Re: Anyone moved to LED Lighting?

[don@xxxxxxxxxxxxxx (Don Klipstein)]

In article <hgvfmk$oea$2@xxxxxxxxxxxxxxxxxxxxxxxxxx>, Stormin Mormon wrote:

>If memory serves, a diffraction grating is a series of very
>tiny prisms, adding up to the effect of being a very large
>prism, but some how made flat.

  The principle is different.

  A prism refracts (bends) different wavelengths of light unequally.

  A diffraction grating works with diffraction - light hitting or grazing
small objects is bent or even reflected into random directions or a range
of random directions.
  The grating has a large number of equally-spaced grooves.  That causes
the light to go only where the various paths (one for each groove) have
distance from light source to destination differ from each other in length
by only whole numbers of wavelengths, so that constructive interference
occurs.

  The effect remains similar to that of a prism.  The biggest
functional differences between a prism and a diffraction grating are:

1.  It can be tricky or necessary to use additional optics to get a
well-spread-out spectrum of good quality.  A diffraction grating all by
itself easily produces a nice spectrum.

2.  With a prism, the violet end of the spectrum tends to get stretched
outand the red end tends to get squished.  Variation of refractive index
of transparent materials with change in wavelength tends to be greater at
shorter wavelengths than at longer wavelengths.

3.  Some gratings are of reflective type.  A CD or DVD is an example of a
reflective grating.

  Some "spindle packs" of recordable CDs or DVDs have a clear one at the
top and sometimes the clear one has the grooves - and that makes that
thing an example of a transmissive diffraction grating.

 - Don Klipstein (don@xxxxxxxxx)