When using my new Energizer pivot torch i noticed that it dims itself slowly over 15 minutes from the start, reaching 1/10 of the maximum intensity. The torch does this on purpose and can be reset by turning it off and on again.
The HD vision headlamp
This lamp is probably my most used torch in my life. Even though I got it about 8 years ago for caving, it saw most action as a general headlamp around the house and clocked the most hours as a running lamp. It’s bright, but i am not sure what version this is, since Energizer make and has made probably 100 models of such lamps. You can grab one (probably newer version) from my affiliate link here.
I use it with rechargeable batteries which makes it slightly dimmer, but it is bright enough for running and various other work. I generally dump the batteries in the charger after each run, though I am sure the batteries are still rather full.
The lamp is controlled by an integrated circuit named IQS712 made by the same company Azoteq written on the PCB, but I cannot find a datasheet for it.
There are 5 LED lamps, 2 white for the wide field, 1 for the far field and 2 red ones. For running I use all 3 white LEDs, for illumination both close to me and far away.
Unlike the Energizer pivot which I just tested, this one is not regulated: the LEDs are driven from the battery with resistors and there is no DC/DC converter to stabilize it as the batteries get discharged. As such, the light goes dimmer as the batteries discharge.
Light it up!
This one has a similar approach to the other one, but a bit different. The light starts at maximum and stays bright for 15 minutes, then it starts dimming down over the course of 30 minutes to about 40% of the maximum value. So, it dims down 2.5 times, unlike the Energizer pivot which dims down 10X. Like with the other torch, the dimming is apparent also because of the flickering of the PWM.
There are 3 cycles in the figure there and I left the last one run till the battery went dead, for a total of about 8 hours until it started dropping significantly. As the battery discharges the light gets dimmer and each cycle starts at a lower maximum. The test is ran using both the wide and the narrow beam turned on at the same time.
Here is another 2 runs with the torch supplied from a lab power supply (3.9V). During the first 15 minutes when the lamp operates at maximum intensity the current drawn is 0.42A.
Note, the distance to the sensor is smaller now, this is why the peaks have a higher maximum.
Varta head torch HD30
But wait, there is more: I have another head lamp in my home, the this is the Varta HD30, also used for running and other tasks. This one claims 120 lm and 10hours and 2 x 1W LEDs. It has 3 LEDs, one red, one white for wide beam and one for narrow beam. A particular difference is that this one cannot turn both the narrow and the wide beam on at the same time, you have to choose and it also has a blinking mode.
The electronics insides are similar: there is a small microcontroller, this time a labelled one – a PIC12F510, transistors and resistors for the LEDs. There is no DC/DC converter so the light is also unregulated.
Light it up!
The test above is with rechargeable batteries. There are 3 start cycles. There is a similar behaviour to the energizer pivot: starts bright, and slowly and steadily dims down to about 30% of the max over the course of 20 minutes.
Conclusion & philosophy
The Energizer pivot and the two headlamps, the Energizer HD Vision and the Varta HD30, all dim themselves on purpose to increase the battery life. This way, the manufacturer can claim both a very bright torch (high lumens) and a long lasting battery and put 2 big numbers on the package. Now, since the lights can be dimmed down and get a much longer battery life, there is also usually a much longer duration specified on the package as well.
I checked the manufacturer’s website for all 3 torches (or similar models) and they never specify anything about the light dimming. Of course, based on the graph above the light will not last 4hours at the maximum intensity, but more like 2 hours with rechargeable batteries.
I don’t like that the manufacturers are doing this and find it hard to understand why they are doing it. Probably just to exagerate the battery life and make it sound better than it is. I would feel much better if the light really ran for just a couple of hours at max brightness, or however the batteries last this way. Since he light is dimmable, the user has full control of where to set the brightness and get anywhere between a few to many hours. There is also some argument to be made for thermal management, but I think both of the headlamps are barely pushing about 1W to the LEDs, so there is sufficient cooling. Not sure about the Energizer pivot though, as that one is pushing 3-4W to the LED.
Of course, knowing the lights do this, I can manually bring it back to max intensity when needed. But I would prefer if the product was more honest and did not do this dimming. The headlamps are a bit better, since they only dim down to 30/40 %, while the pivot work lamp dims down to 10%.