Table 2.

Uncertainty budget for illuminance calibration

Source of uncertainty		Relative standard uncertainty (%)
		Type A	Type B
s(555)
	Spectral responsivity scale		0.11
	Comparison of photometer with scale	0.04
F
	Measurement scatter (noise)	0.01
	Data fitting procedure	0.01
	Residual non-uniformity within aperture	0.02
	Color temperature of lamp(± 10 K)		0.02
	Planckian approximation for lamp		0.02
	Infrared leakage		0.003
	Ultraviolet leakage and fluorescence		0.002
Correlated s(555) and F
	Wavelength calibration		0.04
	Numerical aperture		0.05
A
	Aperture area (as certified, small apertures)		0.05
Additional
	Temperature variation		0.03
	Polarization sensitivity		0.01
	Electrical current-to-voltage conversion	0.003
	Responsivity nonlinearity		0.001
	Other		0.12
Combined standard uncertainty		0.19
Expanded uncertainty (k = 2)		0.39