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I was wanting to get a bulk lot of small LED lights similar to Basic LED - 5mm Yellow. I want to put them in balloons so that the balloons appear to glow in a dark environment, so I have a few questions:

  1. Would the heat produced by these lights be likely to burst the balloons? I understand that most LEDs produce little to no heat.

  2. Is there a decent and inexpensive alternative that have a power supply "built in" or attached? (so we dont have wires running from the balloons). Failing this is there an alternative that just need a small battery to be connected?

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1) The LED would be fine and never produce enough heat to pop the balloon. 2) You could make them into LED throwies. Just a small coin cell batter and an LED.

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You could make LED floaties, just an LED taped to a CR2032 3V Lithium coin cell, put inside the balloon before filling it with helium. Supposedly they stay lit 1-2 weeks. The internal resistance of the battery limits the current.

enter image description here

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    \$\begingroup\$ Nice answer if that link dies... \$\endgroup\$ May 2 '12 at 13:06
  • \$\begingroup\$ @FedericoRusso: Thanks, I complain about that all the time now when other people do it. :) \$\endgroup\$
    – endolith
    May 2 '12 at 15:11
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Don't forget the resistor! If you add a resistor, it will last for much longer on a single battery, and is less likely to damage the LED.

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Depending on the type of LED, you may or may not need a resistor in a throwie configuration.

I wrote up an article examining some of the subtleties involved in that question; you may want to take a look. (Spoiler: For red or yellow LEDs, DEFINITELY use a resistor.)

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For simplicity of construction, get an led that will work on a 3v button cell without a resistor. You can then make a "throwie" that can be constructed with just the led, battery and a bit of tape. It won't make much heat at all, the button cell will have enough internal resistance so it won't act like a short though the led.

The alternative is to cannibalize some Ethernet cabling or old printer cables. Run the cabling up the string or, alternatively, use the cable as the string itself. This means one controller board and power supply can drive the LEDs at the smallest current possible, making the least amount of heat. But really this is much more complicated, just stick some throwies in balloons and inflate them. The only prohibitive thing is the cost of the batteries.

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