacuation plans.
A precondition is always that the general lighting charges the signs adequately in normal operation.
When must exit signs be illuminated?
The rule of thumb: where emergency escape lighting is required, exit signs must also be electrically illuminated during a power failure. In those locations photoluminescent signs generally supplement rather than replace illuminated signs.
Escape lighting is typically required in:
- places of assembly, shops, hotels, hospitals, care homes, schools and high-rise buildings,
- workplaces where the risk assessment calls for it, for example because of size, many people unfamiliar with the building or high-risk task areas,
- buildings where the building permit or fire strategy specifies it.
In many such buildings exit sign luminaires are operated in maintained mode, staying lit even when mains power is available. Requirements by country are summarised in Emergency lighting requirements.
Important: The deciding documents are always the building permit, fire strategy, national regulations and, in workplaces, the risk assessment. A decision that photoluminescent signs are sufficient should be documented there.
How far can the signs be seen?
For electrically illuminated signs, EN 1838 sets the formula d = z × h: viewing distance equals distance factor times pictogram height, with z = 200 for internally illuminated and z = 100 for externally illuminated signs.
| Pictogram height h | Externally lit (z = 100) | Internally lit (z = 200) |
|---|---|---|
| 10 cm | 10 m | 20 m |
| 15 cm | 15 m | 30 m |
| 20 cm | 20 m | 40 m |
Photoluminescent signs are not covered by this EN 1838 distance factor; national rules such as ASR A1.3 in Germany give separate sizing guidance for non-illuminated signs. In practice a photoluminescent sign of the same size is legible over a noticeably shorter distance than an internally illuminated one, and its legibility declines over time after the power failure. Long corridors and large halls therefore need larger signs or shorter spacing. The calculation for illuminated signs is in Exit sign viewing distance.
Comparison table: photoluminescent vs illuminated
| Criterion | Photoluminescent | Illuminated (internally lit) |
|---|---|---|
| Energy source | stored ambient light | battery in luminaire or central battery |
| Luminance in an emergency | highest at first, then fades | constant over the rated duration |
| Measurement standard | national, e.g. DIN 67510 | EN 1838, EN 60598-2-22 |
| Viewing distance | shorter, depends on size and time | d = 200 × h, e.g. 30 m at 15 cm |
| Precondition | adequate general lighting for charging | mains connection |
| Meets an escape lighting requirement | generally no | yes |
| Testing | visual check, cleanliness, charging | monthly function test, annual duration test |
| Wear parts | none electrical; ageing and dirt | battery, at least 5 years life for LiFePO4 |
| After alterations | new sign | swap pictogram film, depending on luminaire |
What about purchase and maintenance costs?
Photoluminescent signs are inexpensive to buy and need no electrical installation. Running costs are minimal, but there is effort for regular visual checks, cleaning and replacing damaged or faded signs. A hidden factor is the general lighting: areas that stay dark at night or at weekends do not charge the signs.
Exit sign luminaires cost more because of the luminaire, installation and wiring. Testing under EN 50172 – monthly function tests and annual duration tests – and battery replacement come on top. With self-testing luminaires these tests run automatically; the NOTLUX exit sign luminaire of the Series 19 tests itself, logs results via Bluetooth and app, and has a replaceable LiFePO4 battery with a service life of at least 5 years. An overview of cost drivers is in Emergency lighting costs.
To find out which solution your building requires, we start with an on-site survey – get in touch via contact.
Frequently asked questions
Are photoluminescent exit signs enough?
Where no emergency escape lighting is required, photoluminescent signs are a common solution. Where escape lighting is mandatory, they generally supplement illuminated exit signs rather than replace them.
How long do photoluminescent exit signs glow?
Luminance is highest immediately after the lighting fails and then falls continuously. How bright a sign still is after a given time depends on the pigment, the charging and the product class, measured for example under DIN 67510.
Do photoluminescent signs need testing?
There is no electrical test, but regular visual checks are advisable: are the signs present, clean, undamaged and adequately lit? Faded or dirty signs should be replaced.
Can I replace exit sign luminaires with photoluminescent signs?
Only where no escape lighting is required and the building permit, fire strategy and risk assessment allow it. In buildings with mandatory escape lighting this is generally not acceptable.
Why are illuminated exit signs legible from further away?
They are lit at a constant, defined luminance and high contrast. EN 1838 therefore allows a distance factor of z = 200 for internally illuminated signs, twice that of externally lit signs.
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