Measuring Energy Output
Hi How can I measure the total joules, per minute, from an
led floodlight bulb? I realize it changes as the distance grows.
Would a regular light meter help with this?
It is Joules per minute per square-meter that changes, not Joules per
minute. The Watt rating of the bulb is the Joules per SECOND. Divide
this by the area at a specific distance over which the light falls. For
a standard light bulb, the light is emitted in a spherical pattern:
divide by 4(pi)(radius^2). If the floodlight emits in only one
direction, you will have to estimate what portion of the spherical
surface is involved. A light meter usually measures such a quantity.
As color and light reflected from walls can affect what a light meter
reads, the meter only provides an estimate. Of course, the calculation
is also an estimate.
Dr. Ken Mellendorf
Illinois Central College
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Update: June 2012