Industrial and commercial projects are decided on three numbers that are often quoted loosely: the illuminance target, the spacing that achieves it, and the payback period. These are the questions our project group answers most often when a specification moves from a tender document to a fixture schedule, with the numbers needed to check a proposal before it is accepted.
1. Illuminance and standards
Q1. What illuminance do I need for a warehouse?
It depends on the task. Circulation aisles commonly sit near 100 lux, storage and picking areas near 200 lux, and inspection or packing benches near 500 lux with a higher uniformity requirement. EN 12464-1 and the IES recommended practice documents give task-specific values, and the correct approach is to state the task rather than a single building-wide figure.
Q2. What is the difference between maintained and initial illuminance?
Initial illuminance is what the installation delivers when new. Maintained illuminance is the value at the end of the maintenance cycle, after the specified depreciation and lamp lumen depreciation factors are applied. Design to maintained illuminance, because that is the value the standard refers to.
Q3. What uniformity should I specify?
As a rule of thumb, an overall uniformity of 0.4 and a minimum to average of 0.6 are adequate for general industrial work, tighter where a task is visually demanding, and tighter again where a camera is used. State the ratio and the plane it is measured on, because a uniformity figure without a plane is not checkable.
Q4. Does glare matter in a warehouse?
Yes, particularly with high-output fixtures and low mounting heights. Unified glare rating limits apply in offices, and the same principles apply industrially where the fixture is in the field of view of a worker. A luminaire with a shielded optic and a controlled distribution reduces complaints and errors more effectively than raising the illuminance.
2. Spacing and layout
Q5. How do I calculate the fixture count?
The lumen method is adequate for a regular grid: multiply the target maintained illuminance by the floor area, then divide by the product of the fixture lumen output, the utilisation factor and the maintenance factor. Where the layout is irregular or the racking is tall, run a point-by-point simulation rather than the lumen method.
Q6. Why does the same fixture give different illuminance in two buildings?
Because the utilisation factor changes with the room surface reflectance, the room proportions and the mounting height. A dark-ceilinged warehouse with tall racking absorbs and blocks a larger share of the light, so the same fixture delivers less at the floor.
Q7. Should I mount high bay fixtures higher or lower?
Lower mounting delivers more illuminance at the floor with fewer fixtures, and it improves vertical illuminance on the rack faces, but it increases glare and requires a wider beam. Higher mounting reduces the fixture count but needs a narrower beam and more output per fixture.
Q8. What beam angle should I choose?
As a starting point, the beam angle should be roughly twice the angle subtended by the gap between fixtures at the mounting height. Too narrow a beam leaves dark bands between fixtures; too wide a beam wastes light on the walls and increases glare.
3. Ratings and environment
| Question | Short answer | Detail |
|---|---|---|
| What is the difference between IP65 and IP66? | Jet versus powerful jet | The first digit is solids, the second is water. IP65 resists water jets from a nozzle; IP66 resists more powerful jets. Both are suitable for wash-down areas, and neither implies resistance to immersion. |
| Do I need IP67 or IP68? | Only for temporary or continuous immersion | IP67 covers short-term immersion, IP68 continuous immersion at a stated depth. Most industrial interiors never need either. |
| What is IK10? | The highest standard impact rating | IK10 means the luminaire resists a 20 joule impact, which is the usual requirement for sports halls, public circulation and any area where a ball or a trolley can strike the fixture. |
| Do I need a corrosion specification? | In food, chemical and coastal sites, yes | An IP rating does not describe corrosion resistance. Ask for the housing material, the coating and the fastener grade where the ambient is aggressive. |
| What ambient temperature must the fixture tolerate? | State the maximum, not the typical | Driver lifetime is set by the ambient at the driver, which in a racked ceiling void is often far above the room temperature. |
| Are there vibration requirements? | In some industrial settings, yes | Overhead cranes, presses and transport lines impose vibration that standard terminal blocks and wire retention do not always survive. |
4. Controls and dimming
| Rating | Meaning | Typical application |
|---|---|---|
| IP20 | No water protection | Dry indoor offices and shops |
| IP44 | Protected against splashing water | General industrial interiors |
| IP54 | Dust protected and splash resistant | Workshops with dust and occasional wash-down |
| IP65 | Dust tight and jet resistant | Food production, car parks, canopies |
| IP66 | Dust tight and resistant to powerful jets | Heavy wash-down areas |
| IP67 | Short-term immersion | Occasional flooding risk |
| IP68 | Continuous immersion at a stated depth | Submerged and fountain applications |
| IK08 | 5 joule impact | General industrial |
| IK10 | 20 joule impact | Sports halls, public circulation, secure sites |
| Question | Short answer | Detail |
|---|---|---|
| Should I specify dimming? | Yes where occupancy varies | A dimmed fixture at 30 percent consumes roughly 30 percent of the power and extends the operating life, which matters most in intermittently used areas. |
| Which protocol should I choose? | DALI-2 for addressability | DALI-2 gives per-fixture addressing, dimming curves and fault reporting. A simpler 0-10 V system is cheaper but reports nothing. |
| Can I mix dimming protocols on one site? | Only with separate control zones | Different dimming curves between two protocols mean the zones will not track each other, which is visible in a shared space. |
| Do occupancy sensors actually save energy? | In intermittently used spaces, substantially | Storage aisles, stairwells and back-of-house corridors are the classic cases. In a continuously occupied production hall the saving is small. |
| Does daylight harvesting apply indoors? | In perimeter zones, yes | Rooflight-lit industrial buildings have large harvestable zones, and the sensor must be placed where it sees reflected daylight rather than direct sunlight. |
| Will dimming affect the warranty? | Usually not, within the rated range | Operating at reduced current lowers the junction temperature, which is favourable. Confirm the minimum dimming level the driver supports before writing it into the control strategy. |
5. Retrofit and economics
| Retrofit input | What to record | Why the number matters |
|---|---|---|
| Existing fixture power | Measured at the wall, including ballast loss | Nameplate lamp wattage excludes the ballast and overstates the saving if used directly. |
| New fixture power | Measured, not catalogue | Driver efficiency and dimming settings change the delivered figure. |
| Annual operating hours | From the actual schedule | The dominant variable in the payback calculation. |
| Electricity tariff | Blended rate including demand charges | A single unit rate understates the saving in buildings with demand charges. |
| Relamp and access cost | Labour plus equipment per event | In high-bay installations this often exceeds the energy saving. |
| Installed cost | Fixtures plus labour plus any wiring change | The numerator of the payback ratio. |
| Available rebate | Confirmed in writing before ordering | Rebates expire and are often contingent on a qualification listing. |
Q9. How is the payback period calculated?
Take the installed cost of the retrofit, subtract any rebate, then divide by the annual energy saving plus any maintenance saving. The annual energy saving is the power reduction in kilowatts multiplied by the operating hours and the tariff. The chart above shows how sensitive the result is to operating hours.
Q10. What maintenance saving should I include?
The avoided relamp labour and the avoided lamp and ballast replacement cost. In a high-bay installation the access cost per relamp often exceeds the lamp price, so the maintenance saving can exceed the energy saving in buildings with difficult access.
Q11. Can I keep the existing wiring?
Often yes, with attention to three points: the existing circuit voltage and phase configuration, the inrush current of the new drivers relative to the existing protective device, and the neutral conductor capacity where the original installation was single-phase loaded. Inrush is the most common cause of nuisance breaker trips after a retrofit.
Q12. Will the new fixtures be lighter or heavier?
Usually lighter, but the mounting method must be checked either way. A lighter fixture on an old fixing may need a new bracket, and a fixture with a different body shape may not fit an existing aperture or bracket spacing.
6. Project and delivery
Q13. What information do you need to quote a project?
Four things: the room dimensions and reflectance, the mounting height and method, the required maintained illuminance and uniformity, and the operating hours and tariff. With those four inputs our project group can return a fixture schedule, a layout drawing and an energy and payback figure.
Q14. Do you supply photometric files and layout support?
Yes. We supply IES photometric files for every catalogue fixture and can return a photometric layout with illuminance contours for a stated room. Where the project has an existing specification, we can check our fixture against the stated maintained illuminance rather than quoting an initial figure.
Q15. Can fixtures be supplied with a specific CCT and beam per zone?
Yes. Colour temperature, beam angle and CRI can be specified per zone on a single order, and where a continuous installation requires colour consistency across a delivery split into several batches, hold to one chromaticity bin and state that requirement at the order stage.
7. Part numbers in this FAQ
The industrial high-bay family runs from Z-05 to Z-08, covering narrow and wide distributions for different mounting heights, and the tri-proof and linear industrial fixtures are in Z-10 to Z-13. Outdoor and area lighting sits in Z-16 to Z-20 depending on the mounting and the distribution. Because these fixtures use the same package families as the component catalogue, the thermal and lifetime questions in the LED FAQ apply here as well.
8. Related resources and next steps
Send a project with the four inputs above and our project group will return a layout, a schedule and an energy figure. For the vocabulary behind these answers, see the LED package and reliability glossary, and for the electrical questions see the LED diode and chip FAQ.
Lifetime and Maintenance Questions
| Code | Meaning | Typical claim |
|---|---|---|
| L70B50 | 70 percent flux, 50 percent of population | 50,000-100,000 h |
| L80B50 | 80 percent flux, 50 percent of population | 35,000-60,000 h |
| L90B50 | 90 percent flux, 50 percent of population | 20,000-40,000 h |
| L90B10 | 90 percent flux, only 10 percent below | Premium industrial parts |
Q16. What is the difference between L80 and L70?
The flux threshold. Industrial and retail environments usually specify L80 for visual comfort; warehouses with wide spacing can accept L70 because the uniformity grid, not raw flux, sets the design.
Q17. What does B10 versus B50 change?
B is the fraction of the population allowed below the L threshold. A B10 claim is a tighter manufacturing promise than B50 and is what large continuous installations should demand.
Q18. Why do datasheets cap TM-21 extrapolation?
Beyond six times the LM-80 test duration, measurement error dominates the projection. A 6,000-hour test supports a 36,000-hour claim; longer claims need the 10,000-hour test or field data.
Retrofit and Controls Questions
Retrofit economics fail on inputs nobody measured. Five values decide whether an LED conversion pays back in one season or three years:
| Input | Why it matters | How to get it |
|---|---|---|
| Existing lumens per fixture | Sets the one-for-one swap target | Old datasheet or photometry file |
| Mounting height | Distribution changes with optics | Site survey with a laser meter |
| Ambient temperature | Driver and LED derating | Log a summer week at the fixture |
| Controls protocol | 0-10 V, DALI or sensor-native | Check the driver specification |
| Energy price and hours | Payback denominator | Utility bill times lighting schedule |
Q19. Can I keep the HID ballast when converting?
Only with LED tubes and drivers specifically rated for ballast compatibility, and only after checking the ballast list. Direct-wire conversions are more reliable and are what we recommend for high-bay.
Q20. Will legacy dimmers work with LED retrofits?
Triac dimers designed for resistive loads cause flicker below 20 percent output. Plan a 0-10 V or DALI driver wherever dimming is more than an occasional on-off.
Q21. Do occupancy sensors still pay back after LED conversion?
Yes, but the arithmetic changes: with 60 percent lower power, sensor savings shrink in absolute terms, and controls should be justified on maintenance hours as much as energy.