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By chance, I came across my childhood night light. Plugged it in and low and behold, 30+ years old, but it still works but the bulb is very dim. I decided a fun little project would be to replace bulb appropriately. It's a very simple light, just an opaque thick blue plastic dinosaur that is illuminated from behind with a bulb wired directly to plug. I have experience with some soldering and arduino work but have very little working knowledge of electricity in regards to voltage, watts, amperage and how they all play together.

The plug of the night light had a black plastic cap with specifications stating 1/3w - 125v (pictured). The actual assembly (pictured) has what I believe to be a 30k resistor with a 5% tolerance judging from the bands (orange, black, orange, gold) and a calculator website (can't post the link as already have two links in this post which is the max for less than 10 rep).

Covering Original Bulb

I went to Lowe's and figured it best to go with the lowest wattage I could find - a small 12v 10w halogen. I also picked up a 120v 2w LED but the housing is too big so that won't work regardless. And after reading up more about all of this that 12v halogen bulb won't do in a household plug either, correct?

Long story short, what's a good small bulb and resistor to solder to the plug to make this functional again? I suspect maybe a 1w LED bulb? Would that still be in an appropriate range for the current 30k resistor in place?

Thanks for any help and sorry I know this is pretty simple stuff I just don't want to set my house on fire.

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  • \$\begingroup\$ It is supposed to be very dim. You don't need to replace the bulb. \$\endgroup\$
    – JRE
    Apr 1 '17 at 6:38
  • \$\begingroup\$ Well would you say that filament is also supposed to be burned onto the glass too? At the very least, it seems that I could probably get some better light out of a clear bulb. I didn't say I wanted to turn it into a torch. But I want to replace a bulb that is obviously on the way out. If you are looking to help with that, excellent. \$\endgroup\$
    – jaxwithanx
    Apr 1 '17 at 6:51
  • \$\begingroup\$ The light is orange, right? \$\endgroup\$
    – gbarry
    Apr 1 '17 at 7:01
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    \$\begingroup\$ You won't find what you need in Lowe's. You'll need to go to an electronics shop and find a neon bulb. The resistor is probably fine. I've never seen a neon bulb that really quit unless it got broken. I'm sure they do die at some point, but I've never seen it happen. I have seen neon indicator lamps in 50 year old equipment that still worked. \$\endgroup\$
    – JRE
    Apr 1 '17 at 7:07
  • \$\begingroup\$ Just to be clear: that thing looks like a neon lamp, and you should replace it with same - and I don't think it really needs replacing. \$\endgroup\$
    – JRE
    Apr 1 '17 at 7:08
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A few things:

What you have there is a pigtail neon. They're not like regular filament bulbs. You've probably seen these as power indicators in old / cheap multiway power-strips.

You don't necessarily want to increase the power output too much with your own replacement, because that additional heat is trapped inside a sealed plastic enclosure.

A 12V lamp will be immediately cooked if you try to power it directly off mains. Your intuition is correct. 10W is also an enormous amount of heat to produce in a sealed enclosure.

The topology of circuit you may be interested in can be found here. The capacitor acts like a resistor to drop voltage, but relies on reactance instead of resistance to do this ( no / minimal heat generated )

That'll mean the power rating of your LED will be the only heat produced in your circuit, more-or-less.

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  • \$\begingroup\$ Thanks for the confirmation and additional information. I realized that little 10w I bought was for a much lower voltage system after I got home. So replacing with a 1w LED would be potentially do-able due to the limited heat increase? Sorry if I'm misunderstanding. \$\endgroup\$
    – jaxwithanx
    Apr 1 '17 at 7:22
  • \$\begingroup\$ You could put in a 1W LED, but not without the additional work of building a capacitor dropper circuit or some other mains LED driver. \$\endgroup\$
    – Michael
    Apr 1 '17 at 8:51
  • \$\begingroup\$ @jaxwithanx If you want to use a LED check out this recent post. electronics.stackexchange.com/questions/295817/… \$\endgroup\$
    – Trevor_G
    Apr 1 '17 at 16:50
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    \$\begingroup\$ @Trevor Hey I really appreciate you pointing me there! So it looks like if I grab a 5mm 20mA LED, a diode (radioshack.com/products/1n4004-micro-1-amp-diode), and a 46k resistor I should have required pieces. This is my first time ever looking at schematics so I'm trying to piece this together. Is this scheme (imgur.com/RfJFKdD) and the scheme you posted (circuitlab.com/editor/#?id=265gm65yzn5k) essentially the same thing? Just want to make sure I'm reading things right. Essentially running a diode between after the resistor? \$\endgroup\$
    – jaxwithanx
    Apr 1 '17 at 18:59
  • \$\begingroup\$ @jaxwithanx that is correct. The other diode just protects the LED during the other half cycle. \$\endgroup\$
    – Trevor_G
    Apr 1 '17 at 19:02
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Success. @Trevor took the time to listen to what I wanted to do and point me to additional resources at - LED Applications

Now, with any luck, I'll be able to pass down to a child...updated with an LED.

Dinosaur

Night light

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