Founded in 1896, Universal Electric Stage Lighting Company a/k/a Kliegl Brothers originated the term "Klieglight" to describe their carbon arc spotlight, as shown in their 1913 catalog (below, left) and in trade ads dating back to 1905.
Kleiglight held the distinction of getting its name into the dictionary as early as 1932.

--and likewise "Klieg Eyes" was coined to describe a popular and exotic moving picture disease as early as 1916. 
Not even handsome and manly stars like Wallace Reid, fortified by healthful morphine, were immune to the perils of "Klieg Eyes."
Here are just a few of the Klieglights at Paramount that troubled Wally Reid. 
A slight setback for Kliegl occurred when their arc lights were deemed too noisy for use in shooting talkies. 
However a sweetheart contract as exclusive stage lighting supplier to Radio City Music Hall allowed the brothers Kliegl to (a) weather the depression and (b) invent a new Klieglight, popularly known as a leko, the Century trade name.  Kliegl also invented the fresnel.
The relative contributions of the two brothers are not known, but John excelled in mortality, outliving Anton who died in 1928 while visiting his native Bavaria.  "The carpenters were Irish and the electricians were German," observed a hand from Local One.  Click on the blue space beneath John's 1959 obit to enlarge it.
During the 1950's and 60's Kliegl equipped nearly every TV studio in the country and in the 1970's re-equipped them for color.

The omnipresent Performer was the last hurrah for Kliegl (who invented the SCR dimmer) and they celebrated their 100th birthday in 1996 by folding, according to the wiki.  Click on the blue space beneath the Performer to enlarge it.
Here then is the 1913 catalog, one of many contained in the Joel E. Rubin Collection at Ohio State in Columbus.   Right-click on the blue space immediately beneath any catalog page to enlarge it; right-click again for super-large.  To download the entire catalog, click here.

Pages 76 through 78 contain a complete and detailed electrics plot for the 1903 Metropolitan Opera House installation and a conversion chart from "c.p." (candle power) to watts is included.  Thus according to the chart, the "4000 C.P." Open Box Arc Light on page six emits the equivalent of 14,000 watts. 
Thanks to Paulene Spika. 
June, 2023