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? (part 2)
In the previous discussion about lumens (https://physbang.com/2025/12/30/what-are-lumens/) some numbers were quoted without any explanation. This post adds a bit more detail to those numbers. Firstly, the maximum theoretical output of a light source was stated to be 683 lumens-per-watt. Why that number? The answer is to be found in the definition of the candela, which … Continue reading What are lumens? (part 2)
