Effect of altering incident light intensity on absorption

  • Thread starter madmazda86
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Hi all,

Physics was never my strong point at school, yet here I am looking at the differences between three types of graduated light filter for a Health Sciences Masters degree. I'm in the process of writing up, and one of my sets of results is a bit bewildering.

Basically, I measured the light absorption of these three filters (one of them's a graduated ND filter) using a strong light source and a weak light source. I was expecting the light absorption to be the same regardless of whether a strong or weak light source was used, because, well, the filters themselves haven't changed, they still block the same amount of light, it's just that the start and end points will be reduced because the light source is weaker. But no, using a weaker light source they block out more light at lower filter strengths compared to using a strong light source. I've used the same distance for all my measurements so it's not a change in that causing the difference. It's statistically significant so I need to come up with an explanation for this, and I am honestly stumped because everything I'm finding on the internet tells me what I suspected, that if incident light and transmitted light are proportionately reduced then absorption will be the same. Is it to do with there being more scatter with a weaker light source? Would be really grateful for some advice and even some journal article/website links if you have any!

Thanks :)
 

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