You only need to know that particular chemicals are used to produce each light colour plus basic info. presented in following sections. We'll also cover various types of LEDs and how they're used for festive lighting. Refer to Wikipedia for more info. http://en.wikipedia.org/wiki/Light-emitting_diode.
There are many LED types, sizes ( round 3, 5, 10mm diameter), colours, shapes, self flashing, brightness, angle of view, etc. - too many to cover! The LED's electronic symbol is a arrowhead with light beams as shown below. Note a plain arrowhead is used to show a LED in my diagrams.
Brightness
The brightness range of LEDs goes from candle power to a CIA interrogation light! So when buying your LED check the spec sheet with it. To use a LED's brightness, we have to go techy here with some basic units of light measurement which are:
- lumen is a measure of the total "amount" of visible light emitted by a source. (reference http://en.wikipedia.org/wiki/Lumen_(unit))
- candela is a power emitted by a light source in a particular direction, weighted by the luminosity function (reference http://en.wikipedia.org/wiki/Candela).
Since the light output from a LED is restricted to +- 20 degrees from centre, you could say lumens roughly equal candelas. Also 1000 milli candela (mcd) = 1 candela (cd); ditto lumens.
So LED brightness goes from 200mcd up to 290,000 mcd (multiple LED chips in one package) at rated current. You can briefly look directly at a 5000mcd LED - so this is optimum brightness for light displays in the night. However, if you use a brighter LED, you can reduce its brightness to about 5000mcd by reducing the current (ie use a higher value resistor) - the advantage is gained when you have 100's of LEDs which can use a smaller power supply! Another cool reason is the ability to do shimmering - the LED is switched at varying fast frequencies to make its brightness flicker very quickly.
Polarity
So LED brightness goes from 200mcd up to 290,000 mcd (multiple LED chips in one package) at rated current. You can briefly look directly at a 5000mcd LED - so this is optimum brightness for light displays in the night. However, if you use a brighter LED, you can reduce its brightness to about 5000mcd by reducing the current (ie use a higher value resistor) - the advantage is gained when you have 100's of LEDs which can use a smaller power supply! Another cool reason is the ability to do shimmering - the LED is switched at varying fast frequencies to make its brightness flicker very quickly.
Polarity
All LEDs are polarised devices just like a battery, ie correct connection gives light; incorrect can blow it up and there’s no light. It’s best to replace a LED which was energised in reverse polarity – it will usually work when correctly connected but it may fail quicker than a good LED.
I'll show you the polarity markers for each type of LED in the relevant post and how to check polarity - see below.
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| SMD type strip |
LED basic types for Christmas lights: surface mount (SMD) or with pins/ legs as shown.
Connection
DC Current must flow from the LED's anode to cathode (see sketch) to get light! This simply means connect positive to anode, negative to cathode (ignoring switches, resistors, etc) as shown in my circuits (link). Now for circuits using the LED symbol, current flow is in the same direction as the arrowhead.
Note do not connect a LED directly to AC - it goes banGG! Use a rectifier (see AC/DC section).
NEXT >> SMD LEDs
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