Spot size and working distance are inseparable variables in UV spot lamp specification. A spot size without a working distance is meaningless — the spot expands with distance, so the same lamp delivers a 5 mm spot at 10 mm and a 15 mm spot at 40 mm. A working distance without a spot size tells you nothing about whether the cure zone covers the bond area. Engineers who specify both together — at the same conditions — get quotes that are directly comparable and equipment that performs as expected in production.
Why Specifying Both Together Matters
UV LED spot lamp manufacturers optimize their lamps to perform at defined conditions. When an RFQ asks only for “spot size” or only for “working distance,” suppliers respond with specifications measured at their preferred conditions, which may not match your process — Supplier A might specify a 5 mm spot at 10 mm working distance, Supplier B an 8 mm spot at 30 mm, and without both values for the same system you cannot compare the two or predict what either delivers at your actual production conditions. Our explainer on how work distance affects UV irradiance at the cure point covers why this relationship is nonlinear and why it must be pinned down at the RFQ stage, not after equipment arrives.
How to Define Your Production Conditions First
Before writing the RFQ specification, determine two things. First, the required working distance — the gap between light guide tip and adhesive surface in your actual production fixture, set by part clearance needs, the height of features the guide must clear, fixture arm reach, and operator access. If the fixture isn’t designed yet, give the supplier a target range (“15–30 mm, with 20 mm preferred”) rather than a single point, so they can provide irradiance-versus-distance data across it. Second, the required cure zone — the diameter or maximum dimension of the bond area, which sets the minimum spot size needed at the specified working distance; our guide to what spot size you need from a UV LED system walks through this calculation for common bond geometries. A circular 10 mm bond area, for instance, requires the spot to deliver irradiance above the adhesive’s minimum across that full 10 mm diameter at the production working distance.
Writing the RFQ Specification
Once production conditions are established, write the specification as a combined requirement. A point specification, naming a single working distance, might read: “Spot diameter: minimum 12 mm at 20 mm working distance from the light guide tip, measured at the irradiance contour corresponding to 80% of peak irradiance.” This form is clear, unambiguous, and directly testable. A range specification instead asks the supplier for irradiance-versus-distance data across several working distances (for example, 10, 20, and 30 mm), including spot diameter and peak irradiance at each — giving the supplier more flexibility in presenting their product and giving you the data to pick the best-fit working distance yourself. Our guide to how to specify UV LED equipment in a procurement RFQ covers the broader RFQ structure these specifications fit into.
Spot size without irradiance is incomplete, since a large spot with insufficient irradiance still fails to cure the adhesive — so write wavelength, irradiance, and spot diameter together in one combined specification, along with the measurement method (calibrated radiometer, wavelength, calibration traceability) the supplier should use to verify it. A specification that names all of these is directly testable, rather than open to interpretation on delivery.
If you would like assistance writing a combined spot size and working distance specification for your application, Email Us and an Incure applications engineer will help you define the requirements based on your adhesive system and bond geometry.
Requiring Beam Profile Data and Setting Acceptance Criteria
Nominal spot size claims from suppliers may be based on theoretical calculations or idealized conditions, so request actual beam profile data — a map of irradiance as a function of radial position across the spot — at your specified working distance, presented both graphically and in tabular form. A beam profile curve reveals whether the irradiance distribution is smooth (Gaussian or flat-top) or carries hotspots and cold regions; adhesive cured under a spot with a central hotspot and low-irradiance edges will cure unevenly — overcured center, undercured edges — even if the nominal spot covers the bond area.
Include acceptance test criteria in the RFQ so delivered equipment is verified against firm numbers at your own facility: peak emission wavelength within a defined tolerance, irradiance at the specified working distance, and irradiance across the required diameter measured at several radial points, with equipment failing any criterion returned to the supplier at their expense. Clear acceptance criteria make the purchase order a contract on performance, not just on equipment delivery.
What Suppliers Should Provide in Their Response
A complete supplier response to a spot size and working distance specification should include:
- Irradiance at the specified working distance (center, measured value)
- Spot size at the specified working distance (contour at the specified irradiance threshold)
- Beam profile data at the specified working distance
- Light guide diameter used for the specified configuration
- Working distance range over which the lamp meets the specification
- Measurement method, calibration standard, and measurement uncertainty
Suppliers who cannot provide this level of data are not equipped to confirm that their product meets your specification — a signal to evaluate them carefully or request a demonstration unit before committing to a purchase.
Documenting the Agreed Specification After Purchase
Once the lamp is purchased and delivered, document the confirmed spot size and working distance as controlled process parameters:
- Record the measured irradiance at the production working distance (not the supplier’s catalog value)
- Record the measured spot diameter at that irradiance threshold
- Document the working distance as a controlled parameter for fixture setup and maintenance
- Establish periodic re-verification of irradiance at working distance to confirm lamp performance has not degraded
This documentation becomes the basis for production process validation and for detecting lamp aging that would push irradiance below the required minimum.
Contact Our Team to discuss UV LED spot lamp specification for your production process or to request application testing at your specified conditions.
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