Calculations

LIGHT BEAM CALCULATIONS

Beam diameter = distance * (2 * tan (beam angle / 2))

Throw distance = Square root ((horizontal dist. * horizontal dist.) + (vertical dist. * vertical dist.))

LIGHT OUTPUT CALCULATIONS

1 candela = 12.57 Lumens

Foot-candles = candela / distance in feet * distance in feet

Foot-candles * 10.764 = Lumens/sq meter

1 Lumen/sq meter = 1 Lux

Lumens/sq ft * 1 = foot-candles

Lumens/sq ft * 10.764 = lumens/sq meter

Lumens * 0.07958 = spherical candle power

Lambert * 0.3183 = candles/sq cm

Lambert * 295.720 = candles sq ft

Lambert * 1 = lumens/sq cm

Lumens/sq. ft. * 1 = foot-candles

Lumens/sq. ft. * 10.764 = lumens/sq meter

Lumens * 0.07958 = spherical candle power

Lux = candela / distance in meters * distance in meters

Lux * 0.0929 = foot-candles

LUMINAIRES EFFICIENCY RATING - LER

EFF = luminaire efficiency

TLL = total number of lamps per luminaire X rated lumens per lamp

BF= ballast factor

IW = Input Watts, the total system watts of the luminaire

LER = EFF X TLL x BF / IW

POWER CALCULATIONS

Power = Voltage * current (Watts = Volts * Amps)

Current = Power / Voltage (Amps = Watts / Volts)

RMS Volts = 0.707 * Peak Volts RMS Volts = 1.11 * Average Volts

ROOM CAVITY RATIO

RCR = 5 * H * (L+W) / (L * W)

RCR = 2.5 * Total Wall Area / Floor Area

H = height

L = length

W = width of the room

A cubical room will have an RCR of 10, the flatter the room the lower the RCR.

SPACING TO MOUNTING HEIGHT RATIO

Sp = Spacing between Lights

MH = Mounting Height above Work Area (living room floor, or kitchen countertop)

WH = Wall Height

DfW = Distance from Wall

DtO = Distance to Object

Recessed Downlighting with Incandescent Flood Light Bulbs

Sp = 3/4 * MH to a maximum of 1 * MH

Recessed Downlighting with Halogen Flood Lights

Sp = 1/2 * MH to a maximum of 3/4 * MH

Wallwashing with Recessed, Track, or Landscaping Lights

Sp = 1/4 * WH,

DfW = 1/4 * WH, and

Aim 1/4 down the wall, or up the wall in the case of landscape lights

Grazing with Recessed, Track, or Landscaping Lights

Sp = 12 - 18",

DfW = 6 - 12"

Highlighting Paintings with Recessed, or Track Lights

DfW = 2/3 * DtO

Highlighting Three Dimensional Pieces with Recessed, Track, or Landscaping Lights

DfW = 2/3 * DtO

Sp = 12 - 18"

VOLTAGE DROP OF CONDUCTOR - LENGTH CALCULATION

V = voltage drop,

I = current

L = length of conductor in feet

R = resistance of conductor per 1000 feet

R for 18awg = 6.51, 16awg = 4.09, 14awg = 2.58, 12awg = 1.62, 10awg = 1.02, 8awg = 0.64

V = I * L * (R / 1000) * 1.004