LED output vs. Incad. - Page 1
Forum section: electronics / projects

author: JohnS_AZ
author_rank: Frequent Contributor
timestamp: October 28, 2010, 04:56:44 pm
content: Does this pass the sanity test?I have several outdoor light fixtures that all use 12 watt incandescent bulbs. The bulbs cost about between $2 and $3, and all have to be replaced a couple times a year. Obviously using LEDs would be smarter both in terms of cost and energy waste.I looked up the bulb on the Philips website and found that it puts out about 120 lumens.I found a website that states that Mcd = Lumens * 79.5544Thus, 9546 Mcd of LED should equal the output of the original incad. lamp ... right?I have a bunch of 1500 Mcd LED here so this weekend I'm going to wire up a bunch and see what it looks like, but thought I'd run it past you guys for insight before soldering it all together.

author: Simon
author_rank: Unknown
timestamp: October 28, 2010, 05:02:41 pm
content: well leds are more efficient so if your using near the same wattage or no less than 1/3 I think your safe to say that your not making a loss on light

author: qno
author_rank: Frequent Contributor
timestamp: October 28, 2010, 07:08:06 pm
content: There is a small difference in light output.The incandescent lamp will send light of the whole visible spectrum (and lot of IR).The LED's, assuming their white, will have a combination of RGB or a blue led with a fluorescent layer making it look white-ish.Leds are also much more focused. So the total light spread/flood will not be as the light bulb.Cooling of the LED is very important for longevity of the LED. Also remember that the sensitivity of the eye is logarithmic.Best thing, i think, is do some experiments. Make some notes and maybe a picture and place it on the web.I am interested

author: Mechatrommer
author_rank: Super Contributor
timestamp: October 28, 2010, 07:32:48 pm
content: Quote from: JohnS_AZ on October 28, 2010, 04:56:44 pm9546/1500 = 6.362 LEDs right?Quote from: qno on October 28, 2010, 07:08:06 pmuse ventilated diffuser. agree on experiment, me interested too.

author: JohnS_AZ
author_rank: Frequent Contributor
timestamp: October 28, 2010, 08:07:04 pm
content: I shouldn't have to worry about heat for this. The 1500 Mcd LEDs I have are plain T 1 1/2, water clear body, amber output.

author: sonicj
author_rank: Frequent Contributor
timestamp: October 28, 2010, 08:26:49 pm
content: neighbor a few houses down installed led landscaping lights... if he adds anymore fixtures, aircraft will be mistaking his driveway as a runway!i bought some nice led stuff from lowes when it went on clearance. the kit i bought looks great powered from ac-dc converter. same kit looks like garbage when powered from the solar charged li-ion battery. i think the floods have 3 white 5mm leds, the pathway markers have a single white led. the floods look neat illuminating plants. those look better in pairs. not bright enough to illuminate address numbers mounted on the house or a flag though...-sj

author: ziq8tsi
author_rank: Regular Contributor
timestamp: October 28, 2010, 10:16:34 pm
content: Quote from: JohnS_AZ on October 28, 2010, 04:56:44 pmThe candela is one lumen per steradian. To convert between them in general you need to know the exact radiation pattern of the device, so that you can integrate or differentiate over a spherical angle.If the device emits uniformly in all directions, then cd = lm / 4 pi. Which does give mcd = lm * 79.55. But this is a very unlikely emission pattern for an LED.QuoteIn the direction of peak emission, yes. If the original bulb had no kind of reflector.If you cannot find the total lumen output for the LEDs, then Simon's electrical power calculation will probably give a more reliable first estimate. The incandescent was 10 lm / W. The LEDs may be 30. (The best LEDs for lighting reach 100 lm / W, but if the datasheet does not even quote lumens then I would not expect that.)

author: JohnS_AZ
author_rank: Frequent Contributor
timestamp: October 28, 2010, 10:44:15 pm
content: Thanks ziq8tsi.So then, as I understand it, I will not have to reproduce the total lumen output of the original incandescent lamps since ...4 of the fixtures are coach lights. The light shines out of these fixtures horizontal to the ground and 365 degrees around. Light from the current bulb that shines upward and downward is wasted. The LEDs can all be aimed circumferentialy (sp??). The remaining fixtures are downward shining "pot" lights. obviously the LEDs would all point down.

author: TechGuy
author_rank: Regular Contributor
timestamp: October 28, 2010, 10:54:59 pm
content: The average incandescent lightbulb at 120 VAC puts out about 17 lumens per watt. A 100 watt incandescent bulb will put out about 1700 lumens. Your 12 Watt bulbs probably put out about 204 lumensAlso consider the LED emission angle. Most LEDs have a small emission angle of about 15 to 180 degrees. A incandescent will have an emission around 300 degrees. Another words the output of a incandescent will be spread out more, where an LED will be focused on a small area. The limited emission angle of LEDs is caused by the shape of the LED, which is a small flat square plate and light is only emitted from one side. Perhaps in the future LEDs with a curved surface will be producted to prived a wider angle.FWIW: I would recommend waiting until LEDs can match the output of a 100 watt light bulb. The bulk of LEDs max out around 800 lumens. Considering the development of white high output LED is pretty new, I think we will see better products in the next two years.You also have to be careful. White LEDs are really UV-LEDs with a phosphor coating to convert UV light into white light. Some of the cheap White LED imports don't use a sufficient and uniform phosphor coating which permits excessive UV-B emissions. Long term exposure to UV-B light can cause cateracts and other eye-related problems. The cheaper bulbs emit a blue tint.You can also buy LED light bulbs, which would be a better option than manually soldering a bunch of white LEDs. A quick google search will turn up dozens of suppliers. You can also buy high output white LEDs from LEDs also need a constant current driver to deliver the best output without causing them to fail or have a reduced operating life.Bridgelux makes some of the brightest LEDs on the market:http://bridgelux.com/assets/products_portfolio/BridgeluxLEDArray_DataSheet.pdf

author: Zero999
author_rank: Super Contributor
timestamp: October 29, 2010, 04:48:21 pm
content: Quote from: TechGuy on October 28, 2010, 10:54:59 pmThat's not always the case. Most modern white LEDs use 430nm deep blue dies with a broad spectrum yellow phosphor and the UV based LEDs use near UVA (typically 380nm to 400nm) which is much safer than dangerous cancer causing UVB.The colour temperature determines whether it's bluish or more yellowish, you can buy cheap yellowish LEDs or expensive bluish LEDs. The main difference is with the cheap LEDs, the colour temperature will not be very well controlled and will change more throughout the LED's lifetime.

author: TechGuy
author_rank: Regular Contributor
timestamp: November 02, 2010, 01:30:58 am
content: Quote from: Hero999 on October 29, 2010, 04:48:21 pmSlight correction. Its the blue light emitted by LEDs that is harmful. See this article:http://www.mdsupport.org/library/hazard.htmlQuoteQuote

author: EEVblog
author_rank: Unknown
timestamp: November 02, 2010, 02:15:17 am
content: Forget using any LEDs's that only specify their output in MCD.Proper lighting class LED's always spec in Lumens.One single Cree XPG LED can easily do 120 Lumens.But it's all about the colour rendition, angle etc as to whether or not your eyes perceive the LED being "as bright as" the old incandescent.Dave.

author: slburris
author_rank: Frequent Contributor
timestamp: November 02, 2010, 03:21:00 am
content: I've just been using the Portfolio LED lights from Lowes, 3.5watts:http://www.lowes.com/pd_284339-2121-WT-S41_0__?productId=1080547&Ntt=portfolio+led&pl=1&currentURL=%2Fpl__0__s%3FNtt%3Dportfolio%2Bledand the new Malibu 7watt light from Home Depot. The 7w Malibu lightis supposed to be about the same as a 20w halogen:http://www.homedepot.com/h_d1/N-5yc1vZ1xhc/R-202059598/h_d2/ProductDisplay?langId=-1&storeId=10051&catalogId=10053I'm slowly putting this stuff in everywhere, nominally to save energy,but I'm just really really tired of replacing burned out bulbs :-)By the time you build a constant current power supply to drive any highpowered leds you have, do the thermal calculations, then somehow machinea heatsink to meet the needs, you're already spending a significantpart of the cost to just go buy new fixtures....Scott

author: JohnS_AZ
author_rank: Frequent Contributor
timestamp: November 02, 2010, 04:05:01 am
content: I generally agree with you both, but I have a unique situation.I want to replace the lamps in existing vintage metal fixtures. They currently use, and I'm quite happy withthese. They're only 7 1/2 watts so there are no CFL options (which suits me fine because I loathe and detest idiotic CFLs). Most all of the LED lamps I've seen (as well as all high power LEDs) are directional, and these need to cast light through 360 degrees.Now, I also have to please Lisa, queen of the manor.She and I both despise the light cast by white LED landscape lighting. She also would be very disappointed to loose the old fixtures. And the final factor in this situation is the fact that I already have about 900 1,500 mcd LEDs. I kind of stole them in an eBay auction... the listing said "1200 1500 Amber LDE Bulbs, Bright". I saw what they were in the photo and got them for the $0.99 minimum bid. (I've since given away a few handfulls).Since these are bright, but not "high power", I really don't have to worry about power supplies or heat sinks. Since I only have to make up the light from a fairly low wattage bulb it's not as if I'll be needing a hundreds of them. And what's more I don't have to buy anything at all to give it a shot.As an aside, I breadboarded a string of 7 LEDS, and then 14. I'm guessing 21 LEDs will just about equal the original bulb.

author: FreeThinker
author_rank: Frequent Contributor
timestamp: November 02, 2010, 03:55:03 pm
content: Well if your experiments fail then you could try thesehttp://www.ledon-lamp.com/en/product_overview.htmThey are up to 60w and in arange of form factors.My wife was given a couple of these by her company 6w Led 40w(eqiv) ,340lm at 2900k.A nice warm white not dissimilar to an incandescent lamp and SO much better than those crappy cfl.edit.Just had a look on the website and these are about 25 euros each.Still with a claimed life of 25 years thats only 1 euro/annum.

author: Zero999
author_rank: Super Contributor
timestamp: November 02, 2010, 07:26:43 pm
content: Quote from: TechGuy on November 02, 2010, 01:30:58 amI've read that before and am cynical that LED lighting would cause any more damage than daylight which also contains a significant blue wavelengths.

author: sonicj
author_rank: Frequent Contributor
timestamp: November 02, 2010, 11:08:23 pm
content: these are fun/easy to play withpiranhai think they are becoming popular in automotive. i was looking at some tail lights at pepboys the other day and they had piranhas under the lens.dx has all sorts of interesting leds, drivers, fixtures, bulb replacementsdealextremei just orderedthis guyfrom digikey. 388lm in a 4000k neutral white. not sure what im going to put it in yet...-sj