Most machine vision cameras bring one or more strobe outputs out on their I/O connector, and the tempting move is to wire a small LED light straight to them and leave the light controller in the box. Sometimes that works. More often the pulse comes out dim, the image flickers, or the output dies after a few weeks. The difference is one comparison: the light's rated drive current against the camera's per-channel output current. This guide gives you the formula, a worked 24 V example, the wiring that holds up in production, and the point at which a light controller becomes the right answer.
What a camera strobe output actually is
A strobe output is a transistor switch inside the camera, timed to the sensor so the pulse lands inside the exposure. It is not a power supply. On most cameras it is a logic-level signal of 3.3 V or 5 V that carries a few tens of milliamps — enough to feed the trigger input of a dedicated controller and nothing more; the case for that dedicated box is made in why your vision light needs a controller. A second class of cameras fits a stronger buffered output, good for a few hundred milliamps. In both cases the number that decides the wiring is not the voltage but the per-channel output current printed in the camera's I/O specification.
A third, smaller group integrates a genuine driver stage rated in amps — about 3 A per channel is the figure that class prints — with the light's supply riding in through the camera's own power input. Such a camera is a small strobe controller in its own right, but it is a capability to read off the I/O sheet, never to assume. When the light feeds from the camera's supply, the camera's power budget joins the arithmetic, and the camera power guide for USB versus external 5 V covers that side.
The two numbers that decide it
Direct drive works when the load fits the switch, so put both sides in amps.
The light's side is its rated drive current at the supply voltage you will run. Constant-voltage 24 V lights print a power rating, and the power equation turns it into current:
A 4 W, 24 V light asks for 4 ÷ 24 = 0.17 A on every pulse. That is the peak pulse current, and duty cycle does not reduce it: a 10% duty cycle cuts average power and heat, but the switch carries the full current while the pulse lasts. Duty cycle matters for the driver's own heating and for LED lifetime, which the strobe duty cycle guide works through.
The camera's side is the per-channel output current from its I/O specification: tens of milliamps for a logic output, up to a few hundred for a buffered one. Against that, apply the margin that keeps a transistor switch alive across part tolerance, temperature and cable drop: treat 80% of the printed rating as the usable budget. A 100 mA output is an 80 mA budget. Above the budget, the decision makes itself.
Worked example: a 4 W, 24 V spot light against a 100 mA camera output
The inputs, with their sources:
- Light: the LS-SPT-0133, a third-generation spot light rated 4 W at 24 V (catalog data).
- Camera output: 100 mA per channel — an example figure standing for a buffered output; substitute the number printed in your camera's I/O sheet.
- Margin rule: 80% of the printed rating.
The rule in words: divide the light's rated power by its supply voltage, multiply the output rating by the margin, and compare the two currents.
The arithmetic:
- Drive current: 4 W ÷ 24 V = 0.167 A ≈ 170 mA.
- Usable output budget: 100 mA × 0.8 = 80 mA.
- Overload: 170 ÷ 80 = 2.1.
The output transistor is asked to carry more than twice its rating on every pulse. The first symptom is a drooping pulse — the light glows dim and image contrast drifts from frame to frame. Run that way for long and the switch fails, taking the station's only light with it.
The decision: this light does not belong on a camera output. At 170 mA it misses the 80 mA budget by a factor of two, so it runs on a controller channel, or you choose a light that carries its own trigger driver.
- Output
- Constant voltage 24 V
- Channels
- 4 channels
- Control
- Digital
The compact controller above is rated 60 W across 4 channels, which is 15 W per channel — 0.63 A at 24 V, nearly four times the 170 mA the light needs — so the load runs without ever approaching the driver's limits.
Which loads a camera output can carry
Applied to the load classes that turn up at a vision station, at 24 V, with each verdict judged against the 80% budget (20 mA for a 25 mA logic output, 80 mA for a 100 mA buffered output, 2.4 A for a 3 A driver stage):
| Load | Current at 24 V | Logic output, 25 mA | Buffered output, 100 mA | Driver-stage camera, 3 A |
|---|---|---|---|---|
| Indicator LED board, 0.5 W | 21 mA | no | yes | yes |
| Small spot, 3 W | 125 mA | no | no | yes |
| Small spot, 4 W | 167 mA | no | no | yes |
| Compact bar, 12 W | 500 mA | no | no | yes |
| Multi-die bar, 50 W | 2.1 A | no | no | yes |
Each column head is an example figure for a class of output; the number printed for your camera replaces it, and the verdicts move with it. The pattern does not: only indicator-class loads clear a logic output, and everything from a 3 W spot upward wants either a buffered output on a very small light or a proper driver. The 3-5 W parts sit in the spot lights category, and longer arrays belong to the bar lights category and to a controller channel.
Direct drive earns its keep on single-light, small-load stations: a presence check beside the camera, a bench rig, a compact head where a controller box will not fit. The hardware side of that constraint is covered in the compact lighting guide.
Wiring the direct connection
Three wirings cover every case.
- Camera output to a light's trigger input. The light keeps its own fused supply and its own driver, and the camera carries only the few milliamps the input needs. Match ground references when the output is not isolated, keep the signal pair short and twisted, and check the input's threshold voltage before assuming a 3.3 V pulse will fire it.
- Camera driver-stage output to the light's supply input, on cameras whose I/O sheet prints an amp-level rating. Follow the printed pin, wire gauge and fuse guidance, keep the run short, and size every connector and conductor for the pulse current — the same arithmetic used for sizing 12 V LED load wiring, applied here at 24 V. Which connector carries which current is tabulated in the controller-to-light cable adapters guide.
- A bare LED and resistor on a GPIO pin, for indicator-class LEDs only. Within its current budget, a camera output can switch a single LED and its resistor directly; anything brighter wants a transistor stage, and the GPIO MOSFET drive guide works the resistor sizing.
Whichever wiring you choose, the pulse still has to land inside the exposure. A light that fires late, or a trigger polarity set backwards, produces a black or half-lit frame that looks exactly like a dead light; the black-frame timing guide walks that diagnosis. The strobe rise time guide explains why the first microseconds of a pulse contribute less light than the last, which matters once pulses get short. Enabling and wiring the output itself is covered step by step in the smart camera strobe output guide.
Lights that take a trigger signal instead
The cleanest direct connection is not a power connection at all. Many spot and bar lights carry a trigger or strobe input plus a driver of their own: the camera supplies a logic signal, the light's driver switches the LED current, and the camera's output budget stops mattering. Two details still need checking — the input's threshold voltage, and a supply and ground reference that exist independently of the camera. What changes inside the light is explained in the integrated strobe drivers guide.
- Size
- 50-100 mm
- Voltage
- 24 V
- Wavelength
- 405 nm
A light such as the LS-SPT-0068, with its PNP trigger input, is wired for exactly this arrangement: the camera's strobe line signals the pulse, the light's driver handles the current, and the camera never sees the load.
What you give up without a controller
Current is only part of what a controller does. Skip it and you also skip:
- Regulation. A camera output switches whatever the supply rail delivers. Constant-voltage drive lets brightness drift as the rail sags and the LEDs warm, while constant current holds it steady; the drift mechanism is worked through in the constant current versus voltage guide.
- Overdrive. Controllers raise the pulse current above the continuous rating to buy brightness in short pulses. A camera output has no current control to raise; the technique and its guardrails are in the overdrive and current control guide.
- Sequencing. Photometric stereo and multi-light stations fire channels in timed order, which is what the multi-channel sequencing guide is built around.
- Isolation and clean power. Controller channels switch from their own supply with the logic side separated from the load, keeping the camera's I/O electronics out of the load's current path.
None of this matters for an indicator-class blink. All of it matters once the light's output has to stay constant across a shift, or several lights have to fire in a fixed order. Where currents step up, so does the hardware:
- Output
- Constant voltage 24 V
- Channels
- 4 channels
- Output
- Constant current
- Channels
- 2 channels
The LS-CTL-0341 is a 4-channel digital power supply controller with an 8.3 A total output budget. Split evenly, that is about 2 A per channel — roughly twenty times a 100 mA camera output. The LS-CTL-0054 is a 2-channel high-power constant current controller rated 240 W per channel, the class that runs long, high-output bars.
When the usual answer is wrong
Three cases flip the default.
A camera that prints an amp-level driver rating really can carry a small light. Against a 3 A stage, the worked example's 170 mA load sits at about 6% of the rating, and direct drive is simply the right answer — same 80% margin, wire to the printed gauge.
A light with a trigger input turns the question from amps into logic levels. The camera supplies a signal, the light supplies the current, and the checks shrink to threshold voltage and a common reference.
And a station that fails on timing rather than current — the light fires at the wrong moment, frames alternate bright and dark — is not rescued by any amount of current headroom. That is trigger and exposure alignment, set out in the camera strobe output timing guide.
Checks before you skip the controller
- Per-channel output current in the camera's I/O specification — the rating the switch actually enforces. Check the total I/O budget too when two outputs fire together; a per-channel figure does not license doubling.
- The light's rated current at your supply voltage, converted from its printed watts with I = P / V.
- The 80% comparison — light current against the derated budget; the wiring decision falls out of it.
- The trigger input's threshold voltage, if the light has one; a 3.3 V pulse does not reliably drive a 24 V PNP input.
- A ground reference or an isolation plan, because a non-isolated output plus a floating light supply makes a trigger that never fires.
- Conductor and connector sizing for the pulse current, not just the average.
- The pulse inside the exposure window, confirmed on the bench with the camera's strobe timing tools before the station ships.
If the two numbers fit, wire it and move on to the application. If they do not, the light controller finder narrows the catalog by channels, output type and strobe feature, the lights finder pairs the light to it, and the lighting topic page collects the rest of the wiring and timing guides.
The configurator matches a camera, lens, light, light controller and cables to each other, step by step, and lists only parts that fit what you already picked.
Questions
What happens if a light draws more current than the camera output can supply?
The failure is progressive rather than instant. During each pulse the output transistor comes out of saturation, so the rail sags and the light fires dim and short — image contrast drops first. Run that way for weeks and the switch overheats, failing intermittently at first and then for good. Because the image merely loses contrast or goes dark, the fault is easy to misread as an exposure or lens problem. Comparing the two currents before wiring prevents the whole sequence.
Does strobe duty cycle let me exceed the camera output's current rating?
No. Duty cycle sets how often the pulse repeats, not how hard the switch works during each pulse. A 10% duty cycle cuts average power to a tenth, but the camera's output still carries the light's full peak current for every millisecond it conducts. Duty cycle matters for the light driver's heating and the LED lifetime, not for the output's current rating, so the sizing comparison stays at peak current against the printed figure.
What is the difference between a trigger input and direct drive on a light?
A trigger input is a logic signal that tells the light's own driver to switch; direct drive makes the camera's output carry the LED current itself. The trigger needs only a few milliamps at the input's threshold voltage, so almost any camera can use one. Direct drive carries the full load current, so it works only when the light's rating fits the printed per-channel budget, and the light's supply stays separate from the camera.
Can a 3.3 V camera output trigger a 24 V PNP light input?
Often not, and it catches more stations than current limits do. A PNP input generally waits for a voltage near its supply rail before it fires, and a 3.3 V logic pulse sits far below that threshold, so the light never strobes at all. Read the input's voltage requirement on the light's data sheet, then either choose a light whose input accepts logic levels or add a transistor stage between the two.
Do I still need a controller if my camera has a direct drive feature?
For a small light within the printed current rating, no — the camera replaces it. What you give up is constant-current regulation, strobe overdrive, channel sequencing and an isolated power stage, so brightness stability across a shift and multi-light timing fall back on the camera. If the station needs any of those, or the light draws more than the rating allows, a controller channel stays in the build.