I have an Exposure Diablo light. It runs for 1 hour at 900 Lumens & for 3 hours at 300 lumens. Is it possible to alter the internal settings to allow it to run for 2 hours at 600 lumens?
( the beam is good, but at 900 lumens does cause glare in our often wet miserable climate so with that in mind and to help make the light more usable, I thought 600 lumens at 2 hours would be a good compromise. Also I have very little knowledge of how these fancy lights work).
Many thanks
Dan
Dan.
Strike up a conversation with Exposure, tell them what you think as a customer and see if they might consider your comments.
As for adjusting an exposure light at the PCB level ?.
Not sure thats even possible.
After all, its Exposure's own set-up, etc.
I believe Lupine are releasing a twin LED, helmet compatible light.
Obvioulsy it will be stupid bucks, but its a que on where things might be heading.
personally could never see the point in the Diablo run time - I guess good for lap racing stuff, but I think the majority of riders would be looking for closer to 3 hrs for a 'normal ride'. yes you can run it on a lower setting and get that, but in that case a Joystick does the same and it's a bit lighter and cheaper.
Anyone know how to open up a Joystick? I need to replace my battery but don't want to pay 10x as much for exposure to do it... apologies for the thread hijack!
iainc- thanks for comments, however the spread of the light from the Diablo is broader and more usable than Joystick for mountain biking (and you can run the Diablo for 3hours at same lumen output as Joystick) and the 20grams extra in weight is no issue. and of course I've already bought the Diablo
Luminous- thanks for advice, I'll lift the phone now and ask them
bigdan6 - fair enough. 
If using as your main light I'd defiantely agree with you. I was meaning more as a helmet light to back up bar lights.
Hope you manage to get a fix, cheers. Iain
I've got a diablo and I reckon a "middle" setting between the current 900 and 300 would be quite nice as well, but just to be petty I'd still want the low setting as well (for a "dipping substitute" when on the road).
Being pedantic though, if you could somehow get it to run at 600 lumens, you'd get 1 1/2 hours, not 2. (half as long as 300 lumens).
I think the OP (and iainc) is making the error of assuming that if the light is rated at 900lmn for 1hr that the 3hr setting will be 300lmn. The relationship between light output (using LEDs driven with PWM - pulse width modulation) and power requirement and the relationship between power output and battery longevity are not not linear but exponential. This means the diablo reprogrammed to 2hrs would produce more than 600lmn of light. It also means that the 3 leds in a diablo discharging the same amount of power out of the single battery cell as the joystick will generate more light than the joystick's single LED (i.e. the diablo's 3hr setting is more iluminating than the joystick's 3hr setting).
I did talk Exposure about the concept of a user programmable light to determine what the 3 settings would equate to in term of output and power consumption when Rory Hitchins was still there and he felt the market was not ready for it as a product in terms of complexity and it might hurt sales as riders currently are in the habit of buying multiple lights for different scenarios.
OK, seems I may have been talking poo about run times in my post then. Oops.
I'm sure the Exposure blurb quotes 300 lumens for the 3 hour setting on the Diablo though (but I can't find anything to back that up now, so I may well be imagining that as well 
).
Given that the diablo is running at 100% PWM giving 900lm for one hour, would halving the PWM to 50% not result in twice the battery life and half the light then?
It "may" result in half the battery life but quite a bit more than half the light. Having said that battery capacity is not as simple as one might think. If you draw the power at a greater rate you also reduce the capacity available eg a battery might be able to provide 1 amp current(its optimal discharge rate in this example) for 12 hours making it a 12 amp hour battery (1a X 12hr = 12ah)but if you were to ramp the current to 3amps it might run out after just 3 hours giving it an apparent capacity of 9 amp hours (3a X 3hr = 9ah). Batteries' capacity are always rated at their optimal discharge rate.
I very much doubt the diablo is working at 100% pwm at max power however as there is very little discernible difference between 90% pwm and 100% pwm in terms of light output and it would be a waste of battery capacity.
Totally agree on the optimal discharge rate for batteries.
By "discernible difference" do you mean to the Mk1 eyeball or to appropriate test gear? I would agree to the former but probably not to the latter. I'd have to look at some of my results to make sure though.
MK1 eye ball - but I bet the difference with a modern LED if properly measured would be less than 1%.
I was working on a project using arrays of RGB LEDs (red,green,blue) this summer to generate an infinitely variable colour but also user variable (through a micro controller) intensity and volume. Getting the colour is a piece of cake (eg a certain shade of pink at a particular intensity and volume might be achieved with 30% pwm red and 60%pwm blue) - the problem comes when you want to change the volume as just halving both the red and blue does not result in a low volume of the same pink but a different hue because of this problem with the exponential relationship between PWM and light output. You have to use a rather complex formula to alter the PWM if you want to get linear change and therefore a constant colour. Sadly the exponential rate for each colour even on the same LED is different and needs a different formula.
Interesting. Are you sure that the colour shift you experienced wasn't a result of a reduction in LED junction temperature as you were driving them at a lower level?
probably has an effect too.
Something else for the mix (kick me if I am boring you). Typically for the LEDs which I have used, there is a 30% spread of luminous flux output for a given flux output bin code. So, driving sample A at 100% may result in 30% more light than sample B even though they have the same flux bin code.
We had that in the arrays we were using - not all producing the same hue for the same pwm details due to differences in the flux output for the different colours for neighbouring LEDs.
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