Factory calibration procedures

LI-COR quantum sensors are calibrated using a standard light source calibrated against a National Institute of Standards and Technology (NIST) lamp. The photon flux density from the standardized lamp is known in terms of micromoles s^-1 m^-2 where one micromole = 6.022 × 10¹⁷ photons.

The uncertainty of the calibration is ± 5%. The lamp used in LI-COR's calibration is a high intensity standard of spectral irradiance (G.E. 1000 watt type DXW quartz halogen) supplied with a spectral irradiance table.

The following procedure is used to calculate the quantum flux output from the lamp. The lamp flux density (E) in watts m^-2, in an increment at a wavelength can be expressed as

2‑1ΔE = E(λ)Δλ

where E(λ) is the spectral irradiance of the lamp at wavelength λ.

The number of photons s^-1 m^-2 in Δλ is

2‑2

where h is Plank's constant and c is the velocity of light. This can be summed over the interval of 400-700 nanometers (nm) to give

2‑3

The result is adjusted to μmol s^-1 m^-2 by dividing by 6.022 × 10¹⁷.