### Description

Several different units are used to describe light, depending on whether it is eminating from a source, falling on an object, or being reflected from an object.

NOTE: Please check units for luminance before using in critical applications.

Light Parameter

Term

SI Unit

light source

light source

light incident on a surface

illuminance

lux

light reflected from a surface

luminance

lambert

(from Table 6.1, Miller and Sarmiento, 1999)

Light Source

Lumen (lm): The luminous flux through a unit-solid angle (steradian) from a uniform point source of one candle

(1) 1 lumen = 1 candela (cd) steradian = 1 candle

Illuminance

Lux (lx): 1 lumen per square meter

(1) 1 lumen per square meter = 1 meter-candle = 1 lux

(2) 1 lumen per square meter = 0.0929 foot-candle

Foot-candle:

(1) 1 foot-candle = 1 lumen per square foot = 10.76 meter-candle

Phot:

(1) 1 phot = 1 lumen per square centimeter

(2) 1 lumen per square meter = 0.0001076 lumen per square centimeter

Output

Input (below)

lm per sq meter

lm per sq cm

lm per sq foot

lm per sq meter

1

10^(-4)

0.0929

lm per sq cm

10^4

1

929

lm per sq foot

10.76 = 1/0.0929

1/929

1

Luminance

Lambert:

(1) 1 lambert = (1/π) * (1 candle per square centimeter) = 0.3183 candles per square centimeter

(2) 1 lambert = 3183 candles per square meter

(3) 1 lambert = 295.4 candles per square foot

(4) 1 lambert = 2.05 candles per square inch

Foot-lambert:

(1) 1 foot-lambert is the luminance of a perfectly diffusing and reflecting surface illuminated by 1 candle at a distance of 1 foot.

(2) 1 foot-lambert = 0.3183 candles per square foot

(3) 1 foot-lambert = 0.00221 candles per square inch

(4) 1 foot-lambert = 0.0003426 candles per square centimeter

(5) 1 foot-lambert = 0.001076 lamberts

(6) 1 foot-lambert = 3.425 candles per square meter

where:

• 1 meter = 3.28 feet; 1 square meter = 10.76 square feet; 1 / (square meter) = 0.0929 / (square feet)

• 1 square meter = 10^4 square centimeters

• 0.3183 = 1 / π

• 0.2919 = 1/ (3.426)

• 1 square foot = 144 square inches

• 1 square inch = 6.45 square centimeters

Output

Input (below)

lambert

foot lambert

candle per sq inch

lambert

1

1/(0.001076)

2.05

foot lambert

0.001076

1

0.00221

candle per sq inch

1 / 2.05

1 / (0.00221)

1