US563836 A was granted in 1896. Edison's light bulb dates from 1879, US223898 A.

There is a key idea, namely a parabolic reflector made of glass. Rather than being silvered to reflect light, the parabolic bowl is made with prismatic fluting (triangular ridges) on the outside. Light entering through the smooth inside of the bowl is reflected twice inside one of the prisms, by total internal reflection. Total internal reflection is efficient, and if a little light leaks out it makes the exterior sparkly, rather than totally dark. I think I have seen such reflectors in life.

Years ago I visited the patent office and saw a patent on a simple parabolic reflector as just described. This 1896 patent, US563836 A, seems to be a more complicated version of the idea, presumably invented after the simple version.

As I sit searching on Google Patents, I get the feeling that the simpler patent is not in the Google system, or all the good keywords were garbled by OCR. Does anybody know the simpler parabolic-prismatic reflector patent, from about 1888?? Thank you. I have really struggled with this. My goal is to document a fascinating bit of history.

1 Answer 1


I found a method of making a hollow glass reflector from 1875

US362415A 1887-05-03 GLASS REFLECTOR.

and a housing for an electric bulb with triangular prismatic curved diffuser. US453187A 1891-06-02 HOBBS. GLASS GLOBE FOR ILLUMINATING PURPOSES.

In Google patent advanced or other sophisticated search sites you can avoid OCR issues by using classifications. A google advanced patent search using uspclass:"362/334" restricted to 1870-1899 brings up only five things including Hobbs and Blondel.

Then again classes boundaries can be confusing. This one's hierarchy is:

   326  . Refractor:
   333  .. With plural elements on both sides of main surface:
   334  ... Curved main surface:
  • I tried many of the classes 362/3xx under refractor and reflector. Very interesting is US 1092114, Prismatic glass reflector, issued 1914, classes 362/337, 362/361. It closely resembles what I seek, but has wavy prisms. The patent says "A transparent glass reflector having exterior radial reflecting prisms is well known in the art." The invention I recall is "well known!" But I keep searching all years thru 1920, and the well-known version is absent. I may look at my own files again, then visit the PO.
    – user7178
    Nov 10, 2013 at 10:25

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