It is reasonable to expect a lamp’s apparent brightness to decrease with increasing distance from the source but what is the best way to determine the nature of the variation? Although there’s a theoretical answer that applies to all electromagnetic waves, based on the inverse-square law, it is important to be able to carry out … Continue reading Variation of Apparent Brightness with Distance
What are lumens?
Modern light sources are rated in lumens or, more importantly, lumens per watt. The first figure expresses the brightness of the source whereas the second indicates its efficiency. But what, exactly, is a lumen? To answer that question it is useful to recall that the first man-made light sources relied on heat and were very … Continue reading What are lumens?
