## Step 5: Electricity

Only a 3 battery and UV led are needed to demonstrate a simple electrical circuit. A resistor will be necessary for higher voltage batteries like the 9 volt battery shown here.
• Students can learn the difference between conductors and insulators.
• They can experiment using a pencil mark on paper as a variable resistor to dim and brighten the LED.
• Aluminum foil can be used to fashion a simple switch.
The possibilities are endless.

<p>&quot;at approximately 390 to 400 nm...UV LEDs will NOT make you go blind ...will not give you skin cancer either. UV LEDs are completely safe&quot;</p><p>But how do we know they are not ALSO emitting longer, dangerous wavelengths?</p>
<p>It is all about physics. The same laws of physics that make LEDs light up also limit their maximum wavelength range to a narrow band about 30nm wide. The range for most LEDs is even more narrow than that at less than 10nm. At 390 to 400 nm these LEDs are a long ways from the dangerous 10 to 315nm range. You have nothing to worry about with these LEDs. </p>
<p>Suggestion? Mention that UV LEDs are also outside of the range of the &quot;blue light hazard&quot; (which is centered around 440nm, I think, which is well above the wavelength of UV LEDs... Though there ARE a lot of high-power blue LEDs that will cause objects to fluoresce just like a UV LED and that ARE a &quot;blue light hazard&quot;, so I guess the guideline would need to be clear about that. Anyhow, just a thought. I am a big fan of LEDs!!! I also don't want to endure macular degeneration any sooner than I must, and I understand that UV LEDs won't encourage it (isn't it weird, though, that a light of longer wavelength than most purple &quot;UV LEDs&quot; is actually dangerous but then light starts becoming non-dangerous again after the blue portion of the spectrum has been passed? </p>
Impressive. I didn't know these many applications for the LEDs.thanks for the info.
awsome
good one on LEDs...
There are actually germicidal UV LED's on the market now (in the \$300/unit range) and those can burn and blind you. They are around ~250nm most commonly and are being tested and used for disinfecting water and surfaces. There are also UV florescent lamps that are germicidal as well but only special order, anything you find in a hobby or pet store is safe. In a few years (maybe less) the ~250nm UV LED's will be much cheaper and common in the marketplace so something to keep in mind.
Excellent presentation!
everyone into led's should reat this ible'. good work. I would like to add an observation. I was messing around with white led one day and put a voltmeter on one and hit it with light from another white. it produced a voltage, don't recall the exact voltage, but i think it did same in full sun too. been some time since then. since it's a pn junction, i would expect something like this. anyway, good work!
I found that out as well with white LEDs. I was checking if a LED could detect small amount of light but just thought it was my digital voltmeter acting up again as it sometime registers a voltage when the meters not connected. still reads correct voltages tho. <br> <br>Some of the items on the last list i didn't know about. great 'ibble

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Bio: After a career in industrial electronics I went back to college and now do DNA research.
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