Street light interference phenomenon

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Not to be confused with Streetlight effect.
A concrete streetlight on its mounting pole using a high intensity lamp fixture

Street light interference, or SLI, is an alleged anomalous phenomenon where a person seems to turn off (or sometimes on) street lights, or outside building security lights, when passing near them.

Although street lights can turn off by chance, such as high pressure sodium street lights cycling (turning on and off repeatedly) at the end of their life cycle, believers in street light interference tend to claim that it happens to them personally on a regular basis, more frequently than chance would explain. Some propose paranormal explanations for SLI, sometimes based on scientific terminology, such as the explanation that electrical impulses in their brain interfere with the workings of electric lights. Anecdotes about people's experiences of SLI have been reported by news sources.[1]

SLI has never been demonstrated to occur in a scientific experiment, and those who claim to cause it have been found to be unable to reproduce the effect on demand; they give the explanation that the effect is not within their mental and physical control.[2] Many times they do report, however, that it occurs with specific lamps and not just randomly shutting off street lights or electrical lamps in general.[3][4]

Hilary Evans and the The SLI Effect[edit]

Hilary Evans, an English author who writes about paranormal subjects, coined the word "SLIder" to refer to someone who causes this effect, in his book The SLI Effect.[5] In this book on page 15 he explains that a wide variety of street lamp types show

In the preface of the book Evans says,

On page 16 he explains what seems most likely to be happening,

Skepticism of SLI[edit]

The skeptical explanation to claims of SLI is to consider it an example of correlation not implying causation, or of confirmation bias: people are much more likely to notice when a nearby street light turns on or off than they are to notice a light turning on or off at a distance, or a street light in a steady state at any distance. This is compounded by a failure mode of street lights, known as "cycling", in which street lights of the high pressure sodium type turn off and on more frequently at the end of their life cycle.[7] A high pressure sodium engineer at General Electric, quoted by Cecil Adams, summarizes SLI as "a combination of coincidence and wishful thinking".[7] Massimo Polidoro notes in Skeptical Inquirer that "Paranormal phenomenon is the least likely possibility."[8]


  1. ^ ASSAP Early SLI (street lamp interference) News reports from the later 1980s to the early 1990s.
  2. ^ SLIders & the Streetlight Phenomenon, in's "Paranormal Phenomena", by Stephen Wagner.
  3. ^ The SLI Effect (PDF) by Hilary Evans (Pub: Frome, ASSAP - London, England 1993, 2005) pp 12, 23, 24, 25, 26.
  4. ^ Cool - Street Light Interference
  5. ^ The SLI Effect by Hilary Evans (Pub: Frome, ASSAP - London, England 1993, 2005 ISBN 0-9521311-0-2
  6. ^ Evans, p. 16
  7. ^ a b Cecil" Adams. "Can some people extinguish streetlamps by means of their bodily emanations?" In "The Straight Dope", October 28, 1994. Retrieved April 6, 2007.
  8. ^ Polidoro, Massimo (November 2008). "The Curious Case of Street Lamp Interference". The Skeptical Inquirer (Amherst, NY: Committee for Skeptical Inquiry) 32 (6): 21–22. Retrieved 2008-12-10. [dead link]

See also[edit]


  • Waymouth, John (1971). Electric Discharge Lamps. Cambridge MA: The MIT Public Press. ISBN 0-262-23048-8. 
  • Spencer, John The Paranormal: a Modern Perspective, 160 p. Hamlyn, London (1992) [Paranormal Phenomena].
  • Street Light Interference article published in scientific magazine Omni, September 1990 journalist Dennis Stacy,
  • Street Light Interference articles reported by Robert McMorris Omaha World-Herald several issues January 1990.
  • The Paranormal Investigator's Handbook by Valerie Hope. Publisher by Sterling Co. 1999. ISBN 1-85585-703-0.
  • Evans, Hilary, The SLI Effect, [Frome] : ASSAP, 1993, ISBN 0-9521311-0-2

External links[edit]