If a light manufacturer is being more realistic they will advertise runtimes down to 1/2 of the max lumen rating not all the way until it actually quits.
It a light doesn't have a constant current driver (in which case it will be at max brightness until it just suddenly quits) it will only be at it's max advertised lumen output for a short while. As the battery is used the output will decrease. It may be advertised as 200 lumen for instance but after running for 1/2 hour it may be 170.
After using it for several dives it may now only be 100 lumens. When it gets so the battery is only able to produce 1/2 max lumen this should be considered its effective runtime. Maybe that's 6 hours (depends on the batteries).
If a light is advertised as running for days that's somewhat misleading. Sure it is still burning but it may not be any brighter than a candle. It's also something any nonrechargeable battery will do when powering led's. Led's are very efficient at lower power so it's a long, long time before the light actually doesn't come on at all.
However, if you buy a light that is advertised at 200 lumens and that is claimed to run for days and days you might think that means that it's running at 200 lumen for days and days...it's not.
Another fact is that there are only so many led's out there. Most lights, regardless of the sales prices, are using some of the same led's as other much cheaper lights. The actual retail cost of most led's is in the $15 range so the difference between a $700 light and a $50 light isn't the led.
It may be the build quality (higher production/test/development costs) or it may be looks or status or marketing but it's not the parts. You can find an expensive light that isn't well made and you can find a cheap light that is. Of course your chances are probably improved with a more expensive light but there is no direct correlation.
One other fact not always appreciated is that two lights with differing lumen outputs can appear to be the same at first glance. You may think that the higher lumen light must be the one that appears to be brighter. That's not necessarily the case.
The higher lumen model is producing more light but it may not be any brighter at the hotspot than a lesser lumen model with a tighter hotspot and no spill. Lumen is just describing the output. Lux is the measurement at a particular spot.
A 100 w bulb in the ceiling of the living room of your house may produce more lumen than the 60 w bulb that is by your chair that you use as a reading lamp. The light falling on your book from that 60 w bulb is brighter than the light falling on that book from the bulb in your ceiling.
Lights that need to be twisted to work underwater may be preferred as they are simple with no complicated parts involved or they may not be preferred because they can come on by themselves at increasing pressure. They also rely on o-rings to handle the dynamic motion of being twisted at pressure.
Magnetic switches have the advantage of not penetrating the body at all (and can't be a cause of leakage) and don't put any dynamic stress on sealing o-rings. They are more complicated and need to be well designed to keep magnets from falling out or if not sealed by degrading in saltwater. The circuitry internal to the light is more complicated and expensive although once properly designed is not so much of a problem unless the light leaks.
Non-rechargeable batteries have the advantage of lasting longer and rechargeable batteries have the advantage of saving money, being able to produce higher power for shorter periods of time with the right drivers and therefore allow for matching power to anticipated dive times.
Also, there is a limit to the use of non-rechargeables for higher powered lights. Or rather there is a useful limit. If a 1500 lumen light can only burn for 30 minutes that's not a useful dive light. If it can produce 1500 lumen for only a minute or two but burn for 2 hours at a rapidly declining level of output then that isn't really a 1500 lumen light either.
Led's are more efficient as power is reduced so with multiple power settings on a dive light battery power can be extended by reducing power on those dives when it's not needed. Since led's are more efficient as power is reduced this also means that a 50% reduction in power may only reduce the brightness by 35% so this can be a real benefit.
I see some misconceptions sometimes regarding led lights and that's the reason for this post. It's long and maybe isn't effective because of that but maybe it will help someone.
Anyone knowledgeable regarding led lighting feel free to clear up other misconceptions. Too much of a buyers knowledge regarding led lights frequently comes only from manufacturers' ads. This can be misleading.
It a light doesn't have a constant current driver (in which case it will be at max brightness until it just suddenly quits) it will only be at it's max advertised lumen output for a short while. As the battery is used the output will decrease. It may be advertised as 200 lumen for instance but after running for 1/2 hour it may be 170.
After using it for several dives it may now only be 100 lumens. When it gets so the battery is only able to produce 1/2 max lumen this should be considered its effective runtime. Maybe that's 6 hours (depends on the batteries).
If a light is advertised as running for days that's somewhat misleading. Sure it is still burning but it may not be any brighter than a candle. It's also something any nonrechargeable battery will do when powering led's. Led's are very efficient at lower power so it's a long, long time before the light actually doesn't come on at all.
However, if you buy a light that is advertised at 200 lumens and that is claimed to run for days and days you might think that means that it's running at 200 lumen for days and days...it's not.
Another fact is that there are only so many led's out there. Most lights, regardless of the sales prices, are using some of the same led's as other much cheaper lights. The actual retail cost of most led's is in the $15 range so the difference between a $700 light and a $50 light isn't the led.
It may be the build quality (higher production/test/development costs) or it may be looks or status or marketing but it's not the parts. You can find an expensive light that isn't well made and you can find a cheap light that is. Of course your chances are probably improved with a more expensive light but there is no direct correlation.
One other fact not always appreciated is that two lights with differing lumen outputs can appear to be the same at first glance. You may think that the higher lumen light must be the one that appears to be brighter. That's not necessarily the case.
The higher lumen model is producing more light but it may not be any brighter at the hotspot than a lesser lumen model with a tighter hotspot and no spill. Lumen is just describing the output. Lux is the measurement at a particular spot.
A 100 w bulb in the ceiling of the living room of your house may produce more lumen than the 60 w bulb that is by your chair that you use as a reading lamp. The light falling on your book from that 60 w bulb is brighter than the light falling on that book from the bulb in your ceiling.
Lights that need to be twisted to work underwater may be preferred as they are simple with no complicated parts involved or they may not be preferred because they can come on by themselves at increasing pressure. They also rely on o-rings to handle the dynamic motion of being twisted at pressure.
Magnetic switches have the advantage of not penetrating the body at all (and can't be a cause of leakage) and don't put any dynamic stress on sealing o-rings. They are more complicated and need to be well designed to keep magnets from falling out or if not sealed by degrading in saltwater. The circuitry internal to the light is more complicated and expensive although once properly designed is not so much of a problem unless the light leaks.
Non-rechargeable batteries have the advantage of lasting longer and rechargeable batteries have the advantage of saving money, being able to produce higher power for shorter periods of time with the right drivers and therefore allow for matching power to anticipated dive times.
Also, there is a limit to the use of non-rechargeables for higher powered lights. Or rather there is a useful limit. If a 1500 lumen light can only burn for 30 minutes that's not a useful dive light. If it can produce 1500 lumen for only a minute or two but burn for 2 hours at a rapidly declining level of output then that isn't really a 1500 lumen light either.
Led's are more efficient as power is reduced so with multiple power settings on a dive light battery power can be extended by reducing power on those dives when it's not needed. Since led's are more efficient as power is reduced this also means that a 50% reduction in power may only reduce the brightness by 35% so this can be a real benefit.
I see some misconceptions sometimes regarding led lights and that's the reason for this post. It's long and maybe isn't effective because of that but maybe it will help someone.
Anyone knowledgeable regarding led lighting feel free to clear up other misconceptions. Too much of a buyers knowledge regarding led lights frequently comes only from manufacturers' ads. This can be misleading.
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