Light
Background Information
Light units
Lumens is the total light that a bulb produces in all directions.
Lux is the Lumens that fall onto a particular area.
PAR is the Lux measured between wavelengths 400-700nm ( blue-red spectrum most used by plants).
Daily light integral is PAR integrated over the course of a day.
Sidenotes
These are simplified definitions.
Lumens is a weighted function centered around 550nm (green spectrum most visible by humans). Phone apps estimate this value using camera exposure (aperature and shutter speed).
PAR is evenly weighted across 400-700nm ( violet-red ). Newer PAR meters no longer cut off below 450nm or above 650nm.
However due to these wavelength differences any conversion between Lux and PAR can be off by orders of magnitude.
Sunlight is distributed evenly and the conversion is consistent. PAR = Lux*0.0185
Fluorescent lights have spikes at multiple wavelengths and the conversion is inconsistent: PAR = Lux*0.0135
LEDs are highly dependent on color and have the most inconsistent conversions. Blue LED: PAR = Lux*0.0222
Light levels
Full sun
Noon sun: 100,000 Lux = 2,000 PAR
Direct sunlight all day: 50 DLI
Partial sun:
Morning sun: 50,000 Lux = 1,000 PAR
Direct sunlight in the morning and afternoon, dappled sunlight during noon: 20 DLI
Dappled sun
Filtered sun: 20,000 Lux = 400 PAR
Filtered sunlight all day: 10 DLI
Shade
Indirect sun: 10,000 Lux = 200 PAR
Indirect sunlight all day: 5 DLI
Inside a well lit room
Well lit room: 1,000 Lux = 14 PAR
18 hours of 14 PAR: 0.8 DLI
Species Info
Full sun: 30-60 DLI
Pinus thunbergii (Pine)
Juniperus chinensis (Juniper)
Punica granatum (Pomegranate)
Partial sun: 20-30 DLI
Acer palmatum (Maple)
Prunus serrulata (Cherry Blosson)
Rhododendron indicum (Azalea)
Dappled sun: 10-20 DLI
Certain trees like Ficus will thrive above 30 DLI and lose leaves to survive below 20. Just because a tree is alive doesn't mean it's healthy.
Calculator
Method
Sun calculations use sun angle (altitude and azimuth), sun intensity, and atmosphere conditions.
Indoor calculations take into account window angle and building obstruction.
Bulb calculations assume 18 hours/day at a constant level. PAR measurements done with a full spectrum meter.
Notes
A sunlight to PAR conversion factor of Lux / 54 is used.
Incident surface angle is modeled as a "leaf" which will turn towards ideal light throughout the day.
References
Inspiration
Korczynski, P.M.; J. Logan; J.E. Faust (2002). "Mapping monthly distribution of daily light integrals across the contiguous United States". HortTechnology12:12−16.
http://horttech.ashspublications.org/content/12/1/12.full.pdfBackground Information
Light Units
Sidenotes
Riddle, Dana (February 2013). "Aquarium Equipment: PAR Meters and LEDs - How Accurate are the Measurements? A Comparison of Three Meters and Lux to PAR Conversion Factors for LEDs". Advanced Aquarist.
http://www.advancedaquarist.com/2013/2/equipmentLight Levels
Light levels for growing orchids
http://www.orchidsusa.com/3Lightlevels.htmSun, Partial Sun / Partial Shade, Dappled Sun, Full Shade
http://gardeningwithconfidence.com/blog/2013/04/25/sun-part-sun-shade-part-shade/Species Info
Torres, Ariana P.;Lopez, Roberto G. (2010). "Measuring Daily Light Integral in a Greenhouse". Purdue Extension,HO-238-W,pp.5-7
https://www.extension.purdue.edu/extmedia/ho/ho-238-w.pdfEvergreen Tree Species Guide
Ford, John; Ticknor, Robert L. (1983). "Evergreen Trees and how to use them in your garden". Golden Press,pp.60-62
Bonsai Empire tree species guide
http://www.bonsaiempire.com/tree-speciesbonsai4me tree species guide
http://www.bonsai4me.com/species_guide.htmlCalculator
Sun Angle
Sun angle provided by the SunCalc.net project
https://github.com/mourner/suncalcTested against US Navy Observatory azimuth and altitude calculator
http://aa.usno.navy.mil/data/docs/AltAz.phpSun Intensity
Hourly sun intensity data from the National Solar Radiation Database provided by National Renewable Energy Laboratory
http://rredc.nrel.gov/solar/old_data/nsrdb/1961-1990/hourly/Amosphere conditions
Daily weather condition data from the National Solar Radiation Database provided by National Renewable Energy Laboratory
http://rredc.nrel.gov/solar/old_data/nsrdb/1961-1990/dsf/Losses due to atmosphere scattering
Losses calculated with equations and coefficients from Perez et al.
Perez,R.; Ineichen,P.; Seals,R.; Michalsky,J.; Stewart,R. (1990). "Modeling Daylight Availability and Irradiance Components from Direct and Global Irradiance".Solar Energy,44(5),pp.271-289.
http://www.physics.arizona.edu/~cronin/Solar/References/Shade%20effects/sdarticle%20(24).pdfIncidence angle equation
Light angles calculated with 3D incidence angle equation from PVWatts Version 1 Technical Reference (2013) published by the National Renewable Energy Laboratory.
http://www.nrel.gov/docs/fy14osti/60272.pdfTested against incidence angle from National Renewable Energy Laboratory's Measurement and Instrumentation Data Center Solar Position Calculator.
https://www.nrel.gov/midc/solpos/spa.htmlDirect beam radiation, sky radiation, and ground reflected radiation
Calculations follow the outline provided by Solar Radiation Data Manual for Buildings
http://rredc.nrel.gov/solar/pubs/bluebook/appendix.htmlTested against Monthly Solar Radiation and Illuminance for North, South, East, West, and Horizontal surfaces.
http://rredc.nrel.gov/solar/old_data/nsrdb/1961-1990/bluebook/state.htmlArtificial light data
Measurements taken with an Apogee handheld PAR meter.
PAR testing procedure explained.
https://www.youtube.com/watch?v=F-8OY0QBgrs