Lpw
Lpw
"Is anyone able to explain to me how to"
This is a real challenge due to the two different Surface Illuminance methods and Mfr luminaire cut-sheets needed to determine a reflective cavity or workplane surface for a required minimum footcandle (Fc) intensity. (I.e. Lux meter reading.)
Illuminance levels vary by task or mood lighting source distances and comprise a wide color spectrum from 'warm' incandescent to halide 'cool' illuminations that are also replicated by phosphor coatings in fluorescent tubing. (LED technology also has advanced with limited spectral color that almost match warm and cool color temp ranges.)
Photometric charts are needed to define each manufacturer's luminaire type for diffused or direct lighting reflective efficiency from the lamp output efficacy that is usually stated in rated lumens per watt.
Diffused (zonal) lighting is a radiated lighting source commonly found in fluorescent and frosted incandescent lamps.
Direct (point) lighting is a concentrated or focused lighting such as the IR Halogen MR16 and PAR lamps with narrow beam angles. LED's fall into the same narrow usually 10- 40 deg beam angles for distance effective illuminance.
So the challenge to illuminate a historic building depends on the lighting needed to replicate a mood of the era with upgrades that also comply to the minimum lighting codes required. A good start with what is acceptable with the planning board is the best bet before consulting with a lighting design subcontractor.
on my first visit I'll never know..... there they were plain as day, and I looked!!.