UV Curing: Terms & definitions, every question, answered
30 answers below, written from the manufacturer's manuals and our own bench experience. Prefer to tap through them? The same answers power the live chat in the corner. Ready to buy? See the systems or request a quote.
What does irradiance mean?
The optical power landing on a surface per unit area, expressed in W/cm² or mW/cm². It describes how intense the light is at the work, our SunSpot 2, for example, delivers over 18 W/cm² of UVA.
What does J/cm² measure?
Joules per square centimeter, the unit of dose, or energy density. One second of exposure at 1 W/cm² delivers 1 J/cm².
mW/cm² vs W/cm², what's the difference?
Just scale: 1,000 mW/cm² equals 1 W/cm². Flood systems are usually quoted in mW/cm² and spot systems often in W/cm², so convert before comparing numbers.
What does dual-cure mean?
A chemistry with two curing mechanisms, UV plus a secondary such as moisture, heat, or an activator, so material the light cannot reach still cures. It is the standard answer for shadowed geometry and deep sections.
What does tack or tack-free mean?
Tack is residual surface stickiness after exposure, usually oxygen inhibition or under-cure. A tack-free surface is fully polymerized at the top; datasheets often quote dose to tack-free separately from dose to full cure.
What is potting?
Encasing a component or assembly in a protective resin. UV potting cures in seconds per pass rather than oven hours, within the depth the light can reach.
What is staking?
Locking a component, wire, or fastener in place with adhesive at discrete points so it survives vibration and handling, reinforcement rather than a structural joint. It is one of the highest-volume spot-curing applications.
What does tacking mean in assembly?
A quick, partial-strength adhesive fix that holds parts in position for later processing, a one-second UV exposure typically does it. Distinct from staking, which is a permanent reinforcement.
What is conformal coating?
A thin protective polymer film applied over a circuit board to guard against moisture, dust, and contamination. UV-curable versions cure in seconds, and spot sources handle repairs and touch-ups on them.
What is UVA?
Ultraviolet from 315–400 nm, the least energetic UV band and the workhorse for curing, where most industrial photoinitiators absorb. Our LED wavelengths of 365–395 nm sit within it, and 405 nm sits just past its visible edge.
What is UVB?
Ultraviolet from 280–315 nm, present in broad-spectrum arc output but absent from UVA LEDs. Some chemistries use it for surface cure; biologically it burns skin and eyes at lower doses than UVA.
What is UVC?
The 100–280 nm band, the most energetic UV, emitted in small amounts by broad-spectrum arc lamps and not at all by our LEDs. It drives surface cure and germicidal effects, injures tissue quickly, and can create ozone.
What does UVV refer to?
The violet edge of visible light, roughly 395–450 nm, labeled UVV in curing specs. Some photoinitiators absorb there, which is what 405 nm LEDs and the visible content of arc lamps exploit for depth of cure.
What is an arc lamp?
A source that makes light from an electrical arc sustained in a pressurized gas, in curing, a mercury short-arc lamp whose plasma emits intense broad-spectrum UV and visible output.
What is an LED array?
Multiple LED dies mounted and driven together to reach higher output than a single emitter, sharing a heat sink and coupling optics. Curing LED heads are compact arrays rated by peak wavelength.
What does duty cycle mean?
The percentage of each cycle the source spends actually emitting, a 2 second exposure every 10 seconds is 20% duty. It drives lamp-hour consumption, heat load, and the arc-versus-LED economics.
What does depth of cure mean?
How far below the surface the material fully polymerizes in one exposure, limited by how strongly the formulation absorbs the cure light. Broad-spectrum and longer wavelengths reach deeper; around 5 mm per pass is a practical ceiling for typical encapsulants.
What is shadow cure?
The ability of certain chemistries, notably cationic epoxies and dual-cure systems, to keep polymerizing in areas the light never reached after an initial exposure. Standard acrylates do not shadow-cure; light-blocked acrylate stays wet.
What is a light guide's acceptance angle?
The cone of input angles the guide can capture and carry by total internal reflection, set by the core and cladding refractive indices (its numerical aperture). Light launched outside the cone is lost, one reason lamp-to-guide coupling optics matter.
What does reciprocity mean in curing?
The rule of thumb that dose equals intensity times time, so half the intensity for twice the time gives the same cure. It holds broadly but not perfectly, very low intensity may never overcome oxygen inhibition regardless of time, so validate at production intensity.
What does spot size mean exactly?
The diameter of the illuminated area at the work surface, set by guide core, optics, and working distance, ours range from about 2 to 12 mm. Quote it together with working distance, since the beam diverges past the tip.
What does nm mean in curing specs?
Nanometers, the unit of light wavelength. Curing wavelengths run from deep UV near 250 nm up through visible violet around 405–450 nm; the number tells you where in that range a source emits.
What is crosslinking?
The formation of chemical bonds linking polymer chains into a rigid network, the reaction UV exposure triggers via the photoinitiator. Crosslink density is what turns a liquid adhesive into a solid with strength and chemical resistance in seconds.
Acrylate vs cationic epoxy UV chemistry?
Acrylates cure by free radicals, very fast, but oxygen-inhibited at the surface, and they stop curing when the light stops. Cationic epoxies cure by an acid mechanism that continues after exposure (shadow cure), with lower shrinkage but moisture sensitivity during cure.
What is a shutter, in curing terms?
A mechanical blade that blocks or passes the beam of a continuously running arc lamp to create timed exposures. LED systems do not need one, the source itself switches instantly.
What is a safety interlock?
A switch circuit that disables the UV source whenever a guard, door, or enclosure panel is open. The SkyBeam provides a dedicated interlock input for cell guarding.
What's the difference between power and irradiance?
Power (watts) is a source's total output; irradiance (W/cm²) is how much of it lands per unit of surface area at the work. A 200 W lamp focused into a 5 mm spot produces enormous irradiance, the number that actually cures parts.
What is peak wavelength and FWHM for an LED?
Peak wavelength is where an LED's output is strongest, 365, 385, 395, or 405 nm on our heads, and FWHM (full width at half maximum) describes how narrow the band is, typically 10–20 nm. Together they define whether the LED overlaps your photoinitiator's absorption.
What does working distance mean?
The gap between the guide tip (or lens) and the work surface. Because the beam diverges, working distance sets spot size and irradiance together, fixture it, document it, and keep it constant.
What is output drift?
The slow decline or variation in delivered intensity as lamps age, guides solarize, and optics get dirty. It is countered by scheduled radiometer checks against a baseline and planned replacement of consumables.
