Yet another post on measuring light bulbs. This post is on 'beam angle'.
Common terms in selecting a light bulb are 'flood' light or 'spot'
light. These are designations of beam angle. The beam angle is the
degree of width that light emanates from a light source. Specifically:
The angle between those points on opposite sides of the beam axis where
the intensity drops to 50% of maximum. This is shown graphically below:
Typically a narrow beam angle is a 'spot' of light and a broader beam
angle 'floods' an area with light, called a
flood light. There are a
number of much more specific designations of beam angle. They are not
used consistently between all the light bulb manufacturers. For
MR16
bulbs the following is generally used by Silvana, GE and Philips:
- VNSP: Very narrow spot - typically less than 7 degrees
- NSP: Narrow spot - typically from 7 to 15 degrees
- SP: Spot - typically from 16 to 20 degrees
- NFL: Narrow flood - typically from 21 to 30 degrees
- FL: Flood - typically from 31 to 40 degrees
- WFL: Wide flood - typically from 41 to 60 degrees
- VWFL: Very wide flood - typically greater than 60 degrees
The area lit is determined by the distance between the light source and
the subject. To light a larger area from a short distance a wider
(larger number of degrees) beam angle is used. To light the same area
from longer distance a narrower beam angle would be used.
A narrower beam angle will normally result in a greater brightness or
greater number of lumens for the same wattage: the light is concentrated
on a smaller area. This is typically done though optics via reflectors
or lenses.
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