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Nightstar Frequently Asked Questions

Features - Technical Information - Frequently Asked Questions - Home

Q: Can light output be made brighter by replacing the LED with an incandescent bulb?

A: An incandescent bulb is highly inefficient and requires 10 times more energy than an LED. The capacitor in NightStar can only power a filament light bulb for a few seconds. By comparison, the energy stored in a battery is great enough to power inefficient devices for several hours. However, when a batteryís energy is depleted, it either has to be discarded or recharged.

Rechargeable batteries require external and often costly charging devices. Additionally, energy capacity diminishes with each charge and after 25 to 50 recharges the battery is rendered useless. Besides being inefficient, an incandescent bulb also has a lifetime of only 500 hours and is extremely fragile. Quite frequently, a bulb will break before it burns out. Therefore, for reasons of energy efficiency and reliability, an LED is the logical choice for the NightStar flashlight.

Q: Can adding more LEDs increase the light output?

A: The ETS Cell within NightStar can power more than one LED, and with each LED added, the light output will increase. However, power consumption will also increase with each LED added to the system. Consequently, the duration of light output obtained from a fully charged capacitor will diminish, thereby requiring NightStar to be shaken more frequently. Adding more LEDs will also increase the cost of the device. Therefore, one LED was chosen in order to maximize the time between recharge cycles and to minimize the unit cost.

Q: Can a reflector be used to project more light?

A: An LED forwardly projects light in a narrow and well-defined cone of illumination. Placing a reflector behind an LED will contribute nothing to increasing light output since there is no light to reflect. Adding a reflector to NightStar would only increase the unit cost and complexity. However, by placing a precision lens at the appropriate point, light output from the LED can be effectively collected and collimated. The lens in NightStar was chosen specifically to maximize light projection. The lens also serves as a window, and due to its design it is able to withstand tremendous pressure. Therefore, with the use of one component, optimum light output and the ability to survive severe pressure environments is obtained.

Q: Can a larger capacitor be used to increase the time of useful light output?

A: Several capacitors were studied during the development of NightStar. NightStar currently uses a 1-Farad, 5.5V capacitor. A capacitor with an energy storage capability 3 times greater than this is also available (3.3-Farad, 5.5V). However, it would require 3 times longer to fully charge this capacitor. The 3.3. farad capacitor is also larger and would increase the size of the flashlight. We concluded that 30 seconds of shaking to obtain 5 minutes of useful light would be more marketable than a larger flashlight that would require 1.5 minutes of shaking to obtain 15 minutes of useful light.

Q: Can batteries be included in the design to allow for a longer, brighter light output?

A: A battery will power the LED in NightStar for several hours at itsí maximum light output (the same light output obtained when the capacitor is fully charged and the light is first turned on). Additionally, the ETS Cell in NightStar can be used to charge a battery as well as a capacitor. However, the energy storage capability of a battery is many times greater than the capacitor used in NightStar. Consequently, it would require thousands of shakes to recharge a battery using an ETS Cell. Also, because the lifetime of a rechargeable battery is rather limited, it would ultimately need to be replaced. Batteries also fail to work effectively in cold environments; capacitors do not suffer this problem. Adding a battery to NightStar would therefore weaken its design and marketability. One of the most unique and significant features of NightStar is that it will never need replacement parts or maintenance. The components within NightStar and their integrated design yield a product that can be relied upon to light the way in the most extreme conditions.

Q: How is the charging magnet reflected at either end of the flashlight?

A: Neodymium magnets are mounted at both ends of the flashlight and are oriented to repel the charging magnet. The magnetic repulsion recoil system smoothly decelerates and accelerates the charging magnet back through the coil without loss in mechanical energy. Consequently, the loss of energy due to friction is extremely small and is only the result of the cylindrically shaped nickel-plated charging magnet sliding through a polished tube. Kinetic energy is therefore efficiently coupled into electrical energy with almost no degradation to the system. Lasting performance is obtained with this design.

Q: Can the flashlight be made smaller or larger?

A: The ETS Cell that powers NightStar can be scaled up and down in size. A smaller NightStar prototype has been designed. It is 35% smaller, requires approximately 60 to 90 seconds of shaking to become fully charged and has a useful light output that lasts 5 minutes. When resources permit, the smaller prototype model will be released as a product.

Q: Why is the housing made from plastic?

A: The most important reason is that any type of metallic housing will prevent the charging magnet from moving effectively through the coil. This is due to free electron eddy currents being set up in the metal housing when the charging magnet travels through the barrel. Consequently, magnetic fields generated by the eddy currents in the housing oppose the magnetic field of the charging magnet. The faster the charging magnet tries to move, the stronger the opposing fields will be in the housing. Therefore, the charging magnet will never pass through the coil with enough speed to charge the energy storage capacitor.

The plastic housing is superior to a metal housing in several other ways as well. The material and manufacturing costs of plastic are far less expensive then aluminum (aluminum is a likely choice for a metal housing). Additionally, NightStarís plastic housing will never rust or oxidize and weighs less then an aluminum housing that would provide the same amount of crush resistance. The plastic used in NightStar is an alloy of polycarbonate and ABS (Clear NightStar however, is made of pure polycarbonate; polycarbonate/ABS is not available in clear). Polycarbonate/ABS was chosen for two reasons. First, it is difficult to break even at cold temperatures, and second, it is unaffected by salt water, mild acids, alcohol, methanol, ammonia based cleaners.

Q: How does the switch work?

A: Inside the switch is a small magnet. As the switch is moved forward the magnet slides over and activates a reed switch mounted on the circuit board inside the flashlight. When the reed switch is activated (or closed) energy in the capacitor flows through the LED. This design feature has several advantages over conventional mechanical switches used in other flashlights. The most significant advantage is reliability; the simple sliding plastic switch can not corrode or wear out and the reed switch is rated at over 1 million cycles. In comparison, mechanical push button or toggle switches have components that corrode and springs that fatigue after very few on/off cycles. Another key advantage to NightStarís switch design is that it does not require a watertight seal sense the magnet on the outside is able to active the reed switch through the plastic housing. Finally, because the electrical circuit is not exposed to the outside world (as with a typical mechanical switch) there is no possibility of igniting combustible materials.

Q: Is a pacemaker sensitive to the magnetic field that surrounds NightStar?

A: NightStar can affect a pacemakerís normal mode of operation. If the heart rate of a person with a pacemaker drops below a preset value (typically 85 beats per minute), an internal sensor monitoring the personís heart rate activates the pacemaker. A pacemaker will not send electrical signals to a personís heart unless their heart rate drops below the preset value. In order to test whether a pacemaker is operating properly, a reed switch is built into the unit so that an external magnet held up to the patientís chest will close the reed switch and deactivate the internal heart rate sensor. When this happens, the pacemaker turns on and begins sending electrical signals to the heart at the preset value. Pacemakers are typically tested once or twice per year in specially equipped hospitals. If a pacemaker begins sending signals to the heart at a rate of 85 beats per minute and the heart is already beating at a greater rate, an arrhythmia condition can be triggered. The possibility of this occurring is extremely rare; less than 1 percent of the people with pacemakers would be susceptible to this condition, and those that are, are in many cases already bed ridden. A magnetic field with strength of 90 gauss brought within 1.5 inches (40 cm) of a pacemaker will close the reed switch. The magnet in NightStar has a surface field strength of over 5200 gauss. Consequently, a person with a pacemaker should avoid holding NightStar any closer than 2 inches (5 cm) from their chest. At this distance the field strength has dropped to approximately 30 gauss.

A cautionary statement regarding the effect NightStar has on pacemakers is printed on the product packaging and instruction booklet. (This information was obtained from a phone conversation with one of the largest manufacturers of pacemakers in the U.S.)

Q: Can the flashlight be made with a beam focus mechanism?

A: A beam focus mechanism may be integrated into future models. It was not incorporated into NightStar because of a desire to reduce initial complexity and production costs.

Specific Component Information

  • Built inside NightStar are two 5.6-volt zener diodes, which protect both the LED and the capacitor from over voltage. In so doing, both components are insured to last their rated lifetimes.

  • A full bridge rectifier is used to transform the electrical energy generated as the magnet sweeps through the coil from Alternating Current (AC) to Direct Current (DC). The electrical energy is then stored in the capacitor.

  • The capacitor is a 1-farad double layer gold capacitor that can store a maximum of 12 joules of energy. [In comparison, a 1.5-volt battery can store approximately 5500 joules of energy]. It leaks off energy at a rate of 8 milli-joules per hour. The capacitor chosen and used in NightStar has two significant advantages over batteries. First, it can be charged and drained of energy over 1 million times. Second, it can operate in extreme temperatures. NightStar has been proven operational at a temperature as low as minus 130 degrees F and as high as 180 degrees F. The capacitor works well in this application because the LED is an extremely efficient device.

  • The LED is 70 to 80% efficient compared to an incandescent bulb, which is only 5 to 10 % efficient. Consequently, 70% of the electrical energy delivered to the diode by the capacitor is converted into light. The LED draws only 20 milli-amps of current and runs at a maximum of 5.6-volts, and is rated at over 100,000 hours of operation. It can run as high as 6 volts but this would begin damaging the LED and potentially shorten its lifetime. The electrical energy delivered to the diode from the capacitor results in the emission of high energy blue photons centered at approximately 400 nano-meters. These high-energy photons strike a phosphorus material fused inside the diode. This process generates a broad band emission of light spanning from 400 to 700 nano-meters. Its maximum light output is approximately 10 lumens.

  • The rare earth neodymium magnet used in NightStar has a core field strength of over 30 million gauss and a surface field strength of over 5200 gauss.

  • NightStarís unique contoured shape is an example of form following function. In order for NightStarís injection-molded components to consistently and precisely fit together, wall thickness must remain uniform across each part. The unique and flowing contour of NightStarís housing evolved as a consequence of this design requirement. Eliminating excess material adds the benefit of reducing both the unit weight and cost. NightStarís quality and lasting performance is therefore the result of optimizing function and form.



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