Where do I get the absorbance figure?

From the substrate supplier, at the cure wavelength. Absorbance is exponential: 0.3 passes half, 0.6 passes 25%, 1.0 passes 10%.

Is clear plastic transparent to UV?

Usually not. Clarity is a visible-light property; polycarbonate absorbs below 380 nm and many clear films carry UV stabilizers on purpose.

What if the cure time comes out impractical?

Attack transmission rather than dwell, because transmission is exponential in absorbance. A longer-wavelength photoinitiator, another substrate grade, or curing from the other side all help.

Why is the safety margin larger here?

Because the bondline cannot be measured directly. The margin covers batch variation in absorbance, which no radiometer reading at the surface can close.

UV Curing calculator

UV Adhesive Bond Cure Time Calculator (Through-Substrate)

Work out the cure time for an adhesive that cures through a substrate. Enter the bondline dose target, incident irradiance, substrate absorbance and your safety margin.

What this calculator does

Find how long a UV adhesive needs when light must pass through a substrate to reach the bondline.

Formula used

Transmission = 10^(−absorbance)
Irradiance at the bondline = incident irradiance × transmission
Bare cure time = bondline dose target ÷ bondline irradiance
Cure time with margin = bare cure time × (1 + margin ÷ 100)
Times longer than a surface reading = 1 ÷ transmission

Inputs explained

Bondline Dose Target: Dose the adhesive needs at the glue line, from its datasheet.
Incident Irradiance at the Outer Surface: Radiometer reading on the outer face the UV enters.
Substrate Absorbance at the Cure Wavelength: Absorbance of everything between lamp and glue line, at the cure wavelength.
Process Safety Margin: Headroom over the bare requirement for batch variation and lamp ageing.

How to use the result

Best suited to curing through a lens, glass or housing, explaining a bond that failed despite surface dose, deciding between substrate grade and longer dwell.
Ignores scattering; a hazy substrate redirects light that still reaches the bondline. Ignores reflection at the entry surface, so the estimate is slightly optimistic. Assumes constant absorbance across a part that may vary in thickness.

Common questions

Where do I get the absorbance figure? From the substrate supplier, at the cure wavelength. Absorbance is exponential: 0.3 passes half, 0.6 passes 25%, 1.0 passes 10%.
Is clear plastic transparent to UV? Usually not. Clarity is a visible-light property; polycarbonate absorbs below 380 nm and many clear films carry UV stabilizers on purpose.
What if the cure time comes out impractical? Attack transmission rather than dwell, because transmission is exponential in absorbance. A longer-wavelength photoinitiator, another substrate grade, or curing from the other side all help.
Why is the safety margin larger here? Because the bondline cannot be measured directly. The margin covers batch variation in absorbance, which no radiometer reading at the surface can close.

Last reviewed 2026-10-01.