{"id":206,"date":"2014-08-12T22:04:53","date_gmt":"2014-08-13T02:04:53","guid":{"rendered":"https:\/\/designinglight.com\/?p=206"},"modified":"2014-08-12T22:04:53","modified_gmt":"2014-08-13T02:04:53","slug":"dimming-that-doesnt-dim-off","status":"publish","type":"post","link":"https:\/\/designinglight.com\/?p=206","title":{"rendered":"Dimming That Doesn’t Dim Off"},"content":{"rendered":"

Recently a designer specified 0-10V dimming for a series of LED downlights.\u00a0 The electrician powered the LEDs by connecting them to a nearby breaker panel.\u00a0 The 0-10V control signal was generated by the lighting control system.\u00a0 This was a simple system that should have worked with no problems.\u00a0 Much to everyone\u2019s surprise the lights would dim but they wouldn\u2019t go off!\u00a0 What happened?<\/p>\n

Dimming light sources other than incandescent is a technical challenge.\u00a0 It requires the ballast (for fluorescent, HID, cold cathode, etc.) or the driver (for LEDs) to precisely control the amperage and the voltage, and may also require converting the incoming AC to a DC output (for some LEDs).\u00a0 This is difficult for fluorescent and HID lamps because the electricity must arc from one side of the lamp to the other, and at low power levels that arc simply fails.\u00a0 Dimming LEDs often results in a visibly jittery dimming curve as well as a jump to zero when dimming down and a jump to on when dimming up. (This article<\/a> in Electrical Construction & Maintenance is a good overview of the problems with dimming LEDs.)<\/p>\n

In architectural lighting, however, the inability to dim all the way to zero is usually not seen as a problem.\u00a0 Typical dimming applications such as classrooms and meeting rooms may want to dim lights for a presentation, but some light is still desirable so that attendees can see each other for discussion and see their desktop to take notes. Dimming is acceptable as long as the dimming is smooth down to a minimum light level.\u00a0 In these installations the drop from, say, ten percent to zero isn\u2019t an issue because it doesn\u2019t happen until the room is empty and the lights are turned completely off.<\/p>\n

With 0-10V dimming, though, the dimmer or driver is powered by the incoming line voltage, so its always operating.\u00a0 As a result, its minimum operating capacity is also the fully dimmed state.\u00a0 A 100-10% ballast or driver, for example, has a minimum output of 10% not zero.\u00a0 When the fader is at the bottom of its travel we would normally expect the lights to go off, but they only go to 10%.\u00a0 Here\u2019s a graph showing the performance of representative LED fixtures dimmed with a 0-10V dimmer.<\/p>\n

\"Source:<\/a>
Source: U.S. DOE<\/figcaption><\/figure>\n

The solution is to provide separate switching of the line voltage delivered to the fixture.\u00a0 Most wallbox dimmers have a toggle switch below the fader so that the fixture can be shut off at any time.\u00a0\u00a0\u00a0 Here\u2019s a schematic of a simple circuit.<\/p>\n

\"Source:<\/a>
Source: U.S. DOE<\/figcaption><\/figure>\n

Other solutions come from other dimming techniques, including three-wire and four-wire dimming where the line voltage and the control signal come out of the same device.\u00a0 This guarantees that at a minimum state power to the fixture is shut off.\u00a0 Other control protocols, notably DMX512, and the electronics that utilize them can usually dim to zero.<\/p>\n","protected":false},"excerpt":{"rendered":"

Recently a designer specified 0-10V dimming for a series of LED downlights.\u00a0 The electrician powered the LEDs by connecting them to a nearby breaker panel.\u00a0 The 0-10V control signal was generated by the lighting control system.\u00a0 This was a simple system that should have worked with no problems.\u00a0 Much to everyone\u2019s surprise the lights would … Continue reading Dimming That Doesn’t Dim Off<\/span><\/a><\/p>\n","protected":false},"author":1,"featured_media":0,"comment_status":"open","ping_status":"open","sticky":false,"template":"","format":"standard","meta":{"_jetpack_newsletter_access":"","_jetpack_dont_email_post_to_subs":false,"_jetpack_newsletter_tier_id":0,"_jetpack_memberships_contains_paywalled_content":false,"_jetpack_feature_clip_id":0,"_jetpack_memberships_contains_paid_content":false,"footnotes":"","jetpack_publicize_message":"","jetpack_publicize_feature_enabled":true,"jetpack_social_post_already_shared":true,"jetpack_social_options":{"image_generator_settings":{"template":"highway","default_image_id":0,"font":"","enabled":false},"version":2},"jetpack_post_was_ever_published":false},"categories":[9],"tags":[67,56,25,23],"class_list":["post-206","post","type-post","status-publish","format-standard","hentry","category-controls","tag-controls","tag-dimming","tag-led-control","tag-led-dimming"],"jetpack_publicize_connections":[],"jetpack_featured_media_url":"","jetpack_shortlink":"https:\/\/wp.me\/p4gZSw-3k","jetpack_sharing_enabled":true,"jetpack_likes_enabled":true,"jetpack-related-posts":[{"id":61,"url":"https:\/\/designinglight.com\/?p=61","url_meta":{"origin":206,"position":0},"title":"A Challenge for LED Luminaires","author":"Jason Livingston","date":"January 20, 2014","format":false,"excerpt":"Today I was at an LED \"shootout\" at the New York City office of Barbizon (special thanks to John Gebbe and Scott Hali). \u00a0We were looking at products that might be used in a specific application - that of lighting an auditorium or theatre. \u00a0The shootout was between 26 fixtures\u2026","rel":"","context":"In "Color"","block_context":{"text":"Color","link":"https:\/\/designinglight.com\/?cat=12"},"img":{"alt_text":"","src":"","width":0,"height":0},"classes":[]},{"id":622,"url":"https:\/\/designinglight.com\/?p=622","url_meta":{"origin":206,"position":1},"title":"MIT Creates Incandescent Lamp As Efficient as LEDs","author":"Jason Livingston","date":"April 25, 2016","format":false,"excerpt":"Researchers at MIT and Purdue University have demonstrated an incandescent lamp with an efficacy of 6.6 percent, and with a potential efficacy as high as 40 percent. 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