Fenix L2D RB100 light modes

So, I'm a giant noob to this scene and right now I've got a Fenix L2T. But I was also wanting to pick up the L2D Rebel 100.

My question is that from what I can infer from fenix-store, if you want 100/175 lumen output modes the light will be in SOS/Strobe mode. I'm hoping I'm interpreting the page wrong and that you can either use a constant beam @175lumen OR 175@strobe.

If the highest output with a constant beam is 50lumens, then I would just get the L2T Rebel 80 for a constant higher output.

Thanks!

In the turbo mode, you can have either 175 lumens constant or 175 lumens strobe. Both settings are available in the turbo level. In the regular levels it is low, med, hi, sos. The normal levels to the turbo mode is accessed by a twist of the bezel. To change from one setting to the next..ie. lo, med, hi, sos is a soft press of the switch. Same in the turbo mode. From 175 lumens constant to 175 lumens strobe and back is a soft press of the switch. To turn completely on or off in either mode is a full press/click of the switch.

BTW....Welcome to CPF

thanks for your help! thats what I wanted to hear.

Six modes in total. With the head tightly twisted you get Off, and powers on in Turbo mode. A brief click of the button and you get Strobe mode. A brief click again and you are back to Turbo. If you loosen the head a 1/4 turn you get Off, to low mode (note it may flash briefly high before going into low mode), a brief click and you get medium mode, a brief click and high mode, brief click and SOS mode, Brief click and back to low mode.

Now I think your question in the other thread hinted at the flickering you can see in some LED lights when the light is in a lower output mode. This is where they pulse the LED at maybe 60, 100, 1000, or more times per second. When the light is pulsed like this you tend not to notice in the high power modes but the low modes you do as the light may be on for only 5 of those 60 cycles in a second. Moving the light around and it becomes even more noticeable. Obviously the faster the flicker rate the less you will notice it.

The Fenix does NOT flicker the light unless you are in Strobe or SOS mode. Also the Fenix has a very efficient power circuit, even more efficient then the pulsed lights I have seen. (Based on selfbuilts battery testing.)

I don't know for sure, but I assume the L2D and other lights with multiple output levels use Pulse Width Modulation. ie. The led is pulsed at some frequency, 100Hz, for example, and the duty cycle of the pulse is adjusted to dim the light. ie. At 100Hz PWM, 90% duty cycle, the led is on for 9ms and off for 1ms, 100 times a second. The LED is actually flashing very fast and is on most of the time. Conversely the low mode might might be a 10% duty cycle.

Although many lights use PWM, the Fenix P3D, P2D, L1D, L2D do not. The LOD CE does. I do not know if the new L1T/L2T V2.0 lights do or not.

How do the Fenix D series vary the output level? You have sparked my curiosity.

I believe they are controlling the current to the LED. Less current, less output. BTW, PWM tends to get more efficient power usage out of LEDS, which is why a lot of manufacturers use it. I.e. at a 50% average brightness level out of the LED, PWM will use less power then current modulation. This assumes there is no loss in the circuit. Of course all circuits have some loss or efficiency rating.

Fenix actually gets better battery run times then comparable lights, even lights using PWM. It just shows that Fenix put some engineering into it and made a very good driver circuit. This is one difference of the Fenix quality.

PocketBeam said:

BTW, PWM tends to get more efficient power usage out of LEDS, which is why a lot of manufacturers use it. I.e. at a 50% average brightness level out of the LED, PWM will use less power then current modulation.

Click to expand...

Actually, I believe the opposite is true, LEDs are more efficent at lower currents, so a higher current (even pulsed) is less efficent. Incandescents may be the other way around though.

Yes, LEDs are more efficient at lower current levels (actually more middle current levels) and also at lower temps. Although, I am not sure there is a bid difference, seems the major reason PWM is used is to avoid the LED color shift when reducing the current to it. (Hm, I wonder if that is why Fenix doesn't have a lower low)

From - http://www2.whidbey.net/opto/LEDFAQ/The%20LED%20FAQ%20Pages.html[FONT=Arial,HELVETICA]Can I Increase LED Brightness by Using Pulsed Operation?

[/FONT][FONT=Arial,HELVETICA][FONT=Arial,HELVETICA]Compared to DC operation, it is sometimes possible to significantly increase visible LED brightness by pulsing. There are 3 reasons why pulsing can increase brightness: [/FONT][/FONT]
[FONT=Arial,HELVETICA][FONT=Arial,HELVETICA]1) LEDs have more output at lower temperatures. Low duty factor pulsing can, in some cases, lower the operating temperature of the LED.[/FONT][/FONT]
[FONT=Arial,HELVETICA][FONT=Arial,HELVETICA]2) The human visual system is non-linear. With the right choice of duty factor and pulse rate, perception will correspond more to the peak brightness than to the average brightness. This is especially true at low pulse repetition rates. However, there are a couple of potential problems with using low rep rates:[/FONT][/FONT]
[FONT=Arial,HELVETICA][FONT=Arial,HELVETICA]a) Visible LEDs may appear to flicker, especially at frequencies below 30 Hz.[/FONT][/FONT]
[FONT=Arial,HELVETICA][FONT=Arial,HELVETICA]b) Flickering sources may be a hazard to epileptics. For more information, see the following sources: [/FONT]:

British Epilepsy Association Photosensitivity Info

[FONT=Arial,HELVETICA] 3) Many LEDs have non-constant luminous efficiency. Luminous efficiency is the ratio of light output per milliamp of input. At very low and very high current levels, you get less light per milliamp than you do at intermediate currents. For an example of this phenomenon, see Figure 4 in the following Agilent (formerly HP) App Note:
[/FONT] [/FONT]
[FONT=Arial,HELVETICA][FONT=Arial,HELVETICA]http://literature.agilent.com/litweb/pdf/5091-9704E.pdf[/FONT][FONT=Arial,HELVETICA][/FONT][/FONT]
[FONT=Arial,HELVETICA][FONT=Arial,HELVETICA][FONT=Arial,HELVETICA]From the above considerations, we can make the following generalizations:[/FONT][/FONT][/FONT]
[FONT=Arial,HELVETICA][FONT=Arial,HELVETICA][FONT=Arial,HELVETICA]1) If you are trying to operate visible LEDs at maximum possible brightness levels, you will always get better results using DC operation. This is because luminous efficiency declines at high currents.[/FONT][/FONT][/FONT]
[FONT=Arial,HELVETICA][FONT=Arial,HELVETICA][FONT=Arial,HELVETICA]2) If you are trying to achieve a compromise between battery life and LED output, i.e., you are not operating the LED at maximum power, pulsing is probably advantageous. If the LED datasheet does not provide an efficiency curve, you will have to experiment to find the best compromise.[/FONT][/FONT][/FONT]

PocketBeam said:

...seems the major reason PWM is used is to avoid the LED color shift when reducing the current to it.

Click to expand...

Plausible, but I suspect the real reason why so many manufacturers use a PWM driver is because it is cheap.

Well cost could be the final factor some manufacturers use, as you have to have a analog control for current control.

I guess I should say I am not an expert on this...