LED bulb for sextant .... anyone found a good one?

[Rowglide]

Hi I was tooling around with my sextant, and noticed that the light bulb is not working. I replaced it with the spare and all is well but I wonder if anyone has found a suitable LED replacement.
There are hundreds of 222 style screw in bulbs available online, but there are many different outputs. Rather than order a bunch and start experimenting, I thought I'd ask here in case someone has already found the right one.
My graduated arc is bronze (not very polished but shiny enough) if that matters.

Thanks
Jim

[Benz]

When my sextant bulb went out, I just started using a headlamp to read the arc. After all, I need the light to write down the reading. But I've also made ghetto compass lights by buying a 3-volt LED from Radio Shack, along with a 2AA battery holder. You could probably splice an LED like that right into the wires in the sextant handle, if one of the 222 bulbs doesn't work out.

[bletso]

Depends on your sextant model. I have an Astra IIIB before LED. I had been irritated by the short life span of the bulbs used in the Astra. I ask them if it could be upgraded to LED and they said no. Soooo, it took 15 minutes, a small LED, and a resistor to convert it. No more lights out in the series of shots!

[svHyLyte]

Originally Posted by bletso

Depends on your sextant model. I have an Astra IIIB before LED. I had been irritated by the short life span of the bulbs used in the Astra. I ask them if it could be upgraded to LED and they said no. Soooo, it took 15 minutes, a small LED, and a resistor to convert it. No more lights out in the series of shots!

Bletso--That is a very useful "upgrade". Do I assume correctly that you wired the resistor in series with the positive lead on the LED to reduce the battery voltage level to that the LED could accept? And, based on your snap, do I correctly assume you used a Blue LED or do I see the light as "blue-ish" simply from the nature of the color rendering of my monitor verses actual? (On our sextant the OEM light is white although red would seem to be a beeter alternative to preserve one's vision at twilight, no?)

[bletso]

No, it is blue, just my preference. Yes the resistor is in the battery compartment.
As sights are only taken in twilight colour is not a big concern. BTW, the long lead is the ground and you can see it in my original pic going to one of the screws.

[BobbieGWhiz]

Nice. Can you specify what size resistor and specific led you used. Thanks. (I’m not an electrician.)

[Rumrace]

A resistor will work and the LED will run about half life. Finding a couple Blue diodes worth owning challenging. 1.8 watt is typical and the 3 watt version will be slightly more consistent. You’ll need an eye piece but there actually are +&- markings. Reverse the polarity they blow instantly. The resistor can go at either end of the diode doesn’t matter. You need a 512 resistor for 1.8W 12V. What the diode really is suppose to get is 350mA and a pulse rate of 160htz or higher.
This is why professional LED systems have drivers or constant current transformers. The so called 12V LEDs have a soso driver (choke ballast) on their circuit board. This is what you’ll find in most marine products. Automotive experts like Toyota Mercedes Samsung know better and have steered the industry away from Chinese junk. I’d specifically look for a Phillips Holland diode 1watt

[Mirage35]

You can also get LEDs with required resistor in a single package - just hook up to the appropriate voltage and you're good.

This data sheet is for one I used in another project - may not be exactly what you're looking for but will give you the concept.

http://static.vcclite.com/files/5100Hrev1.pdf