Photometrie new style: photonmetry

Radiation
In this website radiation always means electromagnetic radiation.
(The sun and stars also give particle radiation.)

In succession we consider radiation
at the source,
on the go and
when it hits a surface.

The conventional photometry
The traditional photometry contains some weird units.
The basic unit is candela of luminous intensity.
This is totally unnecessary,
being a source of a computable power.

Let us imagine candela is replaced by watt
then the lumen the unit of luminous flux
should be replaced by W/m2.

The unit of illuminance, the lux being lumen/m2
should be replaced by W/m4.

I define a completely new photometry
the photonmetry, in which all photometric units and
variables are derivated from power in watt.
Please ignore all the 'old' definitions in photometry.

The source of radiation

Power
Each radiation source emits an amount of radiation every second,
a number of photons. That is its source radiation power, P = {P} watt.
{P} represents a value for the number of watts.

Intensity
The radiated power per unit area is called the source intensity = I = {I} W/m2.

The source photon activity is the number of photons
emitted each second by a source. It is f = {f} Bq. (bq = becquerel)

The source photon intensity is the source activity per source area
So i = {i} Bq/m2.

Observability
The limits of the observable frequence ranges are different
for people, animals and artificial sensors
due to the sensitivities of the retina or the sensor.
For this reason ranges of frequencie are defined.

As a reminder:
The wavenumber of a wave is the number of wavelength in a meter

The visible range is defined as the range
from exactly 1.40 × 10⁶ m^-1 (red-IR)
until exactly 2.50 × 10⁶ m^-1 (violet-UV).
So the width of the range is exactly 1.10 × 10⁶ m^-1

The source light power is P_light.

It is the part of the power emitted as light.
The source light intensity is the source light power per area: I_light = {I_light} W/m2.
The source light photon activity is the number of light photons
emitted every time unit. f_light = {f_light} Bq

The source light photon intensity is the number of light photons
emitted every time unit per area of the source: i_light = {i_light} Bq/m2.

Other ranges of radiation
It is allowed to define any range of wavenumbers.
Wavenummers can be exchanged by frequencies.
Show the index UV or IR or ... .
Always mention the borders of the range.

On the go

When the radiation has left the source
there will be a radiation current or radiaton flux.
Its speed is c, the speed of light.

At any place in the flux there is an 'on the go radiation intensity',
shortly radiation intensity I = {II} W/m2.

The source radiation intensity is the initial case of the on the go intensity.
When later the radiation hits a surface
the hit intensity is the end value of the on the go intensity
That will be discussed later.

Selective absorption, refraction and dispersion
In any direction during on the go the radiation intensity always decreases
due to absorption, dispersion and due to 1/d ².
The environmental medium does it selectively
in respect to the (generalized) colours of the radiation.
Not only the colour intensity decreases
but as well the ratio of the intensity of the colours changes.

A hit surface

Hit quantities
A surface is hit by 'hit radiation'.
A surface can intercept a part of a beam and catches the hit radiation power.
The hit power of the radiation per area is the hit intensity.
It works the same way as at the source and on the go.

The hit radiation can be reflected partly and absorbed partly.
We do not pay attention to absorbtion nor to refraction.
When it concerns light we talk about hit light power and hit light intensity.

The brightness of a light souce equals hit radiation intensity by definition.
It is observerved by an eye or by a sensor as a fotoelectric cell.
(Again) I = {I} W/m2 for any colour range.
Always the hit intensity is less than the source intensity
Even with a laser.

A secundary radiation source
An object not being a light source can be seen
thanks to it reflects light to the eyes or sensor.
That is the way a surface becomes a secundary radiation source.
(For example the moon.)

The reflected generalised colour intensity in the direction of the observer
divided by the hit intensity for that colour in that direction
is the reflection factor between 0 and 1.
In astronomy the fractional reflected light intensity has been called the albedo.
The intensities of secundary radiation sources have been defined as with real ones.

Fractional quantities
The fractional source light power is the source light power divided
by the total source radiation power.
In the same way, all kinds of other fractional quantities
can be defined. All they are real numbers from zero to one.
Fractional quantities are denoted by the variable symbol
to which the slash is added as an index.
In that way exist
fractional source, on the go and hit light power P_light/
fractional source, on the go and hit light intensity I_light/
fractionele light brightness I_light/
fractional source, on the go and hit light photon activity f_light/ and
fractional source, on the go and hit light photon intensity i_light/
Light/ can be changed into UV/, IR/ or any generalised colour/. Mention the borders.

The fractional source light power of a lamp is the light yield.
The quality of an artificial light source is given by means of
the relative light output or its efficiency.

The units
From the previous sections we see candela, lumen, lux and stilb are not necessary.

We see the redundancy of the base dimension brightness
with the base unit the candela.

W/m2 is enough.

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