An LED is a current-controlled diode. The grid is voltage-controlled AC. The driver is the bridge, and it decides life expectancy, dimming behaviour and surge survival. In accelerated life testing of commercial LED luminaires, the failures showed up in the driver circuit, not in the LEDs.
Four ideas to carry into the next specification conversation you have.
Most LED drivers hold the output current in milliamps and let the output voltage settle where the string needs it, inside a declared window. Check the string voltage sits in that window at both temperature extremes.
LED tape and modular signage want a fixed DC bus, typically 12 V or 24 V, with each cuttable segment limiting its own current. NLC's SOLID strip publishes DC24V and electrical Class III.
Class I pairs basic insulation with a protective-earth connection; Class II uses double or reinforced insulation and does not rely on earthing (IEC 61140). The class is declared for the complete luminaire, not for one component, and SASO 2927 specifies Class I for road lighting in its scope.
Phase-cut for retrofit wiring (NEMA SSL 7A covers forward phase-cut compatibility), 1-10 V per IEC 60929 Annex E, DALI per IEC 62386, or PWM, which is both an accepted dimming input signal and the way a driver modulates its own output. Name the protocol, the minimum dim level and the curve, never just "dimmable".
Nine lines that turn "a good driver" into something a supplier can be held to. The Saudi rows are the requirements SASO sets for products in the scope of its road-lighting standard.
| Spec line | What the specification has to say | Where that comes from |
|---|---|---|
| Driver family | Constant current in mA, or a constant-voltage bus, with the output window | IEC 62384 · IEC 61347-2-13 |
| Lifetime | Hours + the survival fraction + the case temperature tc | Driver-maker practice (Signify white paper) |
| Power factor | ≥ 0.9, driver and integrated luminaire | SASO 2927:2019, products in scope |
| THD | < 15%, tested per IEC 61000-3-2 | SASO 2927:2019 · IEC 61000-3-2 |
| Surge | Two figures, L-N and L/N-PE. Road lighting in scope: 10 kV installation, 4 kV internal | SASO 2927:2019 · IEC 61000-4-5 |
| Shock protection | Class I or Class II, matched to the luminaire. Road lighting in scope: Class I | IEC 61140 · SASO 2927:2019 |
| Control interface | The named protocol, the minimum dim level and the dimming curve | IEC 62386 · IEC 60929 Annex E · NEMA SSL 7A |
| Flicker | Modulation depth AND frequency, measured, including at low dim levels | IEEE 1789-2015 (recommended practice) |
| Serviceability | Field-replaceable driver, the access method, and a dated spares commitment | ANSI C136.41 · SASO 2927 |
Where driver specifications are usually vague, and what a precise answer looks like.
Driver makers are explicit about this: the component most likely to fail in an LED driver is the electrolytic capacitor, and the driver's life is derived from it. Its temperature depends on the case temperature and on the ripple current through it, and roughly every 10 °C cooler doubles its life, the approximate rule of thumb capacitor and driver makers publish. That is why efficiency matters twice: the power a driver wastes becomes heat inside its own enclosure.
Ask for the minimum dim level the driver actually holds, the dimming curve, and the flicker at the bottom of the range. DALI's standard curve is logarithmic (IEC 62386-102, with curve selection in Part 218), so a percentage on the bus is a perceptual step, not a percentage of current. Judge flicker on modulation depth and frequency together, as IEEE 1789-2015 does, and measure it dimmed.
A dimmer and a driver are a pair, and there is a standard for exactly that: NEMA SSL 7A-2015, basic compatibility for a forward phase-cut dimmer with dimmable LED light engines. It does not cover reverse-phase (ELV) or 0-10 V. So a specification that says "dimmable" without naming the dimmer models the maker has tested is not a specification.
Hours, the survival fraction behind them, and the case temperature they were measured at. Driver lifetime is normally quoted to a 90% survival rate, and MTTF is a different number entirely, not a life expectancy. NLC's own catalogue already writes the LED side this way: L70B50 > 100,000 h and L80B20 > 50,000 h say different things about the same population. L is the retained-output threshold and B is the share of the population below it, so at 100,000 h at least half the units still give at least 70% of initial output, and at 50,000 h at least 80% of them still give at least 80%. The > puts those hour counts higher still. Because the threshold, the fraction and the hour count all differ, the two rows are not a ranking against each other. B is gradual light-output depreciation, so whether the driver is still running needs its own failure figure. And note the scope: LM-80 and TM-21 project the LED source, LM-84 and TM-28 work at luminaire level, and neither reports the driver.
If the driver is the part most likely to reach end of life first, specify how it gets replaced: a gear tray that withdraws, a connector instead of a potted loom, and a spares commitment with a date on it. Be precise about what the standard sockets cover, though. Zhaga Book 18 (Edition 4.0, 2025) standardises the socket between an outdoor luminaire and a sensing or communication node, and D4i standardises DALI inside the luminaire so a certified driver carries its data and powers the bus. Neither one makes the LED driver itself plug-replaceable: that stays a luminaire design decision. In SASO 2927 scope the receptacle on the roof is the 7-pin ANSI C136.41.
Our low-current systems work is built on Tridonic and Osram gear. On any fixture, ask for the driver datasheet, the tc-referenced life figure, the surge pair and the control protocol, and we will put them in writing.
Standards and manufacturer documentation behind every number on this page. The Saudi requirements are quoted from SASO's own workshop deck for the standard; the standard itself governs.
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