This post goes out to my Chi Alpha pastor, who a few years ago at the end of a weekend conference said "The difference between a flashlight and a laser is focus. Right now, i need you to focus." Although his words had the desired effect, this is strictly speaking not true. A flashlight focused down to a millimeter spot is still a flashlight, and a laser diffused to a meter spot is still a laser. But it did get me thinking about modern humanity's various light sources and what kinds of qualities our Light in the world might have.
1. Incandescents: Here i include traditional filament light bulbs and well as other thermally stimulated light sources, such as candles. The point of an incandescent bulb is to dump so much heat into a small space that the normal infrared emission of all warm objects shifts up into the visible spectrum. Although they can be made quite intense with the right lenses and reflectors, incandescent bulbs are primarily a heat source. This model describes every youth group i have ever encountered. An enormous amount of energy goes in and the atmosphere inside is 'on fire'. This can sometimes be highly visible in the immediate environment but the effect is essentially random. Mostly what is apparent is excitement; the emitted light conveys very little about the bulb or the power source.
2. Fluorescents: Fluorescent bulbs contain a vapor (often mercury) which is electrically excited to emit ultraviolet light. This strikes a phosphorescent compound on the walls of the bulb to produce visible light. This isn't the most efficient process in the world; the activation current is quite large and the two-step process still generates a lot of heat. This mostly characterizes my adult, evangelical experience. The fluorescent understands that it is primarily a light bulb, not a self-heater, but it generally takes a decent kick to get the light going and the flickering can get pretty bad at times. The emitted light is more a function of what the bulb can make than what the bulb-maker wanted. Its only because the creator of the bulb knew how to absorb and re-emit that light that the bulb is effective at all.
3. Light-Emitting Diodes: LEDs are made from semiconductors with a gradient of impurities along their length. Impurities of different charge set up an internal electric field. When enough current is applied, this field collapses, letting electrons combine with empty electron sites, emitting light. LEDs are brighter and more consistent than fluorescents. They can also be switched on and off much faster and with less over-charging. Simple LEDs emit a single frequency of light; while this frequency is fixed for a given LED, it can be altered in the creation process. More sophisticated LEDs have a fluorescent material built in which spreads out the emitted spectrum to produce 'white' light. Many Christians i know strive to be more like LEDs, quick to respond when called, bright, effective and durable.
4. Lasers: Light Amplification by Stimulated Emission of Radiation. To make a laser, place a light-emitting material ('gain medium') between two mirrors and add power. The gain medium will try to emit light in all sorts of frequencies and directions. But rather than emit directly to the outside world, this light is bounced around internally. At first almost all of the emitted light is re-absorbed, feeding back into the power source, but light that is of the right frequency is amplified on each pass. Over time the light bouncing around the laser cavity becomes more and more what it was designed to emit, all the same wavelength, direction and phase. One of the mirrors is usually partially transparent, letting the intense beam of coherent light out into the world. While it is true that lasers are supremely focusable, their defining characteristic is coherence, which is achieved by letting the laser cavity prune away photons that don't match the mission of the laser. The difference between a flashlight and a laser is not focus, but submission to the power source.
