Voltage drop on long runs: it is the cable
There is one formula for single phase: ΔU ≈ 2 × I × L × ρ / A, with ρ = 0.0175 Ω·mm²/m for copper. Twenty 150 W fixtures at the end of a 30 m run draw about 13 A, and on 2.5 mm² that is roughly 5.5 V, or 2.4% of 230 V. Stretch the same load to 40 m and it becomes 7.3 V, over the line. This is a wiring parameter, not a fixture parameter, but what the customer sees is that the lights are dim.
Get a QuoteKey parameters
| Power | 100–200 W |
|---|---|
| Luminous flux | 12,000–25,000 lm |
| IP rating | IP66 |
| Input voltage | 220–240 V |
| Frequency | 50 / 60 Hz |
| Allowed voltage drop | ≤ 3% end to end, AC side |
| Suggested cable / run | 2.5 mm² over 30 m, about 20 × 150 W |
Voltage is the item most often skipped
This page is 220–240 V at 50 / 60 Hz. Wide-range input is not about "works anywhere" — it is about not derating or tripping when the supply sits low or high. In regions with unstable grids, narrow-range drivers fail noticeably more often.
The other thing that gets skipped is inrush: when high-power fixtures start together the inrush adds up and trips the breaker. Where twenty units switch on at once, size the breaker on the row, not on one fixture — undersize it and the symptom is "it trips the moment you switch on", which few people trace back to the lights.
Voltage drop: right voltage, still dim
Allowed drop on this page is ≤ 3% end to end, AC side. It shows up worst on low-voltage and DC systems: a 24 V run of 30 m on 2.5 mm² can lose more than 10% by the far end, the fixtures visibly dimmer and the furthest ones dimmest. On site that looks like a faulty fixture; it is an undersized cable.
On the AC side the working figure is to keep total drop under 3%. That is a wiring parameter, not a fixture parameter — but it decides what the customer sees, so size the cable during the quote, not during commissioning when the lights get blamed.
Four things to verify before ordering
① Whether flux and efficacy are quoted for the complete fixture or the light source — a 10–15% difference that changes the fixture count. ② Whether colour temperature and CRI are measured or nominal values; mixed CCT within one batch is the most common arrival dispute. ③ Driver brand and model, plus its derating curve at high temperature — it is the only part that really sets life. ④ The mounting kit list: chain, bracket and anchors in the box, or the site stops for a day.
Concepts on this page
Need a Lighting Plan?
Tell us your scenario, Jie Zhai will help you choose.
Get a Quote All specification pages