A UV spot lamp can read normal on its control panel while the bond line receives far less light than the process was qualified at. Measuring output on a schedule is how a line catches that drift before it shows up as under-cured parts.
Q: How Should You Measure the Output of a UV Spot Lamp?
A: Measure Irradiance at the Part’s Working Distance, Check the Lightguide Separately, and Log Every Reading
A useful measurement program has three parts. A radiometer reading at the working distance confirms what the bond actually receives. A lightguide transmittance check separates a failing guide from a failing source. A trend log turns individual readings into an early warning. For how the spot lamp hardware itself works, see Incure’s UV LED spot curing system explainer.
Choosing a Radiometer for Spot Work
A radiometer for spot lamp checks should meet a few practical requirements:
- Spectral response that covers your lamp. An LED unit such as the Incure L9000™ emits one band (365, 375, 385, 395, or 405 nm, depending on the unit). An arc lamp such as the Incure S20™ emits across 275–650 nm. Confirm with the instrument maker that the sensor reads in the band you use.
- Range that spans your readings. The L9000™ is specified from 7,500 mW/cm² at a 9 mm focal point down to 223 mW/cm² at 30 mm. The S20™ is rated at more than 21 W/cm² at the guide tip. A meter must handle the intensity at the position you measure without saturating.
- A sensor area suited to a small spot. The L9000™ spot measures 3 mm to 12 mm across its focal range, so the sensor should capture the spot you intend to measure.
Use the same instrument, or a documented equivalent, for every reading in a log. Changing meters mid-trend makes the trend meaningless.
Measure at the Tip or at the Working Distance?
Each position answers a different question.
At the working distance, the reading tells you the irradiance the bond receives. This is the number to compare against the adhesive’s dose requirement. Build a simple jig that holds the sensor exactly where the part sits, at the same distance and angle as the production fixture. On the L9000™, irradiance falls from 2,300 mW/cm² at 17 mm to 1,200 mW/cm² at 20 mm, so a jig a few millimeters out of position produces a misleading number.
At the tip, the reading reflects what the source and guide deliver before distance takes its share. Tip readings are useful for comparing lamps or guides on equal terms, and for diagnosing whether a drop comes from the equipment or from a fixture that has shifted.
Record both when troubleshooting. If tip output is steady but the working-distance reading has fallen, look at the fixture first.
Email Us with your lamp model and fixture layout, and Incure’s engineers can help set up a measurement point that matches production.
Testing Lightguides on Arc Systems With the LS217™
A lightguide can lose transmittance through a darkened liquid core, cracked fibers, or a contaminated connector face, while still looking intact. Incure’s LS217™ lightguide simulator gives a standardized reference reading at the delivery end so guide condition can be tracked on its own.
The LS217™ uses a Standard D (SMA-D) connector at Ø5 mm and is built for mercury arc, xenon, and halogen spot lamps, including the S20™. It is not compatible with LED spot lamps, which use a different port geometry. On an LED system, the working-distance radiometer reading is the primary check.
The LS217™ is a diagnostic tool, not a production part. It occupies the port briefly and comes out before production resumes. Incure’s product documentation suggests monthly checks as a baseline for lower-intensity work and weekly checks for high-intensity or tightly specified processes, plus incoming inspection of every new guide to set its baseline. It cites retiring a guide at 70–80% of that baseline as a widely used threshold, with the right figure set during qualification. Incure’s article on what causes UV light guide degradation explains the mechanisms behind the drop.
Building a Trend Log
A single reading is a snapshot. A log reveals direction. Record at minimum:
- Date, shift, and operator
- Lamp serial number and lightguide identifier
- Measurement position (tip or working distance) and jig ID
- Radiometer serial number
- Intensity setting on the controller
- Reading, and its percentage of the baseline
Set two lines on the chart: a warning level that triggers a closer look and an action level that triggers replacement or requalification. Base both on the dose margin your process actually has.
Reading the Trend Correctly
Different sources fade differently. The L9000™ is rated for 15,000 hours with less than 20% intensity decay, so a gradual slope over many months is expected; a sudden step points to damage, a fixture change, or contamination. Mercury arc bulbs are commonly replaced every 1,000 to 2,000 hours depending on duty cycle, and the trend log is a better guide to timing than the hour meter alone. After every bulb change, take a new baseline before production restarts.
When a reading drops, isolate the cause in order: fixture position, lightguide condition, then source. Each step uses a measurement you already have in the log.
Final Thoughts
Spot lamp measurement does not need to be elaborate. One radiometer, one jig at the real working distance, a lightguide check on arc systems, and a disciplined log cover the common ways output drifts. Contact Our Team to build an output-monitoring routine around your Incure spot curing equipment, and review Incure’s L9000™ lightguide and working-distance guide for distance-specific output data.
Visit www.incurelab.com for more information.