Diode Array System

Help with an LED array?

I'm working on an LED array, and I need to figure out how big a current-limiting resistor I need. I have the Shockley diode equation and I figured I'd just use that with Ohm's law and solve the system of equations, but I can't figure out the reverse bias saturation current, I have an equation for it, but it requires a number of values I don't have access to. I'd just use one of the online calculators to figure out my resistance values, but I need more detailed information to build the circuit safely. I only have 1/2 W resistors, and the fewer I cook the happier I am. Anybody have an easier solution? Some way I can make an estimate, average values for different sizes and colors?

Shockley equation is no help here.

You have to look the specification for each LED for Vf, and add them together (assuming they are in series) and calculate the resistor voltage by subtracting the sums of the Vfs for the LEDs, and use the LEd current with the resistor voltage to get the resistance.

If you don't have the Vf, get the part number and look it up online. Or find some similar one and use that Vf

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Types of Lasers for Hair Removal - Choosing the Right One

There are many different types of lasers used in laser hair removal. Each one caters to different skin and hair types. Your doctor should be able to tell you which laser is best for you. However, in the meantime, here are some helpful guidelines.

Listed below are some of the most common laser types and their wavelength. Several wavelengths of laser energy have been used for hair removal, from visible light to near-infrared radiation. The wavelength is measured in nanometers (nm).

* Argon: 488 or 514.5 nm
* Ruby: 694 nm
* Alexandrite: 755 nm
* Pulsed diode array: 810 nm
* Nd:YAG: 1064 nm

These different wavelengths have allowed people with a variety of skin types to have successful experiences with laser hair removal.

Pulsewidth is also an important consideration. It has been observed in some published studies that longer pulsewidths are safer in darker skin.

Wavelength is another critical factor. Longer wavelengths are safer in darker skin.

Spot size, or the width of the laser beam, affects treatment. Theoretically, the width of the ideal beam is about four times as wide as the target is deep. Most lasers have a round spot about the size of your little finger (8-10 mm).

By now, you might be wondering if this procedure is painful. Well, I can't lie to you, there is some pain involved. However, for most people it is extremely tolerable. Most people compare it to being snapped by rubber bands.

Fortunately, there are many methods of easing the pain. Epidermal cooling has been determined to allow higher fluences and reduce pain and side effects, especially in darker skin. Four types of cooling systems have been developed:

* Clear gel: usually chilled
* Contact cooling: through a window cooled by circulating water
* Cryogen spray: immediately before/after the laser pulse
* Air cooling: forced cold air at -34 degrees C (Zimmer Cryo 5 unit)

Make sure that your clinic employs some time of cooling system. If needed, your doctor can also give you some topical anasthetic.

You will need multiple treatments for optimal results. Multiple treatments have been shown in numerous studies to be more effective for long-term reduction of hair. Current parameters suggest a series of treatments spaced at 1 month for the face, 2 months for the chest and 3 months for the legs.

Look for a clinic that has a highly experienced and caring staff. With the right guidance and treatments, you could soon be on your way to smooth skin.

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