Colored LED's and penetration through skin and flesh

[alanagnostic]

I have several lights with colored LED's and for fun I held them up to my hand and I noticed that the light from my red LED's went right through my fingers and even part of my hand. It was actually kind of cool to see blood vessels and bones. But I noticed that the green and blue LED's hardly went through my hand at all.

My guess is that the long wavelength of red light will simply pass more easily through skin and flesh. Does anyone know if this is correct? If that is all there is to it then I don't understand why X rays are used to see through our bodies when I thought they were short-waved radiation.:candle: Does anyone know?

 

[defloyd77]

Your skin basically acts as a red filter. Blue and green lights emmit no red light, therefore you won't see anything, white lights shine somewhat through because of some red light, red leds, well are red and won't be "filtered" that much. Hope that makes sense. If you have any colored filters or anything else clear colored try all of the different color combinations to further example this theory.

 

[alanagnostic]

defloyed77, thanks for the response but I guess I don't get it. It seems like my hand is acting like a blue and green filter....it's letting through the red but not the green or blue. My main question is why is the red light going through and not the green or blue. I think it must have something to do with the wavelength of the different colors but I'm not sure.

 

[luigi]

Objects are seen of a given color because the material reflects that color and tends to absorb the others. Human tissue tends to be red, muscles, blood, etc.
So my guess is that tissues tend to reflect red and absorb blue and green light when you point a red light thru your hand the reflected red light is what illuminates your hand. With blue and green light is absorbed by tissues and the illumination effect is less noticeable.

Luigi

 

[defloyd77]

I meant a red colored filter, that turns white light red.

 

[PhotonWrangler]

Your skin acts as a red bandpass filter. Conversely it's a bandstop filter for the shorter wavelengths at the green-blue end of the spectrum.

 

[IsaacHayes]

Yup and those that don't go through you can feel sometimes as heat on your skin if the light is powerful l enough. I'm not talking about the IR heat you feel from an incandescent, but the wattage from say a strong blue power led focused on your hand. You skin is absorbing the energy.