Have you seen them? They look like a normal flashlight, but are very different: they charge themselves, they don't use batteries, and their bulbs never burn out. Shake flashlights have been extremely popular over the past few years as an emergency kit part, and they work great, but there are a few things you should know about them before you run out and get one.
A traditional shake flashlight has the following attributes:
Completely sealed & waterproof
LED bulb that never burns out
Magnet & coil charging system
No battery
Capacitor for storing the flashlight's power
Being completely sealed & waterproof is an obvious benefit. Especially in emergency & survival situations, you want equipment that is tough, and won't fail when the going gets tough. Water has an ability to get past seals & caps, so it is better when electronics come completely sealed. Not even high humidity will affect a good shake flashlight.
LED bulbs are different than normal lightbulbs. LEDs are a semiconductor device, like a transistor is, that emits light when electricity is put through them. They come in different colors & powers, but the best part is that most can operate for more than 60,000 hours before they stop working. If you do the math, this amounts to almost 7 years if you were able to keep it 'on' the whole time. If you only use the flashlight for 2 hours a day, this means it will last you longer than 70 years! The other nice thing about LEDs is that they do not have a filament or glass bulb, and therefore are extremely tough & will take a drop.
The magnet & coil charging system is very unique. There are lots of dynamo flashlights that use a handle to turn a dynamo generator that charges the flashlight, but a shake flashlight uses a magnet sliding through a coil instead. Why? Well, it is very tough to make the flashlight completely sealed & waterproof with a handle sticking out of the body. The sliding magnet approach does not charge as quickly as the dynamo, but they are simple, and tough.
No battery? Yes, that's right. A REAL shake flashlight does not use a battery, not even a rechargeable. Why? Because batteries will eventually fail, and the whole idea of a shake flashlight is that it will never fail. Not to mention that a completely sealed & waterproof body makes it tough to replace. NiMh & NiCd batteries like to be used, and do not like to be left uncharged, so having an emergency flashlight with these batteries is not always a good idea.
So, if a shakelight doesn't use batteries, then how does it store power to run the LED?
The answer is its "capacitor".
A capacitor is another electronic component commonly used in radios & TVs that temporarily holds power. They come in a range of sizes, and shake flashlight use what is called an ultra-capacitor that holds quite a large amount. The best thing about capacitors is that they do not have a finite lifespan. Most of them will never lose the ability to store a charge, making them a far better choice for use in a sealed, & long-life shake flashlight. The only problem with capacitors is that they discharge faster than batteries, so you will see that the flashlight loses brightness faster with a capacitor than a battery.
Are all shake flashlights the same?
No.
I have seen many shake flashlights that cut corners to save cost. The result is a reduction in performance & lifespan, which ignores the very reason for building a shake flashlight in the first place. Sometimes these are marketed as 'Hybrid' flashlights, and sometimes they do not even tell you what's inside. Modern Outpost has seen dozens of models, and have taken some of the cheaper models apart to find secret lithium batteries that boost performance for the first few hours only, or an NiMh battery that is subject to failure. Remove these batteries, and these cheap knock-offs stink in terms of performance.
If you want a renewable energy flashlight that is brighter & cheaper, then look into the dynamo wind-up models that use multiple LED's. If you want a completely waterproof self-powered flashlight that will last for decades, and provides enough light to get you through emergency situations, then the true shake flashlights are the right ones for you.
Popular real shake flashlight models include...
ShakeLight:60 by Generation Gear
Nightstar by AIT
