Difference and Relationship Between UV Curing Units (mJ/cm²) and (mW/cm²)
I. Concept of UV Curing
Difference Between (mJ/cm²) and (mW/cm²)
▲ W/cm² and mW/cm² are intensity units, representing the power per unit area, which means the instantaneous irradiation strength.
Energy Units: Joule (J), millijoule (mJ)
The energy unit of light intensity can also be expressed as:
J/m² or mJ/cm², which represents the amount of light energy per unit area.
▲ J/cm² and mJ/cm² are energy units, representing the total accumulated energy per unit area.
The relationship between them is:
Energy = Intensity × Time, which is the most fundamental conversion formula.
To understand the difference between energy (mJ/cm²) and intensity (mW/cm²), the key point is that one represents the total amount, while the other represents the rate.
Energy Density vs Intensity – Comparison
|
Feature |
Energy Density |
Intensity |
|
Concept |
Total energy received per unit area |
Power received per unit area (rate of energy) |
|
Physical Meaning |
Accumulated energy, i.e., the total work done |
Instantaneous value, i.e., the rate at which work is done |
|
Unit |
Millijoules per square centimeter (mJ/cm²) |
Milliwatts per square centimeter (mW/cm²) |
|
Analogy |
Total amount of water: how much water has flowed |
Water flow speed: how fast the water flows |
|
Calculation Formula |
Energy = Intensity × Time |
Intensity is the instantaneous measured value |
Additional Notes
In the UV curing/UV printing industry:
Intensity (mW/cm²) → determines curing speed
Energy Density (mJ/cm²) → Determining whether curing is complete
Relationship formula:
Energy(mJ/cm2)=Intensity(mW/cm2)×Time(s)
II. Concept of UV Curing
Relationship Between (mJ/cm²) and (mW/cm²)
1. The relationship between the two is connected by a basic formula in physics:
Energy = Power × Time
For these specific units, the conversion relationship is:
• Basic Relationship:
1 mW/cm² × 1 second = 1 mJ/cm²
• This means that if the irradiation intensity is 1 mW/cm² for 1 second, the accumulated energy is 1 mJ/cm².
• General Formula:
Energy (mJ/cm²) = Intensity (mW/cm²) × Time (seconds)
2. Common Conversion Formulas
1 Joule (J) = 1 Newton·meter = 1 Watt (W) / second (S)
1 J/cm² = 1000 mJ/cm² = 1,000,000 μJ/cm²
1 J/m² = 1000 mJ/m² = 1,000,000 μJ/m²
1 J/m² = 0.1 mJ/cm²
1 W/m² = 1000 mW/m² = 1,000,000 μW/m²
1 W/m² = 1000 mW / 10000 cm² = 0.1 mW/cm² = 100 μW/cm²
1 W/m² = 0.1 mW/cm²
1 mW/cm² = 1000 μW/cm² = 10 W/m²
III. Practical Application Scenarios
In real-world applications, these two concepts each have different focuses:
▲ Intensity (mW/cm²)
This is usually determined by the equipment itself and the irradiation distance. It indicates how strong the UV lamp’s instantaneous output is. When using a UV radiometer (UV energy meter), the value displayed on the screen in real time is usually the intensity.
▲ Energy (mJ/cm²)
This is the core parameter in many industrial processes. Many research studies and industrial procedures (such as UV disinfection, photocuring, and biomolecular crosslinking) clearly specify the required energy dose. For example:
“The irradiation energy must reach 100 mJ/cm².”
In this case, the required energy dose is achieved by controlling the irradiation time.
⚠️ Important Note:
Simply multiplying a peak intensity value measured at a certain moment by time to calculate total energy may overestimate the actual accumulated energy. This is because UV lamp intensity may fluctuate, or the energy distribution within the irradiation area may be uneven.
The most accurate method is to use a UV energy meter to measure in real time and directly read the accumulated energy value.