Help Me With My LED Essay

Ken_McE

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Light Emitting Diodes (LEDs) For Illumination

LEDs used for illumination are available in many colors from visual Infrared, through the visible spectrum and into the near Ultraviolet. They are often listed as UV when they are really purple. It is hard to blame vendors for this as eBay lumps the two categories together. Most of these LEDs are made in China. Their color is very pure compared to incandescent bulbs. They can be turned on and off frequently without harming them, unlike fluorescent bulbs.


Millicandelas (mcd) are the unit of brightness most often cited in listings. Millicandelas are measured at a single point directly in front of of the LED. This is great if you only need a tiny point of light, but makes it difficult to meaningfully compare different LEDs. Lumens refer to the total amount of light put out by any light. Unfortunately most LED specifications do not list this measurement

You could for example, have one LED that emitted 10 lumens of light, but spread them over a 100 degree angle. If you put this next to a LED that only emits 1 lumen (one tenth as much light), but concentrates it into a 10 degree beam, both would have the same mcd rating.

LEDs are tiny little things that weigh almost nothing. extravagant shipping fees are standard. It is normal to pay $15 shipping for an order that could easily travel in a first class envelope.

Advantages

Physically small. Long life. 100,000 hours, or ten years, is a figure often given for half life. Any light will dim with time. LEDs tend to dim very slowly. They will last even longer and be even more efficient when under driven (run with less than full power). They are essentially immune to cold, shock, and vibration. They have low energy consumption. They turn on and off more quickly than incandescent bulbs, which is useful for brake lights.

Disadvantages:

The beam tends to be more directional than that of an incandescent bulb. They are sensitive to small variations in current. A small increase in current can drastically shorten their life expectancy. 3, 5, , and 10 mm LEDs won't melt themselves out from under snow like an incandescent bulb.

They have less "throw" than an incandescent bulb. They have a higher initial cost. There can be variation within and between batches. At this time they are not good for high output applications such as headlights and area lighting.

common sizes

* SMD (Surface Mount Device)

Little tiny LEDs too small for normal people to solder.

*3 mm
*5 mm
*10 mm

bullet shaped, number refers to diameter of LED in millimeters. Has two leads at the flat end of the bullet. Very common.

*Spider/Piranha

Flat square LEDs with four pins on the bottom. Usually have a wide beam. The extra legs give them extra mechanical stability.

*"High Power" LEDs These units need to have a heat sink or they will overheat and burn out.

1 watt
3 watt
5 watt


Automotive

Legality

resistance
 
Last edited:

magic79

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:goodjob:

I think you should retitle "Light Emitting Diodes (LEDs) for Illumination", since thousands-of-times as many LEDs are used for purposes other than illumination, and as such, your comments don't apply to those types of LEDs.

I PM'ed some edits for you.
 

Ken_McE

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Lurker said:
Are you planning on selling this essay on eBay?

No, not at all. It will be available without charge as a guide for potential buyers. I won't even know who looks at it.
 

greenLED

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Warning: Nothing personal, I am a brutal editor.

Some general advise:

* Who's going to be your audience? Write accordingly.
* If you're doing the selling, maybe think about your specific LED product, and choose the highlights of your product. No need to write a LED Encyclopedia if you're selling LED replacements for automobiles.


More specific comments:

Their color is very pure as compared with incandescent bulbs. They can be turned on and off frequently without harming them.
Not sure this would be clear to a non-CPF'er. "Pure color"?
Why does turning on/off frequently with no harm matter?

Lumens refer to the total amount of light put out by any light. Unfortunately most leds do not list this measurement. Millicandles are the unit of measurement most often cited in listings.
The unit is actually milicandela. The first two sentences are OK, but they don't help clarify anything. Start by stating LED's are commonly rated in milicandelas, then explain why that's not ideal.

It is normal to pay $15 shipping for an order that could easily travel in a first class envelope.
:thinking: Normal to pay $15 shipping? It's only $3.85 for a flat-rate Priority Mail box. There's lots of room in there for tons of padding. I don't think I've received a package of LED's that cost more than $2.50 (via First Class, and that's with proper padding). I walk away from ebay sellers who overcharge on shipping.

They will dim with time. 100,000 hours or ten years often stated for half life. They will last longer and be more efficient when under driven. Turn on and off more quickly than an incan. bulb.
How is dimming with time an advantage?
Again, why is rapid on/off important.

They are sensitive to small variations in current. A small increase in current can drastically shorten their life expectancy. They won't melt themselves out from under snow like an incandescent bulb.
The two first comments are great, but for someone unfamiliar with LED's... they might wonder what to make out of that. Why's not melting out of snow a bad thing? Seems very application-specific.
 
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Ken_McE

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Warning: Nothing personal, I am a brutal editor.

OUCH! BAM! BIFF!! Man that Greenled can swing!

greenLED said:
:thinking: Normal to pay $15 shipping? It's only $3.85 for a flat-rate Priority Mail box. There's lots of room in there for tons of padding. I don't think I've received a package of LED's that cost more than $2.50 (via First Class, and that's with proper padding). I walk away from ebay sellers who overcharge on shipping.

Heres an example:

http://cgi.ebay.com/50-PCS-Mega-Bri...yZ111608QQssPageNameZWDVWQQrdZ1QQcmdZViewItem

.99 for the item, $18.00 for the shipping.
 
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chesterqw

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the easily avaliable colours of LED which led (no pun intended) to no filter being use so there is less light loss.
 
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