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Irradiance is the amount of energy emitted at each wavelength from a radiant sample such as an LED, a laser or the sun. From that data, more specific intensity values can be calculated.
Relative irradiance uses a lamp with a known color temperature to correct the shape of the spectrum but not its magnitude. Relative irradiance can determine whether there is more power at one wavelength than another, but not how much power there is in absolute terms.
Absolute spectral irradiance requires a lamp of known spectral power output to calibrate the spectrometer’s response at each pixel. This modifies the shape and magnitude of the spectrum, correcting for the instrument’s response function. The modified spectrum is given in terms of power per area per wavelength.
In this tutorial, we guide you through the steps to take when measuring the absolute irradiance of sources including lamps and LEDs. Learn how to calculate power output at each wavelength.
A modular setup for measuring LEDs comprises a spectrometer like our Flame, Ocean FX or Ocean HDX models, plus optical fibers and an integrating sphere to collect the output from the LED. Also, we can add an LED power supply/controller to operate the LED and adjust its drive current, and for absolute irradiance, include a radiometrically calibrated VIS-NIR source designed for use with an integrating sphere.