Poison ivy leaves show a bright yellow in sodium light while grass etc. is a dull green, so why?

Question

does this happen? I have a high pressure sodium yard light the kind that is yellow. I know the light comes as a very narrow part of the spectrum. I was mowing my lawn tonight as twilight darkened and in the back corner where I have some poison ivy, I found more than I expected because the leaves were glowing yellow in comparison to the greenery around that seemed a dull green. This will be handy when I go out with poison ivy killer tomorrow night and hit those spots, but why is it happening? Is it related to toxins in the oil? To something like carotine in the leaves?

Answer 1

Poison ivy secretes a chemical (which causes a rash on some peoples skin).  This chemical is not found on other plants, such as grass, etc..  This particular chemical absorbs/reflects  specific wavelengths of light when a sodium source is used to "light" it up.  It's all about reflection due to chemical in the poison ivy, of a specific wavelength (or frequency) of a light of known SINGLE wavelength (ie:  the sodium vapor lamp)  Got it?

Answer 2

The chemical in poison ivy is urushiol or urushiol induced contact dermatitis when exposed.  I like many people am very allergic to it. I found your observation helpful as when small plants invade the lawn they are nearly impossible to see. This could be a way of exposing them at night to keep the mower from running over the next day making them airborne. Thanks for your helpful observation and making it available.