Turn optical power into clear surface intensity values. Switch units and see precision controlled rounding. Download CSV or PDF reports for quick sharing anywhere.
Irradiance is radiant power per unit area. For uniform illumination, the irradiance E is:
E = Φ / A
Where Φ is radiant flux (watts) and A is illuminated area (square meters). If you enable angle correction, the calculator applies:
Etilted = (Φ / A) · cos(θ)
This cosine factor is commonly used for planar receivers with an incidence angle θ.
| Radiant Flux Φ | Area A | Angle θ | Computed Irradiance | Notes |
|---|---|---|---|---|
| 10 W | 0.5 m² | 0° | 20 W/m² | Uniform illumination across a half square meter. |
| 250 mW | 25 cm² | 0° | 10 mW/cm² | Small source over a small sensor area. |
| 2 kW | 1 m² | 60° (cos applied) | 1000 W/m² | Cosine factor reduces irradiance by half. |
Examples assume the flux is evenly distributed over the stated area.
Radiant flux (Φ) tells you total optical power, while irradiance (E) tells you how strongly that power is delivered to a surface. Many engineering decisions depend on surface intensity, not total power: heating, curing, photochemistry, sensor saturation, and photovoltaic performance are all driven by power per unit area.
For a uniformly illuminated surface, the relationship is straightforward: E = Φ / A. Doubling the area halves the irradiance, and doubling the radiant flux doubles the irradiance. The calculator normalizes your inputs to watts and square meters, then converts the result into your selected output unit.
W/m² is common in radiometry and thermal analyses. Smaller footprints often use mW/cm², especially for lasers, LEDs, and UV processes. Very small detector spots can be described as W/mm². The included conversions help you match lab instruments and datasheets.
If the same beam hits a planar surface at an angle, the effective delivered intensity reduces. The optional cosine correction applies E · cos(θ) for incidence angle θ. For example, at 60° the cosine is 0.5, so irradiance becomes half of the normal-incidence value. This is useful for tilted panels and optical benches.
As a quick check, outdoor sunlight on a clear day can be roughly on the order of ~1000 W/m² near noon. Many indoor lighting conditions are far lower in radiometric terms. UV curing and photobiology systems are often specified in mW/cm², with exposure targets defined by irradiance multiplied by time.
The most common error is using the physical surface area rather than the illuminated area. If a beam only covers a small spot on a large plate, use the spot area. If illumination is non-uniform, consider an effective area based on the region that receives most of the power, or measure irradiance directly and compare.
Radiant flux is typically measured with integrating spheres or calibrated power meters, while irradiance can be measured with radiometers and detector heads that have a known active area. Report units clearly, include angle assumptions, and keep rounding consistent with instrument accuracy. This calculator lets you control decimals for clean documentation.
Use this calculator for optical source comparison, determining exposure dose planning, estimating heating on coatings, checking sensor limits, and converting datasheet power ratings into surface intensity. Exporting CSV or PDF helps you keep calculation records alongside experiment logs and design reviews.
Radiant flux is total optical power in watts. Irradiance is power per unit area, such as W/m² or mW/cm², describing how strongly a surface is illuminated.
Enable it when a planar receiving surface is tilted relative to the incoming beam. The correction multiplies irradiance by cos(θ), reducing intensity as incidence becomes more oblique.
Use the illuminated spot area, not the full target size. For circular spots, A = πr². For rectangular spots, A = width × height, using consistent units.
This usually indicates the entered area is too small, or units were mismatched (cm² vs m²). Recheck the illuminated area and confirm the selected area unit.
Yes, if Φ represents average radiant flux over time. For pulses, compute average power from pulse energy and repetition rate, then convert to irradiance using the same area.
They represent the same concept with different scaling. A convenient rule is 1 W/m² equals 0.1 mW/cm², which helps translate between lab and engineering conventions.
No. It converts geometric distribution of radiant power over area. If your surface reflects or absorbs, apply a separate factor (for example, absorptivity) to estimate absorbed irradiance.
Important Note: All the Calculators listed in this site are for educational purpose only and we do not guarentee the accuracy of results. Please do consult with other sources as well.