Flasher - How to detect loss of brightness

[burpee]

How would you go about detecting the effective run time of light configured as a "flasher" or blink mode?

If you know how much current/voltage (watts) the light will draw when being lit with a full battery, -would you conclude that the "flash" must be dimmer when you have drawn the battery down 33%?

For instance, if you have a three watt light in flash mode, but the battery is now down to supplying only two watts - can you assume the "flash" must have dimmed ~33% (or about a third) as well?

Thank for comments or links to additional material.

 

[Selectron]

If the manufacturer of either the light or the driver released a detailed datasheet then the information might be found on there, but in the absence of that then the only practical way to determine run-time in blink mode would be to measure the on/off time durations using an oscilloscope, either directly by tapping into the circuit, or via a photo-sensitive interface. Easy if you have a 'scope, but difficult otherwise.

Assuming a comparatively negligible current is consumed by the driver circuit during the intervals between flashes, the effective run time in blink mode would depend on the duty cycle, i.e. the onff time ratio. As an example, if the light blinked once each second, with an On duration of 0.1 seconds and an Off duration of 0.9 seconds then the duty cycle would be 10%, so if a light had a one hour run-time in continuous mode then that would be extended to ten hours when in blink mode - assuming it was fed with the same current in both modes, but again that is something which would be revealed by an oscilloscope.

I can't speak for lithium cells because I don't use them, but with NiMH cells I would expect them to last somewhat longer in those circumstances because of the extended rest intervals between flashes - even apparently depleted NiMH cells recover usable capacity very quickly when allowed to rest, even if only briefly.

In the case of a direct drive light but with mode-module driver, the brightness in both continuous and blink modes would indeed dim as the battery gradually discharged, but that wouldn't necessarily be the case with other drive types - a good constant-current generator for example would be able to maintain a fairly constant brightness, but it would really depend on drive type and the efficiency of any particular circuit.