Explosion-proof luminaires are usually specified last and inspected first. The lighting design decides the wattage, but the area classification decides whether that luminaire is allowed in the building at all — and the two are often done by different people.
This is the order that avoids rework: marking first, light level second, then beam, power, materials and finally maintenance access.
Step 1: fix the marking before anything else
Nothing downstream matters if the enclosure is not permitted in the area. Take the marking straight from the area classification:
| Your zone | Minimum EPL | Typical luminaire marking |
|---|---|---|
| Zone 1, gas group IIC | Gb | Ex db IIC T6 Gb |
| Zone 1, gas group IIB | Gb | Ex db IIB T6 Gb |
| Zone 2 | Gc | Ex n or Ex db, depending on the project |
| Zone 21, conductive dust | Db | Ex tb IIIC T80°C Db |
| Gas and dust together | Gb / Db | Ex db IIC T6 Gb; Ex tb IIIC T80°C Db |
Two details from the classification go straight onto the enquiry and are frequently omitted: the temperature class and the ambient range. If your site reaches +50 °C, a luminaire certified only to +40 °C does not cover the installation, regardless of its marking. Background on both is in hazardous area classification and reading an Ex marking.
Step 2: decide the light level before the wattage
Buyers often start from “we had 150 W before”, which bakes in the old technology’s efficiency. Start from the illuminance the task needs instead, then size the luminaire to deliver it.
| Area | Typical maintained illuminance |
|---|---|
| Piping and tank areas, general plant | 50 lux |
| Walkways, platforms, stairways | 20 – 30 lux |
| Loading bays and transfer areas | 100 lux |
| Operating areas around machinery | 150 – 200 lux |
| Inspection and maintenance points | 200 lux |
| Control rooms and workshops | 300 – 500 lux |
These are project-level targets typical of industrial practice rather than a substitute for a lighting design. What matters here is the method: lux target → lumens required → luminaire wattage and count, with a maintenance factor for dirt and lumen depreciation of typically 0.7 to 0.8 in a process environment.
Sizing on old wattages overshoots badly with LEDs. A modern LED luminaire delivers roughly 100 to 150 lumens per watt, where a fluorescent installation of comparable light output often worked at 60 to 90 lumens per watt including control gear losses. A straight watt-for-watt replacement usually over-lights the area and wastes the saving.
Step 3: match the beam to the mounting height
The same luminaire at two mounting heights can produce either a bright pool or unusable glare.
- Above 8 m. Use a narrow to medium beam with a controlled distribution, otherwise most of the light lands between the fittings.
- 4 to 8 m. Medium distribution covers most walkway and general plant applications.
- Below 4 m, or where people work under the fitting. Wider distribution, lower glare, and attention to the diffuser. Wall and bracket mounting at low height needs the widest option.
Mounting height also drives access. A luminaire at 12 m on a pipe rack needs a maintenance plan that does not involve scaffolding every time a driver fails.
Step 4: choose the housing for the environment, not just the zone
Ex certification says nothing about how a luminaire survives your atmosphere. That is a separate decision, and getting it wrong produces failures that have nothing to do with ignition protection.
| Condition | What to specify |
|---|---|
| Coastal, offshore, salt spray | Stainless steel 316L housing or a marine-grade coating on die-cast aluminium |
| Acid or alkali vapour | Corrosion-resistant housing, appropriate lens material, verify gasket compatibility |
| Wash-down and hose cleaning | Higher ingress protection, and check that cleaning does not exceed the rated water pressure |
| High dust loading | Design for dust layer on the housing; the surface temperature limit in the marking already accounts for it |
| High ambient, above 40 °C | Certified extended ambient range, and a check on lumen depreciation at that temperature |
Corrosion resistance is where a cheaper housing fails first: the coating breaks down at fixings and edges, water reaches the flame path joint, and the enclosure is written off long before the light source reaches its rated life. Where the atmosphere is aggressive, our BYS anti-corrosion luminaire exists for that reason.
Step 5: decide emergency lighting early
Emergency and escape lighting requirements come from local building and safety codes, and in a classified area they interact with the Ex design because the battery changes the thermal load inside the enclosure.
- Frequently the emergency version of a luminaire is a separate certification from the standard model. Check the certificate covers it.
- Typical autonomy is 90 minutes; confirm the figure your project requires rather than assuming.
- Central battery systems avoid batteries inside the classified area but need their own Ex assessment for the distribution.
Where audible warning is also required — for example at the entrance to a loading bay — a certified combined unit such as the BBJ sound and light alarm removes a second mounting point and a second cable entry.
Step 6: plan the installation and the spares
Two items get forgotten between the quotation and the commissioning:
Cable entries and glands. The thread on the luminaire must match the gland, and the gland must be certified for the same protection concept. Order them together — see the gland and conduit fitting range.
Spares and interchangeability. If a plant has eleven different luminaire types, every failure becomes a procurement exercise. Standardising on a small number of families — one floodlight, one linear, one platform light — keeps spares simple. The lighting range is organised that way: ZBD154 and ZBD140 for high mounting heights, ZBD119 for walkways and tank tops, ZBD190 for corridors and tunnels, and ZBD127 for tight spaces and local task lighting.
A worked example
A tank farm requires perimeter and walkway lighting. Four lines of information drive the answer.
- Classification: Zone 1 around the tank vents, Zone 2 for the walkways, group IIA, T3. Ambient −10 °C to +45 °C.
- Marking required: Ex db IIB T3 Gb for the Zone 1 section, with an extended ambient range covering +45 °C.
- Light level: 30 lux on walkways, 100 lux at the loading point.
- Mounting: 6 m on poles and tank structures, so a medium beam at around 150 W LED per pole, spaced to the required uniformity.
Note what did not enter the decision: the wattage of the fittings being replaced. The lux target set the luminaire, and the classification set the enclosure.
What to send with an enquiry
- Zone, gas or dust group, temperature class, ambient range
- Area to be lit, mounting height and mounting type
- Lux target or the existing lighting layout
- Supply voltage and whether dimming or emergency operation is needed
- Cable entry thread, and whether glands and distribution are also required
- Environment: coastal, chemical, wash-down, or dusty
Those six lines are enough to come back with a compliant luminaire and a realistic light level rather than a guess at the wattage.
Common questions
Can I replace a 150 W fluorescent luminaire with a 50 W LED?
Often yes, and the light level may improve. Fluorescent installations lose output with age and low temperature, while LEDs are rated differently. Check the delivered lumens rather than the wattage, and apply a maintenance factor for the environment.
Is IP65 enough for outdoor use in a classified area?
IP65 is common for outdoor hazardous-area luminaires and is sufficient against rain and hose spray from most directions. Where directed high-pressure washing or temporary flooding is expected, specify a higher rating, and confirm that the cleaning method stays within it.
Does a higher temperature class always mean a better luminaire?
No. T6 is a tighter surface temperature limit, which usually means a heavier housing or a lower power density. Specify the class the classification demands, with a margin for the substances actually present, rather than the strictest available.
Do explosion-proof luminaires need special maintenance?
Yes, and it is not difficult. The flame path and its fasteners must not be damaged or painted, gaskets must be replaced with the certified part, and the correct bolts must be refitted in the right quantity. A luminaire maintained like an ordinary light fitting loses its certification.
Send us the area, the mounting height and the lux target. We will come back with the luminaire, the marking and the layout — not a wattage guess.
