Stratasys/Objet contacted G&R Labs seeking a UV light meter designed specifically to measure intensity (mw/cm2) and energy (mj/cm2) on their 3D printer products. The Model 221 was created in that collaboration and remains the Stratasys/Objet standard measurement instrument when monitoring UV source output on those systems. It reflects the same measurement discipline G&R Labs brought to semiconductor fabs—traceable calibration, matched probes, and support from engineers who speak UV fluently.
Background: multi-jet printing and UV dose control
Objet-class printers cure photopolymer with UV lamps or LED arrays integrated into a complex scan path. Layer adhesion, shore hardness, and dimensional accuracy all depend on delivering the right dose per layer and over the build. When intensity falls, layers may under-cure; when energy is excessive, features can swell or support removal becomes difficult. Stratasys needed a meter operators could trust for factory service, field verification, and customer support—not a low-cost gadget with unknown calibration.
G&R Labs had decades of experience measuring mercury and broadband UV in manufacturing. Stratasys brought printer geometry, maintenance procedures, and acceptance criteria. The Model 221 merged those requirements into a single radiometer package with published specifications and NIST-traceable certificates on new units.
Design intent and specifications
The Model 221 measures the quantities maintenance manuals reference: intensity at the relevant plane and integrated energy over exposure intervals. Probe optics are chosen so readings relate to what the resin sees, not to an unrelated band that happens to produce a number. Electronics are designed for repeated recalibration over years—important because cables and connectors in busy service bays see real-world handling.
Interchangeability within the G&R probe family follows the rules documented on the Model 221 product page. After any repair that opens the probe or replaces wiring, recalibrate through calibration services so gain and offset match the NIST-traceable reference again. Stratasys user documentation for Objet systems discusses UV measurement expectations; align your internal SOPs with those guides and with the meter's certified performance.
Material tray changes, print mode changes, and head replacements can all alter the optical path even when the lamp hours counter looks healthy. A quick mw/cm2 check after those events costs minutes and prevents hours of failed builds. Store the fixture dimensions on the printer so every shift uses the same measurement geometry.
Field use, cleaning, and calibration
Service teams often discover contaminated filters when readings wander. Clean glass per How to Properly Clean Your Probe's Glass Filter before replacing lamps or adjusting power supplies. Log measurements before and after service to prove the optical chain returned to baseline.
If comparison against a second instrument disagrees, ask what standard each meter used at purchase and last recalibration—that is the same question George Richardson raises when customers wonder why two "identical" mw/cm2 displays diverge. See Fact or Fiction, Part 2 for the full calibration discussion and Buyer Beware for why unsupported meters cost more over time.
Factory service manuals for Objet systems assume a meter that responds like the Model 221. Substituting a bargain radiometer may still produce digits on a screen, but those digits will not align with Stratasys acceptance tables or with G&R calibration data archived for the instrument class. When auditors or OEM support ask for proof of UV output, a NIST-traceable certificate on a recognized model is the shortest path.
Train operators to store the probe with the cable loosely coiled, not sharply bent at the connector. The most common "meter fault" we diagnose is mechanical: broken conductors inside the cable after months of bench clutter. Repair is straightforward; the lesson is that metrology hardware deserves the same respect as a precision micrometer.
When Stratasys field engineers escalate UV-related tickets, the first question is often whether the customer meter still holds NIST traceability. Keeping the Model 221 on that calibration cycle prevents chasing software bugs that are actually dose drift.
Broader 3D printing metrology at G&R Labs
Objet platforms standardized on the Model 221; Autodesk Ember workflows use the companion Model 222. Both instruments sit on the same quality system: component inspection, calibration to NIST-traceable references, and direct phone support at (408) 986-0377. Visit Light Meters for 3D Printing for an application overview and Are All UV Light Meters the Same? if you are evaluating alternatives.
Conclusion
The Model 221 is not a rebranded generic radiometer—it is the product of an OEM collaboration where dose accuracy affects warranty, service, and customer outcomes. Treat it as part of the printer's metrology chain: clean probes, document fixtures, recalibrate after trauma, and call when process windows collapse.
Multi-site Objet fleets benefit when every service kit includes the same meter model and the same recalibration interval. Central quality can then compare mw/cm2 logs across plants without converting between unknown references—a practical advantage that shows up long after the initial purchase order is forgotten.
If you are drafting an internal work instruction, quote the Stratasys UV section alongside G&R calibration requirements so technicians see one coherent procedure rather than conflicting checklists. Include the certificate expiration date on the form so overdue recalibrations are caught before production lots run.
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Sources
- Stratasys Support — UV Measurement (Objet User Guide) (accessed October 22, 2026)
- NIST — Metrological Traceability (accessed October 22, 2026)
- RadTech — How to Measure UV Light (accessed October 22, 2026)
- NIST Physical Measurement Laboratory — Optical Radiation (accessed October 22, 2026)
- NIST — Calibration Services (accessed October 22, 2026)