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Introduction
7
Lumens vs Watts
Watts will only tell you how much power the light consumes, not how much light it generates. Lumens will tell you what you actually need to know, how
much light you will get from a light source; and it is an easier means for comparing the amount of light you will get from one lamp versus another.
*
DIM stands for Domestic Implementing Measures.
Non-Directional Lamps
In non-directional lamps, the amount of lumens defines the total
amount of light the lamp generates irrespective of direction.
Directional Lamps
Previously, directional lamps only stated the luminous
intensity (candela) of the light. This would only indicate how
intense the light was and gave no frame of reference for the
quantity (lumens) of light.
The new DIM
*
2 legislation specifies that the amount of
useful light is the light that is emitted in a 90 degree cone
from the lamp. Any light outside this cone is not considered
useful in the pursuit of directional lighting.
It is however important to maintain an element of “spill
light”, that is light outside the cone to ensure homogenous,
uniform lighting.
Directional lamp lumens are defined by the amount of
useful light which is emitted forwards.
Useful lumens in directional lamps
The new legislation specifies that a 90º cone is used for the calculation of
reflector lumen output. This is because Halogen lamps have more spill light. To
accurately compare light emitted in a specific direction, we can only use the
lumens in a 90º cone. This is known as useful lumens.
GU10 5.5W LED 40º
90° Cone
300lm
600cd
Light spill
345lm
600cd
Light spill
GU10 Halogen 50W 36º
“Useful lumens” as measured within a 90º cone