Light flashes then goes out on power-up? Usually a protection trip, not a dead driver. This guide separates four protections and shows what to check first.
A luminaire that lights for a moment then goes dark on power-up is most often not a dead driver or a failed LED; it is the driver protecting itself. Modern LED drivers carry multiple protections: detect an anomaly, cut the output, and recover when it clears. Reading the time structure of "flash then die" saves a wrong return.
The one-sentence rule: it is a protection trip, not a corpse
"Flash then die" = output builds on power-up, then the protection circuit detects an anomaly and cuts output
It is recoverable, and is a different animal from "no output at all" (driver or upstream open)
Four usual triggers: under/over-voltage lockout, over-current/short, over-temperature, soft-start inrush
The first move on site is not to swap parts but to bisect: remove the load and see if it still flashes
Power-up timeline: what that one flash means
It lit once, so startup is OK; the cut happens after protection samples an anomaly, pointing at four sources
The four protection triggers
1. Under/over-voltage lockout (UVLO / OVP)
The driver has an input voltage window. If the input has not settled into range at power-up, or a grid spike overshoots, the chip locks out:
Typical threshold: under-voltage lockout below about 85% of rated input, over-voltage protection above the upper limit
Sign: at the far end of a long run in a remote site, low voltage locks out on every start
If it just protected, the case has not cooled, or it sits in a sealed hot cavity, temperature over the threshold (most units 85-105 deg C case) locks it:
Sign: first cold start stays lit longer; repeated power cycles die faster and faster
Sealed boxes, direct sun, no clearance to the ceiling are the main causes
On-site bisection: drop the load first, then split by environment
Drop the load to decide driver-side versus load-side before swapping anything
How it differs from no output at all
Flash then die: the driver started, protection acted after start - fault is in sensing, protection, load or environment
No output: the driver may never have started, or upstream has no power, a fuse blew, wiring is open - follow the no-output five-step diagnosis
Do not keep hard-cycling just because "it lit once": every protection trip stresses the power devices, and in a sealed box a "protection" can become a "real failure"
On-site handling checklist
Drop the load first: no-load stops flashing means load or wiring; no-load still flashes means driver or input
Check short and polarity: meter the output for a short and confirm LED polarity is not reversed
Retry cold to judge OTP: wait five minutes, if it stays lit longer then dies, it is over-temperature; move to ventilation or derate
Measure input voltage: if the far end is low, fatten the wire or move to 48 V, see 24V or 48V, when to switch
Leave front-end margin: start-up inrush of many units adds up; breaker and soft-start window need headroom, see sizing the AC breaker and cable
Do not grind it: if the same unit flashes and dies three times with no recovery, stop powering and swap the part the bisection points to
Power, wire size and inrush math are assisted by the LED driver sizing calculator; for a batch showing the same symptom, check first whether they share one environmental cause.
Do not keep cycling a unit that flashes and dies; every protection trip is a stress event. Send us the wiring diagram, LED count and the environment (sealed, hot?), and we will say whether it is a wiring fault or a sizing problem. Contact →