The Electronic Theatre Controls (ETC) Source Four (also known unofficially as Source 4 or S4) is an ellipsoidal reflector spotlight (ERS) used in stage lighting. First released in 1992, the Source Four was invented by David Cunningham and features an improved lamp and reflector compared to previous ERS designs, tool-free lamp adjustment, and a rotating, interchangeable shutter barrel. The Source Four is widely used by professional theaters across the globe.
The Source Four is the first ERS to use a faceted borosilicate reflector behind the lamp . Nearly all stage lights have some form of reflector positioned behind the lamp to reflect otherwise wasted light out of the front of the instrument. The Source Four's reflector is dichroic, meaning that it reflects light of only certain wavelengths. The Source Four's reflector reflects back 95% of the visible light striking it, while allowing over 90% of the infrared radiation (heat) to pass out the back of the instrument. This produces a much cooler light which is less destructive to gobos or color gels at the front of the fixture, and reduces localized heating of the lighting target.
I should have stayed in bed today
I couldn't think of a positive thing to say
My friends all hate me now
I was selfish and realize now
I have it a little time
I thought about it a while
ask to forgive and forget
Crack a joke and a smile
It's hard to say you're sorry
when you know that you were wrong
The weight of hurting words
We often carry on
The annoying things I don't mind so much anymore
I've learned to tolerate the annoying four
I won't let the sun go down
when I've made a mistake
I'd make right what I've wronged