Falchoon

So if one light battery is rated at 650 mAh and another at 600 mAh (both being Li-Ion rechargeable) then the one with the highest number is better?

The 600 mAh one is rated at 120 LM and the 600 mAh one is rated at only 90 LM. I know the more Lumens the better for (rear) light output.

The 650 mAh light has only 4 LEDs and the other has 16 LEDs.

The 90 LM/650 mAh one has an advertised run time of 4-8 hours (Hi > Lo > Flash) but the other one doesn't have a run time listed but has diffferent modes (Hi > Mid > Flash > Strobe). Charge time is claimed 3 hours for the 650 mAh one and 2 hours for the 600 mAh version.

Will I (or more importantly, motorists) notice a difference between 90 LM and 120 LM?

Are these claimed ratings accurate? Lights are cheap Asian ones so I'm thinking maybe not...

VegasTriker

It is hard to compare lights that use discrete LEDs because you often don't know what type of LED is used in the light. Some LEDs are more efficient than others so will give you more lumens or a longer run time with the same capacity battery. Don't be afraid to try the Asian lights since many of the US brands are simply Chinese lights made in Chinese light makers branded with a US seller's name. The Blitzu Gator 320 light I received as a Christmas gift was made by Raypal, one of the largest Chinese bike light makers. It is sold without the Blitzu name for about half the price. How far a bike tail light can be seen is partly dependent upon the brightness but also on the area of the light that is lit. That's why I prefer a COB tail light because the light is evenly spread over a decent area. I'll PM you with some suggestions for lights I own.

CliffordK

Also, keep in mind that mAh is a rating of amps over time. So, if you have two 4v batteries, one rated at 600 mAh, and the other at 650 mAh, then they may both have the same instantaneous power, and thus may have equal light intensities, but the one rated at 650 mAh will last longer (in theory). As far as long-term longevity, the rating doesn't mean a lot, although the higher Ah rating may mean it has a better buffer for a slow decline (or it could mean they took shortcuts, and the battery won't last as long).

Power = Watts = Volts x Amps (and power over time = watt hours).

So, if you have say a 4V battery, and an 8V battery pack with the same mAh rating, then the 8V pack will be able to put out more watts hours, and thus more overall power (over time).

The nice thing about rating in volts and Ah (1000 mAh = 1 Ah), is that it makes it easier to calculate the battery characteristics when building multi battery packs in serial and parallel. Serial connections increase volts, and parallel connections increase amps and amp hours.

Sal Bandini

mAh is like gas tank in your car. It measures capacity.

Car A has 10 gallon tank. Car B has 15 gallon tank. Which car is better? Like your 2 lights you are considering, it depends.

You will not like notice big difference between 90 and 120 lumens, that's assuming they are accurately marked, which they probably are not.

I don't know what bike you are riding but assuming it's a nicer model, spend the extra $20 or so for quality light. That's chump change compared to cost of bike.

fietsbob

Milli amp per hour is used to state battery capacity , but it can also be rate of drain by the demand end.

Iride01 

Think of battery capacity as the gallons your cars fuel tank holds. The bigger the tank the more miles or time you get.

But when comparing different lights, it's just like comparing different cars. Bigger engines usually require bigger tanks.

So if the light manufacturer doesn't give you a chart or tell you how long the light will last in different modes, you cannot really compare them.

Nor can you use the battery capacity to compare brightness. Lumens or the outdated term candlepower is for that.

There may be generalizations you can make, but just like with cars. Some high performance ones get amazingly good mileage and attract everyone's attention too.