“When examining the typical LED profiles, observe that the space above the curve inside and the space below the curve outside of the 50% points are similar.”
E is exposure in joules per cm² (J/cm²); Ip is peak irradiance under the lamp head in watts per cm² (W/cm²) at a specific distance; D is the distance (in the travel direction) between the 50% irradiance points, in inches (or mm) [This is approximately the width of the LED array and may be similar to, but smaller than, the window dimension]; and v is the velocity of the surface under the lamp, in inches per second (or mm/s). This method gives a good approximation of the exposure under an LED, or several LEDs, when a dosimeter or an integrating radiometer is not practical or available. n
the “tails” make it difficult to calculate exposure (Figure 2). To find the area under the curve, which is proportional to exposure, we are usually forced to use an integrating radiometer. LEDs are arrays of packed LED dies, so they usually have a characteristically “soft” irradiance profile. Profiles will be similar, even if the array has some concentrating optics applied. When examining the typical LED profiles, observe that the space above the curve inside and the space below the curve outside of the 50% points are similar – they have similar areas. This leads to a very rough approximation: E = Ip x D/v
R.W. Stowe
Director of Applications Engineering Heraeus Noblelight America LLC dick.stowe@heraeus.com
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UV+EB Technology • Issue 2, 2016 | 11