Yaksplt - My Error in LED brightness (mcd) in earlier post

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TheMadNucleus

Aquarium Advice Freak
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In an earlier post several of us were discusing the possibility of using arrays of LED's to light a complete aquarium. We were looking for ways to overcome a few problems that LED's present 1.) Limited bandwidth, 2.) narrow radiation beam and 3.) Luminous Flux (brightness)

In this thread I erroneously posted that LED brightness is rated in micro-candela when in fact they are rated in milli-candela. For those that care, I wanted to correct this. Yaksplat you were correct in your assumption, it is milli-candela. I've been playing arround with 6000 mcd Blue LED's and yikes - they are pretty bright, an array of 100 (10x10) will provide considerable output, however - still very tightly focused.

I know this will be of particular intrest to Yaksplat and a few others.

Sorry about that.
 
I was supposed to get back to you guys with some related information I believe but I had just finished building my computer a few weeks ago and forgot about it...

December 2003 vol 9 num 11 issue of Compound Semiconductor (III-V).

As a note lumens/m^2 is equivalent to candela/m^2 and both measure luminosity.

Watts/m^2 is a measure of radiance (I remember someone had a question about this before but I didn't have a chance to answer).

You can now buy 183,000 mcd LEDs (183 lumen or candela) at digi-key but at a price of $24.63 per unit unless you buy a large number. 60 degree viewing angle though it is green: http://dkc3.digikey.com/pdf/T041/1271-1272.pdf
 
Thanks Patryuji,

Those LEDs at digikey look pretty interesting (the 183,000 mcd units are really arrays as far as I can tell - hence the power and wider view angle). Still, the 60 deg is mighty narrow compared with the output of a MH lamp. Also, it was not specific as to the output at the 60 degrees, i.e. there was no graph showing the units actuall dispersion (i.e. everything beyond 30 degrees might be very minimal).

Also, I'm not sure but seems you have an error in your conversions. I believe A lumen and candela can not be directly converted as they measure two different types of luminosity. However 1 Lumen / m² = 0.092903 Footcandle.

As I recall (and this is going back some time) Candelas are a measure of luminous intensity where Sr (Steradian - three dimensional degrees) must be figured in. So a Candla is a Lumen per Steradian Where as a Lumen is the total quantity of radiated light. Basically they are not both measures of Luminous intensity - one is a measure of Luminous flux and the other a measure of Luminous intensity. For example if you take a 40 watt light bulb (approximatly 500 lumens - lm) and measure it's candelas based on its dispersion let's say about 75 candelas now you physically focus the light produced by the 40 watt bulb into a very narrow intense beam, it's candelas will jump but its lumens will remain the same. I.e. the amount of light the bulb produces will be the same but if focused narrowly enough you will not be able to look directly at the beam - it will be too intense.

This site has many light conversions but you will notice that Lumens and Candela appear in two seperate conversion windows. I have seen the formula you have posted but it only applies (not 100% sure about this) if the Steradians of the light sources are equal - this is rarely the case so it is sort of a rough conversion assuming similar styled radiators.

http://www.onlineconversion.com/light.htm

Anyway - just some additional thoughts.
 
Thanks for the correction ;)

okay, back to my array of 100 12000 mcd led's. That would be roughly 1200 candela. Comparable to a bulb of decent wattage...

I'm thinking that this could be interesting in a long strip... Well, i still have to do some testing. So amybe I'll get to this over the summer. Although this feels more like a winter project.


Jim
 
hey mad,
just ordered some 4000mcd blue led's for my moon light project. just a bit curious where you got your 6000mcd at and how much were they ? the 4000mcd are pretty bright, 2 of them make a perfect night light :lol:.

last week, i read on some website of a technique that can be used to increase the lighting angle. i haven't tried it yet, doing that tomorrow, so don't blame me for ruining an led.
the process involes using a dremel or low rpm grinding/cutting instrument, and grinding the bulb portion of the led down, to just above the metal parts inside the led. it should only take about 15seks, and after it's finished the light pattern that's emmitted should be a bit wider.

i am trying it tomorrow (too late now to try it) so, i will post the outcome good or bad tomorrow sometime.
 
as long as you don't touch the metal portion of the led it shouldn't be a problem. Look close though, there is a small wire in there. the ones i used in my nightlight were only 2600 mcd and they were plenty. I haven't seen any above 4000. The 4k ones were from lsdiodes.com and the 2600 were from radioshack.


Jim
 
i got my 4000mcd from there too, side note: they now offer 12000mcd (12k) white leds for 90cents a peice. i have seen 6000mcd back in college, but back then i was more worried about finishing labs and not experimenting (my priorities were all screwed up..) the Instuctor of the class bought a few hundred online and was giving them to other teachers, and playing with them.. they are very bright, lite up the classroom when the lights were off.
 
Hey Jprox,

Cjeck this site out for 4000 mcd blues, 6000 mcd greens and also 12,000 mcd whites - really cheap, shipped fast and the "company" (I think it's really someones basement :) ) seems really reliable:

http://www.lsdiodes.com/


Also: What I did to diffuse the light, was cut a 1" piece of 1/2" PVC, capped them on one side, drilled a hole in the cap to fit the LED snuggly facing into the pipe, then cut a small 1/2" diameter piece of plastic milk carton material and glued it to the other side. Voila - a mini-diffused LED spot light. I made three of these and mounted on a small strip - tested it last night on one of my fresh water tanks - worked great. I was a bit concerned how it would affect the fishes behavior - but all was well. They wouldn't swim anywhere near it for a while then one of them swam right into the center of the spot and sort of hovered there for quite some time - seemed like he thought he was basking in the moonligh :)

Before you go LED grinding :) you also may want to take a look at these LED condoms:

http://ledmuseum.home.att.net/whitecap.htm

HTH

Tom
 
My LED's are naturally diffused. Since they are only an inch or so from the water they have been powdered by saltcreep. I couldn't have planned it any better.


Jim
 
lol mad, that's where i ordered my blue 4000mcd from. i ordered wensday got on saturday. They are a good company fast processing, good shipping. Yeah it is ran out of some one's basement, if you look on the 'about us' portion, it says 2 college kids started the company because they didn't want to spend 4bucks on 1 led at a certain shack of radios.... :roll: so they started wholesaling leds. now both are at college and some people run the site and process the orders.

i just finished the grinding, and i have some mixed results. the lighting angle was minimally enlarged (maybe 10% if i was luckly) and the led was verry diffused.
so i don't know if grinding was a success or a failure. the light was so diffused it
hardly generated a beam when compared to a stock led. i tried poshling the led to restore some of the beam, but that didn't help, and i ended up going a little to far and destroyed the led. i order 10 (+1 free) so i have about another 5 more to play with. i will keep you guys posted.

diffusing: coat the tip of the led, in hot glue or aquarium sealer. if you feel it's to diffused you simply cut off a little of the sealer/glue till you get the satisfied results. and yeah salt creep is the ultimate diffusing substance.
 
wow, excellent prices on that site. Some of the LEDs must be atleast 1/4 the price at other places such as jameco.com and digikey.com

If you want to increase viewing angle and decrease the intensity why not just use a lense?

Grinding is not the best idea even if you can polish it up you will still probably leave "scars" that are bad enough to cause a great deal of internal reflection losing much of the light.
 
yep i learned that the hard way, about a week ago i stumbled onto some moding webpage, and there was an article on modding something, but in the article, they said by grinding you can increase the lighting angle, and if you order 10 from lsdiodes they give you an 1 free, so i experimented on that one and i have learned that it only increases the angle slightly, but it destorys most of the output. should have known that before i started, but it was just an led.. so no real big loss.
 
Jprox - did you see my earlier post - let me reiterate one point and add a new one I just tested:

1.) Check the LED condoms site on my earlier post. From what I've heard, these are excellent diffusers that just snap ontop of the LED.

2.) This afternoons project: I used a 1/2" PVC endcap, drilled a hole to accept the LED, Bought some fine prism panes (for flour. lights), 2' x 2' sheet from Home Depot ($2.79), cut a small 3/4" disc of this stuff and glued it onto the open end of the PVC end-cap. It worked great - pleanty of light but diffused. :)

I'm more pleased with the results of the fine prismatic plastic from Home Depot then the cut plastic from a milk container.

Glad you experimented on the free one and not one you paid for :)

Tom
 
Mad- i did check out the site,those condoms are used a lot in cars, esp japanese ones. today, i wanted to see what would exactly happen to the led. i was hoping it would get a little brighter, and the angle would increase but it didn't work and it was a great waste of 3mins, and about 45 cents. and sorry about the experiment sentence, i was just trying to be a little humorous but i doubt it came off that way.:wink:

but today i was just looking for something to do, and the advice sounded tempting so i gave it a whirl. your diffusing system sounds rather nice, i will be visiting my local HD and check of the panes. Thanks for advice
 
Hi Jprox,

On the experiment thing - yeah I knew you were joking - I was joking back :)

Yeah - my new difuser works really good - the only problem is that that stuff is hard to cut - be careful with it.

Caio

Tom
 
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