Technical information

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Light planning
Quantities, units and their significance
Quantity/Concept Symbol Unit Formula Explanation
Luminous intensity Ι candela
(cd)
I=Φ/ω Luminous intensity is the intensity in a determined direction. Definition: Luminous flux per solid
angle (ω). Definition: Luminous flux per solid angel (ω)
Illuminance E
(lx)
Lux
(lm/m²)
Illuminance refers to the luminous flux that hits a specific surface.
Definition: Luminous flux per unit area (m²).
Luminance
(luminous intensity)
L (cd/m²) L=I/A
(L=I/Acosα)
This is defined as the luminous intensity in a specific direction from a surface of a
light source, luminaire or lit surface, divided by the projected area.
Luminous flux Φ lumen
(lm)
Φ=I/ω Luminous flux refers to the total amount of light emitted from a light source. It is defined as the
amount of light emitted when the light source’s radiant luminous flux, is evaluated against the eye’s
sensitivity in daylight (V
λ
-curve according to CIE).
Design lumen Φ
B
lumen Refers to the light source’s luminous flux that is emitted at an ambient temperature of 25 °C. The
quoted luminous flux may dier from the light source’s maximum luminous flux. (For example
T5-fluorescent lamp).
Light Output Ratio
(LOR)
η
A
Ratio between the total flux from the luminaire, measured under specified practical conditions with
its own light sources and equipment, and the total individual luminous flux from the same light
sources operating outside the luminaire using the same equipment, under specified conditions
Design eciency η
B
The design eciency of the luminaire is used in lighting calculations together with the design lu-
men for the light source. The design eciency includes the correction for BLF when measuring the
luminaire and light source in an ambient temperature of 25 °C. η
B
= η
measured
x BLF.
Ballast Lumen Factor BLF – – Defines the luminous flux from a light source. It is measured with either a commercial ballast or a
reference ballast, at an ambient temperature of 25 °C.
Colour temperature – kelvin (K) CIE 17.4 The colour temperature is dened using absolute temperature. (0 K = -273.15 °C or 0 °C = +273.15 K)
Colour reproduction index Ra Ra-index CIE 17.4 Is the measurement of a light source’s ability to reproduce colour compared to a reference light
source at a predetermined colour temperature. An Ra index is used for graduation, which according
to CIE, can be at the most 100 and shall for lighting workplaces be a minimum of 80.
Luminous ecacy – light
source
H (lm/W) η=Φ/P The luminous ecacy from a light source can be defined as the relationship between the luminous
flux emitted by a light source and the electrical output it consumes. Luminous ecacy can also be
described as a measurement of light source eciency.
Luminous ecacy – system
(light source + ballast)
H (lm/W) η=Φ/P The system luminous ecacy from a light source can be defined as the relationship between the lu-
minous flux emitted by a light source and the electrical output it consumes including ballast losses.
Glare CIE- 31,
112, 117
Is a visual impairment caused by the extreme contrast or inappropriate distribution of luminance
levels. Glare is normally subdivided into: -discomfort glare UGR/NB – disability glare TI/GR.
Uniformity
– illuminance
– luminance
E
min
/E
ave
L
min
/L
ave
Ratio between the lowest value and the average value of brightness on a specific surface unless
otherwise stated.
Luminaire luminance – – The average luminance of a luminaire’s luminous parts measured and/or calculated in the C-plane
at 15° intervals starting at 0°, and elevation angles (γ) of 65°, 75° and 85°.
Shielding angle for lumi-
naire’s light source
– – The angle between the horizontal plane and the first line of sight at which any part of the lumi-
naires light source becomes directly visible.
Cut-o angle for luminaires – – Angle, measured upwards from nadir, between the vertical axis and the first line of vision at which
the light sources and surfaces with high luminance are not visible.
Solid angle ω steradian
(sr)
ω=A/r² The relationship between the cut out area A on a sphere caused by a beam of light on its surface
and the square of the spheres radius r.
Mean mortality rate
– for light sources
– hour (h) – Mean mortality rate is the average life span of a light source and is defined as the time after which
50 % of a large number of controlled light sources have failed (Incandescent lamps, halogen lamps
and fluorescent lamps).
Service mortality rate
– for light sources
– hour (h) – The service mortality rate is dened as the point at which 80 % of the lighting installation’s original
luminous flux remains. The depreciation in luminous flux depends on the reduced luminous flux
and spent light sources.
Economic mortality rate
– for light sources
– hour (h) – The economic mortality rate is defined as the point at which 70 % of the lighting installation’s
original luminous flux remains. The depreciation in luminous flux depends on the reduced luminous
flux and spent light sources.
For standardised definitions and further clarification of magnitudes, units and concepts, see EN 12 665 – Basic terms and criteria for specifying lighting requirements. (EN 12 665 – Basic
terms and criteria for specifying lighting requirements).
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