Why does my JUNK key chain flashlight work so well?

Hello All! First post.

I searched the forum, but did not find what I was looking for, so:

Me: Mechanical Engineer with only basic knowledge of simple circuits and electrical tech.

We are building a small flashlight like device which is a manufacturing aid. We have been using a incandescent midget flange 3150 bulb in our design, but It does not have the light output needed. The device is too dim.

The device is continuity switched and battery power. Currently our design uses either the 11A or 4LR44. Both are small 6V batteries.

All the LED direct replacement bulbs we have found for the 3150 are also too dim. So we are looking at some design changes.

While looking at options I grabbed several small CHEAP JUNK key chain flashlights and shined them into our device and WOW, now that's perfect! It made our device VERY bright. So, I took them apart.

What I found confused me. I thought LEDs needed to have drive circuitry, not just a bulb. But, these small cheap key chain flash lights (five different ones) had nothing but bulbs and batteries. They had batteries configured in series to provide 6V driving 1, 2, or 3 LED bulbs. No resistors, chips, heat sinks, etc. This is similar to what I have

Then I said OK, just order some LEDS from Newark and do some testing. BUT when I go to order 5mm LED bulbs they have very little in 6V? uh? and nothing that is a bulb like what came out of the junky lights. What is going on? Are the junky flashlight over driving (with voltage) some 2 or 3 volts LED bulbs? Why don't they burn out? They are Sooooo bright! (compared to the 3150) Some of these junky light have been around my shop for several years and they worked great until I took them apart

So I need a little help to understand why my cheap junk light work so good and some help selecting a range a LED bulbs for bench testing.

Thanks a lot,
CD

These use little batteries, probably 2 disk CR2016s. Those do have 6v nominal voltage, but under the modest current draw of the LED, their voltage output drops. This balances pretty well with the LED's own current-voltage curve, giving decent light output with minimal risk of problems.

You have a few options: A substantial 6v power source with an appropriate resistor, using tiny batteries (That will dim over time and need replaced), or cutting a decent LED flashlight into your manufacturing aid. Those should be simpler than rolling your own device.

Edit: For a guess, a 3v 'wall wart' supply will probably work pretty well with the LED. If you notice the LED getting warm, it is much too overdriven and should get its power cut back. You can put a small resistor in series with the LED to do this.

OK, I will do some bench testing and report back. I appreciate the guidance!
Have a great day!
CD