You do not have permission to edit this page, for the following reasons:

This IP address has been blocked from editing Wikipedia.
This does not affect your ability to read Wikipedia pages.
Most people who see this message have done nothing wrong. Some kinds of blocks restrict editing from specific service providers or telecom companies in response to recent abuse or vandalism, and can sometimes affect other users who are unrelated to that abuse. Review the information below for assistance if you do not believe that you have done anything wrong.

The IP address or range 35.170.0.0/16 has been blocked (disabled) by ‪JJMC89‬ for the following reason(s):

The IP address that you are currently using has been blocked because it is believed to be a web host provider or colocation provider. To prevent abuse, web hosts and colocation providers may be blocked from editing Wikipedia.
You will not be able to edit Wikipedia using a web host or colocation provider because it hides your IP address, much like a proxy or VPN.
We recommend that you attempt to use another connection to edit. For example, if you use a proxy or VPN to connect to the internet, turn it off when editing Wikipedia. If you edit using a mobile connection, try using a Wi-Fi connection, and vice versa. If you are using a corporate internet connection, switch to a different Wi-Fi network. If you have a Wikipedia account, please log in.
If you do not have any other way to edit Wikipedia, you will need to request an IP block exemption.

How to appeal if you are confident that your connection does not use a colocation provider's IP address:
If you are confident that you are not using a web host, you may appeal this block by adding the following text on your talk page: ((unblock|reason=Caught by a colocation web host block but this host or IP is not a web host. My IP address is _______. Place any further information here. ~~~~)). You must fill in the blank with your IP address for this block to be investigated. Your IP address can be determined here. Alternatively, if you wish to keep your IP address private you can use the unblock ticket request system. There are several reasons you might be editing using the IP address of a web host or colocation provider (such as if you are using VPN software or a business network); please use this method of appeal only if you think your IP address is in fact not a web host or colocation provider.

Administrators: The IP block exemption user right should only be applied to allow users to edit using web host in exceptional circumstances, and requests should usually be directed to the functionaries team via email. If you intend to give the IPBE user right, a CheckUser needs to take a look at the account. This can be requested most easily at SPI Quick Checkuser Requests. Unblocking an IP or IP range with this template is highly discouraged without at least contacting the blocking administrator.

This block will expire on 05:20, 2 July 2025.

Even when blocked, you will usually still be able to edit your user talk page, as well as email administrators and other editors.

For information on how to proceed, please read the FAQ for blocked users and the guideline on block appeals. The guide to appealing blocks may also be helpful.

Other useful links: Blocking policy · Help:I have been blocked
Your IP address is in a range that has been blocked on all Wikimedia Foundation wikis. The block was made by ‪Jon Kolbert‬. The reason given is Open proxy/Webhost: See the help page if you are affected .
- Start of block: 05:38, 21 February 2024
- Expiry of block: 05:38, 21 February 2029
Your current IP address is 35.170.198.190. The blocked range is 35.170.0.0/16. Please include all above details in any queries you make. If you believe you were blocked by mistake, you can find additional information and instructions in the No open proxies global policy. Otherwise, to discuss the block please post a request for review on Meta-Wiki. You could also send an email to the stewards VRT queue at stewards@wikimedia.org including all above details.

You can view and copy the source of this page:

((Short description|Lantern using a Fresnel lens))
[[Image:Colortran Fresnel.JPG|thumb|A Fresnel with the lens open to show the ridges. There is no lamp in the instrument]]
A '''Fresnel lantern''' (pronounced ''frəˈnɛl or fruh-nel'') is a common [[Stage lighting instrument|lantern]] used in [[theatre]] that employs a [[Fresnel lens]] to wash light over an area of the [[stage (theatre)|stage]]. The lens produces a wider, soft-edged beam than a [[spotlight (theatre lighting)|spotlight]] or [[key light]], and is commonly used for [[back light]] and top light.

==Description==
[[Image:Fresnel lens.svg|thumb|upright|1: Cross section of a Fresnel lens
2: Cross section of a conventional [[Lens (optics)#Types of lenses|plano-convex lens]] of equivalent power]]

The distinctive [[Lens (optics)|lens]] used in a Fresnel lantern is named after its inventor, [[Augustin-Jean Fresnel]], who developed it for use in [[lighthouse]]s.  It has a 'stepped' appearance instead of the 'full' or 'smooth' face of other lenses. This allows the lens to focus the light by tilting each successive ring of glass slightly more steeply as its distance increases from the center. If the glass were completely flat, this would cause a corresponding pattern of circles of light, so Fresnel lenses are usually stippled on the flat side. This pattern of small bumps helps to break up the light passing through the lens and gives Fresnels their characteristic soft beam. This means that the intensity of the light is consistent across the spread of the beam of light, as opposed to being less intense around the edges as in an [[ellipsoidal reflector spotlight]] (ERS). 

The stepped lens design also causes less heat buildup than does a plano-convex lens of the same angle.<ref >((cite web
  | last =Brain  | first =Marshall
  | title =How does a Fresnel Lens work?
  | publisher =HowStuffWorks
  | url =http://science.howstuffworks.com/question244.htm
  | access-date =2006-12-12  
))</ref>

==Construction==
Theatrical Fresnel lanterns are typically made in three-, six-, or eight-inch lens diameters, with lamps ranging in power from 150&nbsp;W to 2,000&nbsp;W. The three-inch variety is referred to as an '''inkie'''. Fresnel lenses can be placed close to the light source and are inexpensive to produce.

In film lighting lenses range in size from 2 to 24&nbsp;inches, and lamp power between 150&nbsp;W and 24,000&nbsp;W.

Fresnels use a spherical [[mirror|reflector]], with the [[electrical filament|filament]] of the [[Lamp (electrical component)|lamp]] at its focus point. This effectively doubles the light delivered by the fixture, as all that is emitted backwards into the reflector is reflected back out the front. As with most lighting fixtures, the lamp and reflector cannot move independently, and are moved together as a unit to focus the beam. This is done by a slider on the bottom of the lantern, or a worm track and crank in the back of the unit. The lamps work best with their bases facing up, with bulb life shortened significantly when mounted upside down. 

Because the reflector of a Fresnel lantern cannot be larger than its lens aperture, the lamps are not very efficient: only the light emitted straight forward or backward (and redirected forward by the reflector) is utilized, with the rest absorbed by the casing as [[waste heat]].

The degree to which the lamp may be [[focus (optics)|focused]] is limited by the length of the housing. To reduce the width of the beam, the lamp and reflector are moved further back from the lens (spot focus). However, the farther back in the housing the lamp is placed, the more light is wasted in the housing.<ref >((cite book
  | last =Box
  | first =Harry C
  | title =Set Lighting Technician's Handbook: Film Lighting Equipment, Practice, and Electrical Distribution
  | publisher =Focal Press
  | date =1993
  | location =Boston
  | isbn =0-240-80161-X
  | url-access =registration
  | url =https://archive.org/details/setlightingtechn0000boxh
  ))</ref>

==Use==
[[Image: Zadok the priest.jpg|thumb|Fresnel lanterns in use at a classical concert; they can be seen silhouetted against the stage and each sports a [[barn door]]]]
In the theater and dance world, Fresnels are most often used for top or backlighting, at medium throw distances. In small venues, they are occasionally used for front light, although the relative lack of control, when compared to an [[Ellipsoidal reflector spotlight|ellipsoidal]], is a major disadvantage. The distinctive soft beam of a fresnel can make it very useful as a [[special (lighting)|special]] in certain situations.
 
While the focus can alter the size of the beam, the distinctive scatter of light that the Fresnel lens emits also requires a way of controlling its shape. Since Fresnels cannot use internal shutters, such as those found in an ellipsoidal spotlight, they are often fitted with distinctive [[barn doors]] to control the spill and shape the beam of light. These are large metal flaps that may be mounted just beyond the color slot at the front of the lantern. They are colloquially known as "Harris Flaps" in the [[United Kingdom]] theatre industry.<ref>((Cite web |last=Chand |first=Tushar |date=1 May 2021 |title=Lighting for Cinema, Lighting Controls |url=http://www.dspmuranchi.ac.in/pdf/Blog/UNIT%20-%204%20-%204.3%20-%20LIGHTING%20CONTROLS%20PART%20-%201%20BARN%20DOOR.pdf |access-date=1 June 2022 |website=Dr. Shyama Prasad Mukherjee University))</ref> <ref name="oneohfour">Shelly, p.104</ref>

== References ==
((Refimprove|date=January 2010))
((reflist))


((Stagecraft))

((DEFAULTSORT:Fresnel Lantern))
[[Category:Stage lighting instruments]]

Pages transcluded onto the current version of this page (help):

Fresnel lantern (edit)
Template:Ambox (view source) (template editor protected)
Template:Cite book (view source) (protected)
Template:Cite web (view source) (protected)
Template:Find sources mainspace (view source) (template editor protected)
Template:Hlist/styles.css (view source) (protected)
Template:Icon (view source) (template editor protected)
Template:Main other (view source) (protected)
Template:More citations needed (view source) (template editor protected)
Template:Navbox (view source) (template editor protected)
Template:Pagetype (view source) (protected)
Template:Refimprove (view source) (template editor protected)
Template:Reflist (view source) (protected)
Template:Reflist/styles.css (view source) (protected)
Template:SDcat (view source) (protected)
Template:Short description (view source) (protected)
Template:Short description/lowercasecheck (view source) (protected)
Template:Stagecraft (edit)
Module:Arguments (view source) (protected)
Module:Category handler (view source) (protected)
Module:Category handler/blacklist (view source) (protected)
Module:Category handler/config (view source) (protected)
Module:Category handler/data (view source) (protected)
Module:Category handler/shared (view source) (protected)
Module:Check for unknown parameters (view source) (protected)
Module:Citation/CS1 (view source) (protected)
Module:Citation/CS1/COinS (view source) (protected)
Module:Citation/CS1/Configuration (view source) (protected)
Module:Citation/CS1/Date validation (view source) (protected)
Module:Citation/CS1/Identifiers (view source) (protected)
Module:Citation/CS1/Utilities (view source) (protected)
Module:Citation/CS1/Whitelist (view source) (protected)
Module:Citation/CS1/styles.css (view source) (protected)
Module:Disambiguation/templates (view source) (protected)
Module:Find sources (view source) (template editor protected)
Module:Find sources/config (view source) (template editor protected)
Module:Find sources/links (view source) (template editor protected)
Module:Find sources/templates/Find sources mainspace (view source) (template editor protected)
Module:Icon (view source) (template editor protected)
Module:Icon/data (view source) (template editor protected)
Module:Message box (view source) (protected)
Module:Message box/ambox.css (view source) (protected)
Module:Message box/configuration (view source) (protected)
Module:Namespace detect/config (view source) (protected)
Module:Namespace detect/data (view source) (protected)
Module:Navbar (view source) (protected)
Module:Navbar/configuration (view source) (protected)
Module:Navbar/styles.css (view source) (protected)
Module:Navbox (view source) (template editor protected)
Module:Navbox/configuration (view source) (template editor protected)
Module:Navbox/styles.css (view source) (template editor protected)
Module:Pagetype (view source) (protected)
Module:Pagetype/config (view source) (protected)
Module:Pagetype/disambiguation (view source) (protected)
Module:Pagetype/setindex (view source) (protected)
Module:Pagetype/softredirect (view source) (protected)
Module:SDcat (view source) (protected)
Module:String (view source) (protected)
Module:Unsubst (view source) (protected)
Module:Wikitext Parsing (view source) (protected)
Module:Yesno (view source) (protected)

Return to Fresnel lantern.

Retrieved from "https://en.wikipedia.org/wiki/Fresnel_lantern"