"LAMP : What the un-initiated call a light bulb."
"The bulb is the decorative glass or plastic housing that diffuses the light distibution."
And for good measure;
LUMINOUS INTENSITY AND FLUX:
The unit of luminous intensity I is the candela (cd) also known as the international candle. The intensity of a light source is commonly referred to as its candlepower.
The unit of luminous flux F is the lumen (lm). One lumen is equal to the luminous flux which falls on each square meter (m2) of a sphere one meter (1m) in radius when a 1-candela isotropic light source (one that radiates equally in all directions) is at the center of the sphere. Since the area of a sphere of radius r is 4pr2, a sphere whose radius is 1m has 4pm2 of area, and the total luminous flux emitted by a 1-cd source is therefore 4p1m.
Thus the luminous flux emitted by an isotropic light source of intensity I is given by:
F = 4pI where
Luminous flux (lm) = 4p × luminous intensity (cd)
The illumination (or illuminance) E of a surface is the luminous flux per unit area that reaches the surface:
E = F/A Illumination = luminous flux / area
Luminous Intensity & Luminous Flux:
lumens = 4π × cd cd = lumens
lumens = 4π × (Mean Spherical Candlepower)
fc = cd cd = fc × d ²
lumens = fc 4π × d ² fc = lumens
4π × d²
Inverse Square Law: E = I
d² Cosine Law: E = I cos θ
where θ is angle of incidence d² d²
10.764 × fc = lux
1 lux = 0.0929 fc
10.764 × lumens / sq. ft = lux
lumens / m² = lux
1 cd / sq. ft. = π × fL (foot-Lambert)
3.426 × fL = nits = cd / m²
1 fL = 1 lumen / sq. ft.
1 fL = 3.426 cd / m²
1 cd = 1 lumen per steradian (unit solid angle), where “steradian” unit solid angle is a cone. Unit solid angle is photometric brightness, where the spherical surface is:
S = 4π²
If r = 1, then there are 4π lumens in the sphere, (12.566 lumens)
Source: Engineering Dept.
OK, OK, so the above has nothing to do with lamps, bulbs, or any combination of therin. But, it looked pretty offical like on the page I got it from.