Does Combining Lumens Make a Difference?

  • Context: High School 
  • Thread starter Thread starter mattloto
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Discussion Overview

The discussion revolves around the behavior of lumens when combining multiple light sources, specifically whether two light bulbs producing 1,000 lumens each result in the same brightness as one bulb producing 2,000 lumens. Additionally, participants explore how to measure brightness when a lens is placed between a light source and a wall.

Discussion Character

  • Exploratory, Technical explanation, Debate/contested

Main Points Raised

  • One participant questions if two 1,000 lumen bulbs combined produce the same effect as one 2,000 lumen bulb.
  • Another participant asserts that the lumens do add together.
  • A third participant emphasizes the importance of understanding the units of visible radiation and suggests that proper definitions are crucial for accurate communication.
  • One participant explains that while lumens are a photometric measure of radiant flux, the addition of lumens is contingent upon the spectral output of the light sources being identical.

Areas of Agreement / Disagreement

There is no consensus on the question of whether lumens from multiple sources combine in the same way as a single source. Some participants agree that they do add, while others highlight the complexity involved in the conversion and measurement of lumens.

Contextual Notes

Participants note that the spectral sensitivity of vision affects the conversion from watts to lumens, indicating that not all light sources with the same wattage will produce the same lumen output.

mattloto
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I've looked for this answer around the web, and I've gotten mixed results, so I'm asking here. If I have 2 light bulbs that produce 1k lumens each, will it be the same as 1 light bulb producing 2k lumens?

And on the topic, if I have a light source and I put a lens between it and a wall, what measurement will tell me how bright the image will be when it hits the wall. Thanks!
 
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I believe that they do add with each other.
 
mattloto, get yourself educated in the units of visible radiation. Actually, there are a lot of them, some derived, like the lumen. Once you have the definitions down correctly you can always communicate with others accurately. You might start here:
http://en.wikipedia.org/wiki/Lumen_(unit )
 
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Lumens are a photometric version of radiant flux, the radiometric units are Watts. Because flux (power) is an integrated quantity, it does not have any directional dependence. So yes, the lumens will add.

However, because 'lumens' takes into account the spectral sensitivity of vision, you have to be careful when converting watts to lumens- two identical wattage bulbs, if the spectral output is different, will have different lumens.
 

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