Basics
Photons
\[E = \frac{hc}{\lambda} = h\nu\]
Radiometry
Name |
Symbol |
Unit, Symbol |
|---|---|---|
Radiant energy |
\(Q_{e}\) |
joule, J |
Radiant flux |
\(\Phi_{e}\) |
watt, W |
Radiance |
\(L_{e}\) |
watt per steradian per square metre, W⋅sr -1 m -2 |
Irradiance |
\(E_{e}\) |
watt per square metre, Wm -2 |
Spectral irradiance |
\(E_{e,\lambda}\) |
watt per square metre per nanometre, Wm -2 nm -1 |
Spectral irradiance can equivalently be expressed as a function of light frequency, but it is much more common to use the wavelength.
Photometry
Name |
Symbol |
Unit, Symbol |
|---|---|---|
Luminous flux |
\(\Phi_{\small{V}}\) |
lumen, lm |
Luminance |
\(L_{\small{V}}\) |
candela per square metre, cd⋅m -2
or lumen per steradian per square metre,
lm⋅sr -1 m -2 |
Illuminance |
\(E_{\small{V}}\) |
lux, lx |
Exposure |
\(H_{\small{V}}\) |
lx⋅s |