The second.
I see the "second" as a measure of time, not light.
LUX, Lumen or Candela do ring a bell and something like watt per square meter
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Yes the S.I. unit measure of light is a limen (lm) .
lumen (lm)
The SI derived unit for measuring the luminous flux of light being produced by a light source or received by a surface. The luminous intensity of a light source is measured in candela. One lumen represents the total flux of light emitted, equal to the intensity in candela multiplied by the solid angle in steradians (1/(4pi) of a sphere) into which the light is emitted. Thus the total flux of a one-candela light, if the light is emitted uniformly in all directions, is 4pi lumen.
Meters per second
Light-Years
Light years
(LY) Light Years and (AU) Astronomical Unit.
Agram is a submultiple of thekilogram, which is the SI base unit of measurement formass.The SI unit for weight is the newton.
. . they are a convenient unit. Another convenient unit is the parsec.
light years
The metre.
The meter is used to measure length.
The base unit for time is the second.
MassHowever, if, by 'primary unit', you mean 'base unit', then this is the kilogram not the gram.
Sunlight is light.The word has been added as the light comes from the sun.Light is measure in candela as a unit ofmeasurement.A Lux meter is used to measure light in the unit of candela.
The SI unit is meter. But nanometer and angstrom are commonly used units to measure the wavelength of light.
pH value(not the 'unit' just the scale)
Light-Years
Light years: the distance that light travels in a year.
Light years
(LY) Light Years and (AU) Astronomical Unit.