The Boogie Man Posted January 6, 2007 Share Posted January 6, 2007 Ok, here goes. As most around here know I'm just on the point of putting my hand in my pocket to purchase some lights. I'm ok for a while with the idea of led par cans ( due to the ohm-age draw ), but then in a post about them or lighting someone with them will state they're just not bright enough.So: A pitch black room 10mtrs sq. A single 100watt household bulb (sorry lamp). Illuminate the room. This we all know and can use as a control.Turn off light, replace with a 300watt par can ( with white or very light coloured lamp). Three times brighter than control?Turn off light, replace with a 151 led par can (with white or very light coloured lamp ). brightness compared to above lamps? I know no-one has done this as an experiment, but if anyone with all of the above has an educated guess, please post it.On a related note, sound has a spl level used to compare ratings etc. Does light not have have a similar guide. Per square metre coverage? Yes I know we are constantly talking about leds and comparing them to standard par cans, but in the absence of a manufacturers spec list a user based guide may help a lot of people.Baz Link to comment Share on other sites More sharing options...
StevieR Posted January 6, 2007 Share Posted January 6, 2007 There are three main units of measurement for light. Lumens - this refers to the total light output of a source - e.g. a lamp. Footcandles and LUX - used to describe the amount of light falling on a given area. LUX is the metric version of this. 1 LUX = 1 Lumen per square metre. Link to comment Share on other sites More sharing options...
niclights Posted January 6, 2007 Share Posted January 6, 2007 Everyone wants these figures, but I don't think a way has been found to accurately compare in this manner. There is good reason why manufacturers don't quote & even if you call them and ask (ie. example of outdoor floodlight replacement), they will refuse to say because they just don't know! I assume this is due to the difference in source, wavelength and the way our eyes perceive this. Link to comment Share on other sites More sharing options...
paulears Posted January 6, 2007 Share Posted January 6, 2007 And of course the beam angle makes a big difference. Take a Fresnel on full spot - much brighter than on full flood? So the LEDs are dimmer, but wider. The PARS brighter and narrower. Even with a lightmeter - easily available, the figures don't make themselves easy to compare. A 100W source, used as the 'control' doesn't help much because nobody knows how bright their version is? Is a Philips brighter than an Osram, are the Tesco own brands different or the same. The question really involves subjectivity. A single LED fixture looks bright in a dark room. It does make choosing a different type of light source a bit of a gamble- but I can't think of a solution. Link to comment Share on other sites More sharing options...
Don Allen Posted January 6, 2007 Share Posted January 6, 2007 Fundamental flaw in your experiment is not taking beam widths into account. Your control source has an approximate 360 degree beam width looking on a single plane but it is radiating as a sphere so the light output which comes from heating the filament to a radiant frequency is spread out all over the room. The Par can is radiating in a very narrow beam in comparison to the control source at a particular radiant frequency. The led fixture is made of individual LEDs of some discrete beam width radiating at some radiant frequency. Your light meter has a sensor, what is it's spectral response as you could get misleading readings. Cheap light meters are not accurate, mainly useful for A/B comparisons in this case. Without the manufacturers data which they do not usually give out if from Asia as they are on a profit basis, not service basis, you do not know what wavelength the LEDs are radiating on. Also there are production tolerance spreads. You should be able to get the data on the reference lamp and the Par lamp. At present it is mainly a subjective comparison due to all of the errors involved. Read up on the units of light to understand how to use it accurately. If you want to compare two light sources using Lux, both readings need to be taken in the centre of the beam. (Ever been to a trade demo where they are comparing two "similar" fixtures, but the opposition's unit has been "detuned") Link to comment Share on other sites More sharing options...
The Boogie Man Posted January 6, 2007 Author Share Posted January 6, 2007 Cheers guys, whilst I was fully expecting the novel experiment to be shot down as unscientific, I was hoping some one with a couple of units would be able to say "yes an led is x% less bright or brighter than x par can.baz Link to comment Share on other sites More sharing options...
johnhuson Posted January 6, 2007 Share Posted January 6, 2007 I'm pressuming you've read it before, but the most useful comparisons I have seen are in This Post by niclights in the LED PAR's thread. Shows a direct comparison with a 650w PC with similar beam angle, results speak for themselves I think! Link to comment Share on other sites More sharing options...
The Boogie Man Posted January 7, 2007 Author Share Posted January 7, 2007 cheers John, Yes I had read the original post, But as it was nearly a year ago I'd wondered if any changes/ improvements had taken place. Just wanted to make sure I had the latest Info before parting with any crispy paper from mummy's purse. Link to comment Share on other sites More sharing options...
musht Posted January 8, 2007 Share Posted January 8, 2007 http://en.wikipedia.org/wiki/Lux Data for any decent manufacturers fixture should be available, some reps might be a bit shy because raw lumens comparison between MH/HPS floodlighting and LED is absolutely huge, but beware of lies, damned lies and statistics. http://en.wikipedia.org/wiki/Candela AKA Candlepower, is a directional measurement, same amount of power with narrower beam can have higher cd figures. Popular way to quote big numbers, 15,000,000 candlepower torch anyone?, meaningless without the beam angle. Nic`s photos are very handy as is the photo on same thread of candlelit service.But it dosen`t seem that any of the posters in 35 pages or something have a 300w Par 56 and camera to hand at same time which would help make a more typical comparison. Where the 56 obliterates the LED. Brightness is all relative though and in room mainly lit by 60W amber glow lamps, a n boozer somewhere, a few cheap LED pars will certainly make you stand out. Link to comment Share on other sites More sharing options...
lonfire Posted January 8, 2007 Share Posted January 8, 2007 hi guys,I'm talking to various suppliers of LED products with a view of importing them.. the data they have given me is this:177x10mm LED parcan - 5,200 lumens/1 meter24x1w high power leds - 10,000 lumens/1 meter these are nice lights with LED display on the back instead of dip switches.. I don't know how accurate these figures are or how they compare to other lights.. if anybody else has any figures like these for other lights I'd be interested.. as others have said the beam angle and quality of the meter will play a big part in the readings.. rgdschris http://www.useful4all.com/ledparcans.JPG Link to comment Share on other sites More sharing options...
musht Posted January 8, 2007 Share Posted January 8, 2007 hi guys,I'm talking to various suppliers of LED products with a view of importing them.. the data they have given me is this:177x10mm LED parcan - 5,200 lumens/1 meter24x1w high power leds - 10,000 lumens/1 meter Wrong measurement ;-), we`ll take it as a translation error. Lumens total light output, distance has nothing to do with it, its a measure of Total Luminous Flux, all the light , not just light in a certain direction. Measurement should be Illuminance in Lux, which is lumens per square meter. CK talks a good data sheet, their numbers at least are reasonably reliable..... Comparable fixture that uses 36 1W LEDs, high quality big brand Cree dice, currently brightest available. CK Colorblast 12, bearing in mind 50% more LEDs, http://www.colorkinetics.com/support/datas...olorBlast12.pdf Total light output, all colours on : 642 Lumens Illuminance, pointing straight down at the meter at 1m: 15 231.1 Lux This can be fiddled with like cd ,by altering beam angle, CK quote 10 degrees. So 10K *LUX* out of a 24W unit does not look out of order, but still more likely to have been measured using back of a fag packet ;-) Big LEDs are easier to thermally manage and really are more the future than cramming loads of small LEDs on to a board. Link to comment Share on other sites More sharing options...
lonfire Posted January 8, 2007 Share Posted January 8, 2007 So 10K *LUX* out of a 24W unit does not look out of order, but still more likely to have been measured using back of a fag packet ;-) indeed.. when I get the samples I'll put them side by side with a 300w par56/500w par64 and a showtec LED par64 and get some photos.. hopefuly we'll be doing them at a reasonable price compared to other 24x1w LED parcans around.. rgdschris Link to comment Share on other sites More sharing options...
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