LEDs The LED (light emitting diode) is an electronic device that can be very useful for a number of theatrical tasks. They don't require large amounts of power, emit practically no heat, and can be seen from relatively long distances. The LED does not have a limited life. An LED will essentially last as long as the current (ma) limitations are not exceeded or they are mechanically destroyed. They can work well as cue lights, spike marks, and spotting lights for dancers (in some cases). There are, I'm sure other uses that I haven't mentioned. The most common LED is red in color. There are also green and yellow LEDs as well as LEDs that can produce all three colors depending on how the power is applied to it. An LED can easily be operated from a pair of 1 1/2 volt AAA batteries (3 volts) for a period of time(hours). An LED is a diode that emits light. It has essentially no resistance of its own, so if it is connected directly to a battery it will burn out quickly. A resistor must be wired in series with the LED to limit the voltage drop across the LED to approximately 2 volts and at the same time limit the amperage passing through the diode to less that 30 to 40 milliamps depending on the particular LED used. One quarter or one eighth watt resistor are of sufficient size for the currents used. Here is a list of typical values: Supply Resistor Amperage LED Voltage (volts DC)(ohms) (ma) Drop (volts) 3 10 40 2.4 (brighter) 3 100 10 2.0 3 150 6.7 1.9 (dimmer) 5 150 17 2.2 10 330 23 2.1 12 680 14 2.0 The value of the resistor can be varied somewhat to increase or decrease the brightness. Alternately the voltage can be dimmed up or down within reason. An LED is a polarized device. This means that current will only pass through it in one direction. If it is connected backwards nothing will happen, it simply will not work. Most LEDs are manufactured with one lead (wire) longer than the other. The longer one, the cathode, is connected to the positive terminal of the power supply or battery. There is also a flat area on the plastic on the cathode side of the device. The negative connection is called the anode. It doesn't matter to which wire the resistor is connected as long as it is in series. Each LED must have it's own resistor. Multiple LED/resistor pairs can be connected parallel to each other at the power supply. Care should be used in assuring that the total amperage of the LEDs does not exceed the output capability of the power supply. If many LEDs are connected to a battery it may go dead in less time than desired. Simply multiply the total number of LEDs by the amperage of one LED/resistor pair to determine the total amperage required of the power supply. (Note: 1000 milliamp (ma) equals one amp). A power supply is the better source of voltage if the LED(s) are illuminated for an extended period of time. A good, easy, and relatively inexpensive power supply is one of the "battery eliminator" power supplies used with many types of portable entertainment equipment. Radio Shack and similar stores have several to choose from in a variety of voltage and amperage ranges. Now for some uses... The LED can make an excellent spotting light for dancers or even actors in situations were they must find their bearing with no apparent light. The LED is so light in weight and requires so little current that it can be taped to a surface, or even the window of the booth, and a very small pair of wires run a substantial distance to the power supply. In a like situation, a number of leds can be placed across the front edge of the stage angled upstage and masked so that the audience can't see them. They are very bright when viewed straight on but don't cast ghost light very far. They can be recessed flush into an angled strip of wood so that they only project in one direction. In this case, it might be necessary to increase the value of the resistor to decrease the brightness if it is objectionable. Safety backstage can be enhanced by placing them along stairways. These can be recessed into the step so as to be out of the way. These LEDs can replace standard running lights in some situations were the standard light produces an objectionable glow. LED's placed in holes in platforms can make great spike marks. There can be a separate set for each scene The sets can be be switched on one at a time as needed. These could replace glow tape as a placement device. They are visible in total darkness and the brightness can be regulated. As a cue light, 2 or 3 LEDs switched separately could be used for warning, standby, and go. Another possibility is to use a special dual-color LED. These are red when a DC voltage is applied in one direction and green when the DC voltage is reversed. Another type, the tri-color does this plus yellow when an AC voltage is applied. Led's are also useful as indicator lights to monitor special effects and machinery devices. This is more complex so I won't go into it in this article. I've detailed a number of ways that LEDs can be used on the stage. I'm sure you can think of others. They are inexpensive and easy to use. One thing though, solder the connections; the wires are small and somewhat delicate. They can be pulled apart quite easily if not firmly attached. The wires should be placed where they are not likely to be snagged by scenery, costumes, or people.