TECHNOLOGY — MATERIALS
The material that determines the luminaire’s service life.
A street luminaire is exposed to UV, moisture, salt, temperature cycling and mechanical stress for decades. That is why the housing is a technical part of the system’s service life — not merely a styling detail. Here we explain how material choice affects operational reliability, maintenance requirements and system integration.
ORIGINS
The same material family that kept Bakelite alive for over a hundred years.
SMC is not a new material — it has a long industrial track record. It is the next step in a lineage that begins with Bakelite in 1907 — the world’s first fully synthetic thermoset plastic — which was reinforced with glass fibre during the 1930s to create what is known as FRP, fibre-reinforced polymer. The modern polyester-based SMC process was developed in West Germany in the early 1960s and first established itself in electrical and telecom applications across Europe and Japan, before achieving its major breakthrough in the United States.
That is why SMC is still used where material choice determines operational reliability: switchgear enclosures, signal housings, third-rail insulators and network infrastructure. VALDUR builds on the same logic — electrical safety and design freedom, but with considerably better mechanical performance and weather resistance than early thermosets.
FOUR CONSTITUENTS
What SMC actually consists of.
STRUCTURAL REINFORCEMENT
Glass fibre
Provides stiffness, strength and dimensional stability — what elevates SMC far above unreinforced plastics.
MATRIX
Thermoset resin (polyester)
The cured, cross-linked network that binds the fibres together and cannot be remelted.
FILLERS
Mineral fillers
Adjust dimensional stability, shrinkage, stiffness and fire properties.
ADDITIVES
Process and protective additives
UV stabilisers, low-shrink agents and thickeners that control how the sheet matures before moulding.
Material data varies between SMC formulations and suppliers. Values on this page refer to typical industrial/electrical SMC grades — not a single universal SMC value.
THE PROBLEM WITH METAL
Galvanic corrosion begins at the interface.
Aluminium housings exposed to road salt, sea air or industrial pollutants corrode over time — the process is further accelerated by contact between dissimilar metals (galvanic corrosion), for example where screws, brackets or contacts made of another metal meet the housing.
A composite housing has no metal surface that can oxidise. There is simply no galvanic cell to form — which eliminates electrochemical corrosion in the luminaire housing itself rather than merely delaying it.
Where metal fixings are still required — for mounting and load-bearing construction — POLAB uses marine-grade stainless steel (316), which itself resists salt corrosion far better than standard fixings.
At Smögen Pier in Sotenäs, VALDUR luminaires have been in continuous coastal service since 2024 — now the largest single VALDUR installation to date and the primary field reference for long-term performance in a high-salinity marine environment. For a deeper look at the electrochemistry behind corrosion in luminaire housings, see Why Luminaire Housings Corrode in the knowledge base.
INGRESS & IMPACT PROTECTION
Protected against weather, water and mechanical impact.
IP66
Dust-tight and protected against powerful water jets
The rating means complete protection against dust ingress and protection against powerful water jets from all directions — relevant in both heavy rain, hosing down and external cleaning.
IK08
Mechanically impact-resistant housing
The IK rating indicates the housing’s resistance to mechanical impact, which is relevant during installation, transport and in environments with risk of external impact, e.g. from gravel or ice.
MANUFACTURING
400 tonnes of compression — not die-casting.
SMC composite is manufactured by compression moulding under very high pressure, rather than being cast like aluminium. The result is a denser material with more consistent properties throughout the housing — and a luminaire housing that is both lighter and longer-lived than its metal counterpart. Compression moulding at 150°C under controlled pressure eliminates the porosity and surface imperfections associated with die-casting.
400 t
Clamping force during moulding
~33 %
Lower density than aluminium
1.8 kg
Housing body weight
30+ yrs
Expected material service life
THE PROCESS IN THREE STEPS
From sheet to finished housing.
STEP 1
Sheet layering
Resin paste is applied to a carrier film, chopped glass fibre is dispersed on top, and a second film layer forms a sandwich that is rolled so the fibres are wetted out and the material homogenised.
STEP 2
Maturation
Over several days viscosity increases as the thickening system reacts — an often overlooked but critical step to make the sheet mouldable without the fibres washing away in the tool.
STEP 3
Moulding
The matured sheet is cut, placed in a heated steel tool and cured under high pressure — the industry benchmark is around 1,000 tonnes per square metre of moulded area.
VALDUR’s housing is moulded at 150 °C with 400 tonnes of clamping force — in line with industry benchmarks for a moulded area of this size.
THE THERMAL TRADE-OFF
SMC insulates against heat. That is why we solve the LED module’s own heat differently.
SMC composite’s low thermal conductivity (approximately 0.7 W/mK, versus aluminium’s 130–160 W/mK) is an advantage when the task is to keep summer sun and ambient heat out of the electronics. But that same property makes SMC unsuitable as a heat sink for the heat the LED module itself generates during operation.
VALDUR therefore uses a hybrid approach rather than expecting a single material to do everything: SMC carries structure, insulation and weather resistance, whilst dedicated internal aluminium heat sinks conduct heat away from the LED module. This patent-pending thermal management technology, developed by POLAB, contributes to a lower operating temperature and a long service life for both the electronics and the driver. Operating temperature range: −40°C to +35°C ambient; dimensional stability maintained across thermal cycling from −40°C to +80°C.
THE PATH HEAT TAKES
LED module
Generates heat during operation
Internal aluminium heat sinks
Conducts heat away from the LED module
SMC housing (exterior)
Keeps out solar and ambient heat
ADDITIONAL MATERIAL PROPERTIES
Electrically insulating, radio-transparent — and a lighter footprint for the climate.
ELECTRICAL SAFETY
Naturally electrically insulating
Unlike a metal housing, SMC composite does not conduct electricity, eliminating the risk that an internal insulation fault causes the entire luminaire housing to become live.
RADIO TRANSPARENCY
Wireless signal without apertures in the housing
The housing passes radio signals through, making it possible to integrate antennas for wireless control systems directly inside the luminaire — without external antennas or cable glands that would otherwise compromise the housing’s ingress protection. The same principle is used in composite radomes for 5G masts and satellite communications, where the housing must protect electronics without attenuating the signal.
ENVIRONMENTAL FOOTPRINT
Lower energy demand during manufacturing
Aluminium production requires energy-intensive smelting and electrolysis, plus usually a separate surface treatment for corrosion protection that SMC composite manages without. Conversely, aluminium is easier to recycle at scale — established aluminium recycling requires only a fraction of primary energy, with no quality loss. An honest trade-off: SMC has the advantage in manufacturing and maintenance-free operation; aluminium has the advantage at end-of-life recycling.
AGEING IN PRACTICE
Cosmetic yellowing, not structural collapse.
Like all polymers, SMC is affected by UV, moisture and temperature over time — it would be dishonest to claim otherwise. Research on glass fibre reinforced composites shows that moisture and UV can affect strength and stiffness, through plasticisation and surface oxidation.
In practice this effect is confined almost exclusively to a thin, resin-rich surface layer of 50–100 μm. The consequence is typically cosmetic — slight yellowing or minor surface wear — rather than a weakening of the housing’s load-bearing function.
This is not an assumption: SMC/GRP cable enclosures in continuous outdoor service since the early 1960s are still in use with European network operators, and several manufacturers of SMC enclosures in outdoor service for electricity networks cite documented service lives of over 40 years. UV resistance and colour stability are maintained over service life due to the material’s inherent composition.
WHAT ACTUALLY HAPPENS OVER TIME
Surface layer (0–100 μm): slight yellowing and microscopic surface wear from UV exposure.
Load-bearing structure: the glass fibre reinforcement lies hidden beneath the surface layer and is marginally affected by normal outdoor exposure.
Function: electrical insulation, ingress protection and mechanical strength remain even when the surface has begun to age visibly.
COMPARISON
How SMC compares to other housing materials
Material properties in outdoor service — the factors affecting service life, maintenance requirements and system integration.
| Property | SMC Composite | Aluminium | Steel |
|---|---|---|---|
| When the surface is scratched | Same material all the way through Colour-through. No protective surface to damage. |
Dependent on surface treatment integrity Painted: surface layer is decisive. Anodised: integrated oxide layer, but sensitive at edges and damage zones. |
Surface protection can be breached Corrosion protection resides in the surface layer. |
| Galvanic corrosion | No galvanic corrosion in the material Non-metallic housing. |
Risk at contact with dissimilar metals Accelerated by chloride and moisture. |
Corrosion risk without protective system Requires active surface treatment. |
| Surface treatment for corrosion protection | No paint system required Colour-through material. No paint, no powder coat, no anodising required. |
Painting or anodising Periodic renewal. |
Painting or galvanising Periodic renewal. |
| Wireless communication | Antenna can be integrated in the luminaire SMC does not affect the radio signal. |
Metal limits radio signal Requires external antenna or cable gland. |
Metal limits radio signal Requires external antenna or cable gland. |
| Electrical insulation | Non-conductive material Eliminates risk of live housing. |
Electrical conductor Requires separate earth connection. |
Electrical conductor Requires separate earth connection. |
| UV resistance | UV-stable by construction Surface zone may yellow; housing is not structurally affected. |
Depends on surface treatment Paint systems and anodising have varying resistance. |
Depends on surface treatment UV resistance of the paint system is decisive. |
| Weight (density) | ~1.8 g/cm³ Lightweight. |
~2.7 g/cm³ (+50 %) Lightest of the metals. |
~7.8 g/cm³ (+330 %) Heavy. |
| Thermal conductivity | ~0.7 W/mK (thermal insulator) Separate cooling solution for LED module. See note below. |
130–160 W/mK Suitable as integrated heat sink. |
~50 W/mK Good thermal conductivity. |
| Recyclability | Mechanical recycling possible Thermoset cannot be remelted. |
Remelting possible Established recycling process. |
Remelting possible Established recycling process. |
| Maintenance in coastal environments | No paint system to renew Corrosion protection is a property of the material, not the surface treatment. |
Periodic upkeep Surface layers age faster in saline environments. |
Requires active maintenance Corrosion escalates without maintenance. |
On thermal conductivity and LED cooling
SMC’s low thermal conductivity is an advantage when keeping ambient heat out of the electronics. For the heat the LED module itself generates, SMC requires a separate thermal path — in VALDUR this is achieved with internal aluminium heat sinks. See The Thermal Trade-off above for a detailed description.
Density and thermal conductivity values are typical for each material class. SMC values refer to typical electrical/infrastructure SMC grades (e.g. Menzolit SMC 0200).
WHY THIS MATERIAL FOR STREET LIGHTING?
Composite materials in demanding infrastructure.
The examples below show how fibre-reinforced polymers (GRP, FRP, SMC, BMC) are used in environments where corrosion, electrical insulation, low weight or radio transparency place high demands on the material. Common to all applications is that the material family was chosen based on performance, not convention. See note below for material-specific information.
TECHNICAL ENCLOSURES
Electricity networks and secondary substations
GRP-encased secondary substations and cable housings for electricity networks are used in long-lived outdoor installations by European network operators. The material is chosen where long-term operational reliability is prioritised.
RAIL
Third-rail insulators
SMC insulators for third rails are used in metro and light rail systems internationally, with specified requirements for electrical insulation, impact resistance and UV stability.
COMMUNICATIONS
Radomes for 5G and satellite
Composite radomes protect antennas against weather without attenuating the signal — requiring the combination of low dielectric loss and mechanical strength in the same material.
MARINE ENVIRONMENTS
DNV-classified products
Composite gratings and profiles are approved for installation on DNV-classified vessels, chosen for corrosion resistance in saltwater environments.
INDUSTRIAL COMPONENTS
Automotive and domestic appliances
SMC and BMC are used in bonnets, electrical boxes and white goods in series production — processes requiring precise tolerances and repeatable quality.
RAIL INFRASTRUCTURE
Eurobalise housing (Alstom)
Alstom’s Eurobalise signalling unit has been manufactured in glass fibre composite since 2014 in batches of 15,000–25,000 units per year, with requirements for mechanical and climatic performance.
Third-rail insulators and a number of electricity network solutions are explicitly SMC. Other examples refer to GRP, FRP or BMC — closely related variants within the same material family.
MATERIAL PROPERTIES
The material’s service life is not the electronics’ service life.
A luminaire is a system with components that age at different rates and for different reasons. The housing, LED module, driver and optics have distinct failure mechanisms — and the material choice for the housing affects how long the other components can be replaced.
Luminaire housing (SMC)
Degrades primarily through UV exposure in the surface layer and mechanical loading. The load-bearing structure is marginally affected by normal outdoor exposure. See the Ageing in Practice section above for how effects actually distribute.
LED module
Lumen depreciation is the primary ageing mechanism. High operating temperatures accelerate degradation — which is why the housing’s thermal insulating ability indirectly affects the LED module’s service life.
Driver
Electrolytic capacitors are typically the most sensitive component. The ageing rate approximately doubles per 10 °C temperature increase. The driver is designed as a replaceable component in VALDUR.
THE CONSEQUENCE FOR MATERIAL CHOICE
If the housing corrodes or cracks first — regardless of whether the electronics are functional — the luminaire must be replaced. The housing sets a floor for the entire system’s service life.
If the housing survives, the electronics can be upgraded separately. LED modules and drivers are replaceable in VALDUR without replacing the housing.
The SMC housing’s thermal insulating ability reduces temperature variation inside the luminaire, which benefits capacitors and electronics positively during long operation.
KEY DATA
Materials & housing — summary
| Parameter | Value |
|---|---|
| Housing material | SMC composite (Sheet Moulding Compound) — glass fibre reinforced polymer composite |
| Manufacturing method | Compression moulding, 400 t clamping force, 150°C |
| Housing body weight | 1.8 kg |
| LED module thermal management | Internal aluminium heat sinks (patent-pending technology) |
| Expected material service life (typical) | 30+ years |
| Corrosion resistance | SMC composite does not corrode electrochemically — no galvanic cell, no pitting pathway. Designed for coastal, marine, and industrial environments. |
| Ingress protection | IP66 |
| Impact resistance | IK08 |
| Operating temperature | −40°C to +35°C |
| Galvanic corrosion risk | None (no metal on housing exterior) |
| Electrical insulation | Yes, non-conductive housing |
| UV impact | Cosmetic surface yellowing possible over time; load-bearing function unaffected |
| Fixings | Marine-grade stainless steel 316 |
STANDARDS
Relevant standards for materials & housing
ISO 12944
Classification of corrosivity environments, C1–C5-M.
ISO 9227
Salt spray test for evaluation of corrosion resistance.
IEC 60598-1
General safety requirements for luminaires.
IEC 62262
Classification of mechanical impact protection (IK codes).
FREQUENTLY ASKED QUESTIONS
About materials & corrosion protection
Why does POLAB use composite instead of aluminium?
Aluminium corrodes over time in coastal and road-salt environments, particularly at galvanic contact with other metals. SMC composite has no metal surface that can oxidise, which eliminates galvanic corrosion entirely rather than merely delaying it.
Is VALDUR rated to the C5-M corrosion class?
C5-M (per ISO 12944) classifies atmospheric corrosivity environments and the performance of protective coating systems on metallic substrates. SMC composite — the material used in VALDUR’s housing — does not undergo electrochemical corrosion and does not rely on a paint or coating system. C5-M certification, as defined for metallic systems, is therefore not directly applicable to SMC composite’s inherent corrosion properties. VALDUR is designed for the environments that C5-M describes: coastal, marine, and industrial locations with high salt and moisture loading.
Can SMC composite withstand the same mechanical stresses as metal?
VALDUR’s housing is IK08-rated, meaning documented resistance to mechanical impact per IEC 62262. The surface may yellow slightly from UV over many years, but that is a cosmetic effect — the load-bearing function is not affected.
Does the composite housing need repainting or maintenance?
Because the material does not corrode or rust, no periodic repainting is required for corrosion protection, which reduces the long-term maintenance cost compared with metal luminaires.
If SMC insulates against heat, how is the LED module cooled?
Via internal aluminium heat sinks that conduct heat away from the LED module. The SMC housing’s role is to protect and insulate from the outside — not to act as a heat sink. Read more under The Thermal Trade-off above.
READ FURTHER
Related technologies
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