How to Specify Spot Size and Working Distance Together in One RFQ
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 specifies a 5 mm spot at 10 mm working distance. Supplier B specifies an 8 mm spot at 30 mm working distance. Without knowing both values simultaneously for the same system, you cannot compare these — and you cannot predict what either lamp will deliver at your actual production conditions. Specifying spot size and working distance together, at conditions representative of your production process, eliminates this ambiguity and produces comparable, actionable responses from suppliers. How to Define Your Production Conditions First Before writing the RFQ specification, determine two things: 1. The required working distance. This is set by your part geometry and fixture design. The working distance is the gap between the light guide tip and the adhesive surface in your actual production fixture. Factors that determine it: Physical clearance needed to load and unload parts without striking the lamp Height of components or features that the light guide must clear to reach the cure point Fixture arm length and adjustment range Operator access requirements If you have not yet designed the fixture, establish a target range: "working distance 15–30 mm, with 20 mm preferred." This gives the supplier a realistic range rather than a single point and allows them to provide irradiance-versus-distance data across the range. 2. The required cure zone. What is the diameter or maximum dimension of the adhesive bond area? This sets the minimum spot size at the specified working distance — the spot must cover the bond area with irradiance above the adhesive's minimum threshold. If the bond area is circular and 10 mm in diameter, the spot must deliver irradiance above the adhesive minimum across 10 mm diameter at the production working distance. Writing the RFQ Specification for Spot Size and Working Distance Once production conditions are established, write the specification as a combined requirement: Option 1: Point specification (single working distance) "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. Supplier to confirm irradiance at the 12 mm boundary at 20 mm working distance." This form is clear, unambiguous, and directly testable. The supplier must…