Very Basic Flashlight Question

[gcbryan]

Can someone confirm that this is how a flashlight works at it's most basic level...

bulb/led in contact with the battery which is in contact with the tail cap spring and then side of the metal housing which completes the circuit back up to the bulb/led?

I know it's simple but I want to make sure I understand how it's all connected.

When I take off the tail cap I can make the led light up by touching the bottom of the battery with something metal as long as that piece of metal is also touching the housing. Is that what the tail cap spring is for to touch the battery and the housing?

For my last question, is it possible to find a small led flashlight that does not have a clicky switch but rather is a twisty only (and therefore potentially suited for underwater modification purposes)? I'm talking about twisty tail cap not twisty head.

Thanks.

 

[Gunner12]

The most basic flashlight is bulb connected to battery in a circuit. For an incan it doesn't matter if the battery is backwards or forwards.

LEDs are more complex. The simplest LED lights can be like the above description, but that will not always work. For example, a white LED needs around 2.5v to just light up, for usable output, you'll need over 3v. A single AA battery is 1.5v, which isn't enough to light up the LED, so there is a circuit called a boost circuit that raises the voltage from the power source (battery) to what the LED needs. These drivers also regulate the current going to the LED. If the batter's voltage is above the voltage of the LED, then a buck circuit is used to lower the voltage. Some circuits can buck and boost. Search for boost circuit or buck circuit to get more details.

When the light has different modes, it can be more complex. The simplest is to have a two stage switch, one with a resistor for a lower output. The more complex is to have a micro processor or something to change the drive current or PWM on-off cycle to lower the output or create the flashing modes like strobe.

LEDs also only pass current when the current flow is in the correct direction. They are diodes and that is a property of them.

The spring is for a good contact between the battery and whatever is used to pass current to the bulb/LED/driver. Most of the time it is the body that passes the current, but not always.

There are many twistie lights but most are bezel twisting lights. Are you searching for one that has an end twistie instead of twisting the head? You can modify an end clickie to an end twistie. What size are you looking for?

 

[gcbryan]

For the light I'm currently playing around with it would need to be around 25mm diameter. The light is roughly 5 inches long. The important thing is to find an end cap or another similar light with a solid end cap.

I understand that I can simply put a clicky in the on position and then twist the end cap to shut it off and on after that. I want a solid end cap so that the light can be modified for underwater use.

I just don't like the lights that do this by twisting the light head.

Thanks for your response by the way.

The most basic flashlight is bulb connected to battery in a circuit. For an incan it doesn't matter if the battery is backwards or forwards.

LEDs are more complex. The simplest LED lights can be like the above description, but that will not always work. For example, a white LED needs around 2.5v to just light up, for usable output, you'll need over 3v. A single AA battery is 1.5v, which isn't enough to light up the LED, so there is a circuit called a boost circuit that raises the voltage from the power source (battery) to what the LED needs. These drivers also regulate the current going to the LED. If the batter's voltage is above the voltage of the LED, then a buck circuit is used to lower the voltage. Some circuits can buck and boost. Search for boost circuit or buck circuit to get more details.

When the light has different modes, it can be more complex. The simplest is to have a two stage switch, one with a resistor for a lower output. The more complex is to have a micro processor or something to change the drive current or PWM on-off cycle to lower the output or create the flashing modes like strobe.

LEDs also only pass current when the current flow is in the correct direction. They are diodes and that is a property of them.

The spring is for a good contact between the battery and whatever is used to pass current to the bulb/LED/driver. Most of the time it is the body that passes the current, but not always.

There are many twistie lights but most are bezel twisting lights. Are you searching for one that has an end twistie instead of twisting the head? You can modify an end clickie to an end twistie. What size are you looking for?

 

[Gunner12]

You can usually remove the clickie and in place a round piece of metal with epoxy or something so it's waterproof, then make or find a contact that will complete the circuit when you tighten the talicap.

What price are you looking at for the light?

 

[gcbryan]

This particular light is a Romisen RC-K4 from DX for $16.00. Other than the clicky it looks interesting and well made just as an inexpensive way to be a little more experience modifying lights for diving.

I'll have to think in terms of the modification you've suggested.

I unscrewed the head and thought I would be able to easily remove the reflector to see how watertight the lens was but although the reflector will freely turn in place it doesn't come out for some reason.

You can usually remove the clickie and in place a round piece of metal with epoxy or something so it's waterproof, then make or find a contact that will complete the circuit when you tighten the talicap.

What price are you looking at for the light?

 

[Gunner12]

There is a tailcap retaining ring that you can untwist to get to the switch.

I'm not sure about the reflector though.

 

[gcbryan]

Thanks, I can see what those two little punch indentations are for now. I am now able to get the switch out.

There is a tailcap retaining ring that you can untwist to get to the switch.

I'm not sure about the reflector though.