What’s the suitable lighting modes of flashlights?

XTAR Light

Well-known member
Apr 26, 2010
Someone asked the question, “Why doesn’t Biscotti have a mode of 50%, 75%, 100%, or staggering between 50% and 100%?”. About the flashlights’ output mode setting, you maybe also think about this question before. Actually, there are something about the current, lumen output and perceived brightness.

As for current and lumen, they are not scale perfectly linearly. If you drive LEDs harder, they get less efficient. Take a look at this power input/lumen chart from Djozz below. From the XP-G2 output curve, in purple shows this difference. At 2.5A (50% of a 5A driver for the example), it tests at 900 lumens. At 3.75A/75%, it’s about 1150 lumens. At 5A/100%, it’s about 1320 lumens. So doubling the current, from 2.5A from 5A, there is extra 420 lumens of output, not an additional 900 lumens, if they are scale perfectly linearly.

For perceived brightness, it’s very nonlinear with the amount of light emitted. And The perceived light intensity is proportional to the square root of lumen output. So if you double the lumens, the light is only intensified by a factor of square root 2 or 1.41 times as bright. With 4 times the output, the light will appear twice as bright to the eyes.

Take the above example, going from 50% to 75%, only increase about 28% more output, and going from 75% to 100% at 5A only nets about 15% more light output, but not enough to be visibly different to the eyes. In order to get decent lighting efficiency and extended runtime with decreasing batteries’ current draw, the mode can’t be set arbitrarily between 50% and 100% in the beginning question asked. The level groups may space more logarithmically, and it makes the increase in brightness between each step seem evenly spaced apart.