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[EnergyPlus_Support] Re: Luminous efficacy and fraction visible

Wouter: 

i do not think that the Lights object in the Internal Loads class takes into account the Luminous efficacy. The Fraction visible and Fraction Radiant fields in this object and the fconvected values shown in Table 13 of the V6 Input Output Documentation refers to the fraction of heat energy and not light energy 

The product of Solar Absorptance (SA), a property of the outer layer material of the wall construction, area of wall, Fraction visible and the Lighting Level (W) is the heat that is absorbed into the inside face of the wall. The product of Thermal Absorptance (TA), another property of the outer layer material of the wall construction, area of wall, Fraction Radiant and the Lighting Level (W) is another heat that is absorbed into the inside face of the wall due to the longwave radiations. These two heats are used in the surface heat balance calculations.  

Luminous efficacy, in EnergyPlus refers to those from the sun. i think these Beam and Diffuse lum/W are used in the Daylighting objects. 

ooi

Wouter wrote:

The InputOutputReference states that:

"Fraction Visible: The fraction of heat from lights that goes
into the zone as visible (short-wave) radiation. The program
calculates how much of this radiation is absorbed by the inside
surfaces of the zone according the area times solar absorptance
product of these surfaces."

How exactly does this relate to luminous efficacy of the applied
lighting system (and luminaire efficiency)?

If I take an T8 fluorescent tube with a luminous efficacy of 80
lm/W, then I would say that the fraction visible is about 12%
(80/683, where 683 lm/W is the number of lm/W of a hypothetical
monochromatic green light source that would have 100% of its
energy visible).

This is clearly less than the 18% that is given as a reference
value for fluorescent lighting in the table below the definition
of Fraction Visible. The second sentence of the definition
indicates that absorption of this radiation is calculated using
solar absorptance, implying that the spectral range of
the radiation is broader than the visible range. Does
this explain the higher value of 18%?



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