# Black light

1. Jul 7, 2012

### philrainey

if a wave of light intermingles with another the same but of opposite phrase I believe you get what is called black light. If the black light hits a blackbody what happens? does any radiation energy heat up the black body?

2. Jul 7, 2012

### DaveC426913

No. Black light is merely a common name for ultraviolet light.

http://en.wikipedia.org/wiki/Black_light

Ultraviolet light is simply shorter wavelength than violet light. Humans can't see it, though some other creatures (such as bees) can.

3. Jul 7, 2012

### philrainey

Oh I had this hairy fairy idea (thinking of light as waves) That two waves of opposite phrase travelling in the same vector kind of cancelled each other out. Maybe like add to zero. I thought as the universe is suppose to add to zero if the opposite of something is added to something then that something would return to zero. Then I went on with my notion and thought maybe that could be reversiable and one could in theory create light energy from nothing. Never mind.

4. Jul 9, 2012

### Q-reeus

philrainey wrote in:
#1:
#3:
philrainey - please carefully consider which sectioin in PF your queries truly belong. Both this one and previous one 'Bending radiation' are not really QM but more of a classical/general physics nature.

Wave interference is real enough but is believed to always obey total conservation of energy. Some examples are the light and dark interference fringes seen in double-slit experiments (classical optics or QM), or scattering of waves at waveguide junctions and obstacles, see e.g. http://en.wikipedia.org/wiki/Interference_(wave_propagation). The basic idea is such scattering/interference is 'unitary' - net input = net output. Which means cancellation in some regions is accompanied by reinforcement elsewhere and/or at other times ('beat' phenomena). One doesn't think of wave interference in terms of individual field quanta (photons) cancelling each other, but is really a collective phenomenon that emerges from the summed behaviour of many individual quanta.

Last edited: Jul 9, 2012
5. Jul 11, 2012

### philrainey

for years I thought black light was light waves that cancelled each other out, I really got it wrong. I think somebody at college told me that and I have believed it ever since. Well we have sorted that false notion out.