Measuring Energy Output ```Name: John Status: student Age: N/A Location: N/A Country: N/A Date: N/A ``` Question: 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? Replies: John, 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 Physics Instructor Illinois Central College Click here to return to the Physics Archives

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