Popular Science/Light



I was doing a pH experiment for class using cabbage, and had one item (baking soda + water) in a small cup turn blue. It was blue under fluorescent kitchen lights, but I noticed it was purple under regular incandescent. The change in colors seemed very distinct. Can you tell me why the lighting produced different colors?


Hi KC,
Any substance being struck with light (photons of different wavelengths) there are only three things it can do:
1. transmit the photons through the substance.  (called "transparency")
2. absorb the photons.
3. and/or reflect the photons.
There are no other options allowed.
What we call "color" is simply the photons of a certain wavelength being reflected, and our eye and brain interprets that wavelength(s) as "color".
If all wavelengths of the visible light spectrum are reflected, then we call the object white.
If all wavelengths are absorbed and none are reflected, then we call the object black.
If only the wavelength of say, 5007 Angstroms is reflected, then we call the object blue-green, and so on.  Obviously if the incoming light is modified, then the substance must react differently to those different incoming wavelengths (incandescent which is more yellow light, vs. fluorescent light)...  and that's probably why you see a different color change.
I would imagine that if you shine UV light (or what we call black light)on it... (or a green laser pointer light)...  you'd get still a different color being reflected by the solution.
Hope this helps,
Clear Skies,
Tom Whiting
Erie, PA  

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Tom Whiting


I can answer most questions involving general science and engineering, except those involving electronics and computers.  My strong points are all the Earth Sciences, especially Meteorology and Astronomy, and any related subjects to Astronomy.  My weak point is Electronics Technology.   No astrology questions please, or questions about alleged UFO identifications.


My hobby has been Astronomy for over 50 years. I currently ownand use a 30 inch portable telescope.   I taught at the University Level for 13 years.  My personal interest in life, in general,  has always been science oriented.

President - Erie County Mobile Observers Group for over 15 years.Member of allexperts.com astronomy catagory for over 8 years.

Astronomy Technology TodayErie Times Newspaper - I wrote the "Over Erie Skies" columnfor 11 years.

BS  Metallurgical Engineering Grove City College, PAMaster's Degree, Gannon University, Erie, PAAlso retired USAF pilot, 20 years.

Awards and Honors
I was the discoverer of the Mini-Coathanger Asterism up in Ursa Minor.  I earned 6 Air Medals with USAF and retired after 20 years of service with the rank of Major, with over 2100 hours flying time.I also earned the rank of Eagle Scout in 1956.

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