DeltaOHM HD2402, Руководство по эксплуатации

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HD2402
- 9 -
V1.4
2.2 R
ADIANCE
Radiance L
i
at a point of a surface is defined as the energetic flux d
2
Φ
I
that flows
through a surface dA per unit solid angle d Ω (Figure 2):
Ω ⋅
Φ
=
d dA
d
L
i
2
Figure 2: radiance
The radiance measurement unit is [W/(m
2
sr)]; when calculated at different wave-
lengths, we obtain the spectral radiance [W/(m
2
nm sr)].
A solid angle is the angle subtended at a point P by a closed surface A . It is calculated
as the relation between the surface projected on a sphere of radius R with center in P
and R
2
. The measurement unit of a solid angle is the steradian [sr] and its value
ranges between 0 and 4 π .
Radiance and irradiance are two different quantities. Radiance describes the angular
distribution of radiation while irradiance integrates radiance in all directions. The pri-
mary relation linking irradiance to radiance is:
( )
ω θ φ θ
d L E
i i
) cos( ,
∫
Ω
⋅ =
If radiance is uniform, then the term L( θ , φ ) can be taken out from the integral and the
expression is simplified as follows:
F L d E
i
i
i
L
⋅ = =
∫
Ω
ω θ
) cos(
Where F depends only on geometry.
In these particular conditions, the radiance value can be obtained from that of the ir-
radiance: hence, the formula will be:
F
E
L i
i
=
Remark : for small angles, F is actually the solid angle under which the observer
source is seen.
By using this reduction, HD2402 unit allows to calculate the radiance of the irradiance
measured values.