LED lights: A Few Facts

[gcbryan]

I agree that so called OTF lumen will always be lower than spec and that's why I said a MC-E at 700 lumens spec should be in the ballpark of the HID's 450 lumen after all the inefficiencies so it is correct to say that a led can be comparable to a 10W HID.

In fact I have a 10 W HID and a MC-E and took both on a night dive. I tested throw with one and then tried to see if the other could match it. I also measured the hotspot beam angle first with one and then with the other.

They both performed about the same. The MC-E had more spill with the same 6 degree hotspot so actually lit up a greater area than the 10 W HID.

I was just questioning the statement that a led couldn't have the same "punch" as a HID. I think at a certain point they can. Right now they're more in line with a 10W HID rather than a 21W HID although with the SST-90 if it can be properly focused I'm not sure that it's not comparable as well.

I do agree that the numbers with leds are a lot more nebulous than with HID given the binning system and due to heat issues.

 

[gcbryan]

delete

 

[Greg_Vic_Diver]

I was just questioning the statement that a led couldn't have the same "punch" as a HID. I think at a certain point they can. Right now they're more in line with a 10W HID rather than a 21W HID although with the SST-90 if it can be properly focused I'm not sure that it's not comparable as well.

The reason I said that is because manufacturers have overstated the performance, thereby making people think LEDs have less "punch" than HID. A lumen is a lumen (a cd is a cd)

 

[gcbryan]

The reason I said that is because manufacturers have overstated the performance, thereby making people think LEDs have less "punch" than HID. A lumen is a lumen (a cd is a cd)

Ah, thanks for clearing that up. I'm not being argumentative here. I just want to make sure we're clearing up issues rather than creating more.

I couldn't agree more that a lumen is a lumen and talking about HID's having some kind of magical "punch" is nonsense.

That's the biggest if not misunderstand then just not understanding regarding the issues involved in led lumens. A lumen is a lumen but with led's it's hard to pin down the actual lumens (if the manufacturers don't have them tested) due to the binning system, heat issues as well as the inefficiencies that would affect any light (optics, reflectors, drivers, etc).

 

[jaydil]

If a light manufacturer is being accurate they will advertise runtimes down to 1/2 of the battery power not all the way until it actually quits.

gcbryan, I applaud this call for standardized ratings.

However...this is the wrong metric.

What we really need is standardized runtimes down to 1/2 of the maximum lumen output. Also, the manufacturer must state exactly which battery chemistry & capacity they used for that measurement.

1/2 of battery power is not a useful metric. It is quite possible, for example, to have a light that puts out only 10% of rated lumens when the batteries are down to 50% power.

Quoting runtime in terms of time to 50% max light also encourages the manufacturers to be more realistic about their lumen ratings. For example, if a light spikes at 500 lumens for the first 30 seconds on fresh batteries, then drops to 400 lumens and declines slowly for the rest of its runtime, a 500-lumen rating will make the runtime look worse (because the cutoff is at 250 lumens instead of 200 lumens).

I think this thread is a great idea...but only if the first post is edited with technical corrections and additions. gcbryan, are you up to that?

Cheers-
J

 

[Greg_Vic_Diver]

What we really need is standardized runtimes down to 1/2 of the maximum lumen output. Also, the manufacturer must state exactly which battery chemistry & capacity they used for that measurement.
J

While I too applaud you both for trying, what I think would make the most sense is the runtime of the LED at the full rated brightness. 1/2 brightness and 1/2 capacity are just silly. It needs to be the "autonomy" or runtime of the lighting system at the desired brightness level until the light goes dimmer (-15% rated lumen output after the stablization period) than what is specified.

I am a customer. I would like to know how long my light will last at the desired brightness for which your light is rated for. I would like to see photmetric plots that show the light output intensity, beam divergence angles, lumens and chromaticity. I would also like to know how many cycles I should expect out of my battery before it degrades below 80% residual capacity (C/10 discharge test). enough said.

 

[jaydil]

Greg, you and I are basically saying the same thing, just with a different number.

85% of the lumen rating would be nice...but it doesn't account for useful regulated AND unregulated runtime. If you specify an 85% cutoff, a light that runs above 85% regulated for 1 hour and then goes dark within 5 minutes will look better, runtime wise, than a light that runs at 85% for 50 minutes, then drops out of regulation and slowly declines to 50% over 40 minutes. But the second light gives much more useful illumination, plus it's safer for diving because it degrades gracefully.

The 50% light output cutoff is a metric that many of the respected land-based flashlight manufacturers already use for runtime specs. Actually some dive lights do this too. I think I recall seeing this spec on the PT Torrent instruction sheet.

Plus, 50% makes more sense w.r.t. our real-world visual response. Our eyes do not respond linearly to light intensity. You have to drop the intensity by 50% to really notice a difference...and then it looks, subjectively, 10-20% dimmer.

I also want to see beam divergence and chromaticity specs, absolutely!!! Just tackling one issue at a time.

-Jeff

p.s. Battery cycles are much easier to estimate. You can usually pull your batteries, figure out who made them, and look up the datasheets. The flashlights provide much less information. You can't tell what flux/tint/Vf bin an LED comes from just by looking at it. Or look at the driver and guess what its output currents and efficiency might be.

 

[Greg_Vic_Diver]

Greg, you and I are basically saying the same thing, just with a different number.

85% of the lumen rating would be nice...but it doesn't account for useful regulated AND unregulated runtime. If you specify an 85% cutoff, a light that runs above 85% regulated for 1 hour and then goes dark within 5 minutes will look better, runtime wise, than a light that runs at 85% for 50 minutes, then drops out of regulation and slowly declines to 50% over 40 minutes. But the second light gives much more useful illumination, plus it's safer for diving because it degrades gracefully.

The 50% light output cutoff is a metric that many of the respected land-based flashlight manufacturers already use for runtime specs. Actually some dive lights do this too. I think I recall seeing this spec on the PT Torrent instruction sheet.

Plus, 50% makes more sense w.r.t. our real-world visual response. Our eyes do not respond linearly to light intensity. You have to drop the intensity by 50% to really notice a difference...and then it looks, subjectively, 10-20% dimmer.

I also want to see beam divergence and chromaticity specs, absolutely!!! Just tackling one issue at a time.

-Jeff

p.s. Battery cycles are much easier to estimate. You can usually pull your batteries, figure out who made them, and look up the datasheets. The flashlights provide much less information. You can't tell what flux/tint/Vf bin an LED comes from just by looking at it. Or look at the driver and guess what its output currents and efficiency might be.

While your comments make sense when running on a direct drive or conventional halogen light, they make no sense for a DC DC converter driven LED drivers that run at a constant current. As the battery voltage drops, the current can stay constant. Our military and USCG customers would not accept a LED that would work at only 50% of the rated output, why should we as divers using this light for safety be any different?

I agree on your point about graceful degradation, just make sure I get my run time at the specified output first. You should be planning your dives around the useful run time of your light and doing load tests on your batteries to monitor capacity degradation. There should be no reason to need the graceful degradation.

 

[gcbryan]

I agree on your point about graceful degradation, just make sure I get my run time at the specified output first. You should be planning your dives around the useful run time of your light and doing load tests on your batteries to monitor capacity degradation. There should be no reason to need the graceful degradation.

Let's try to keep this thread on point which is to discuss the facts regarding lights that others who haven't been as interested in lights may not be aware of.

There is a place for graceful degradation. It can be useful in a backup light. You're free to disagree or to have other preferences but it's not a fact that there is no place for it. Again, there is a useful place for unregulated as well as regulated lights. Anything beyond that is opinion or preference.

Also, it's good that changes to industry standards have been brought up as well but again let's not make this thread primarily a debate about that.

I think everyone has provided valuable contributions to help clear up some confusions in this subject matter.

 

[gcbryan]

I agree on your point about graceful degradation, just make sure I get my run time at the specified output first. You should be planning your dives around the useful run time of your light and doing load tests on your batteries to monitor capacity degradation. There should be no reason to need the graceful degradation.

Let's try to keep this thread on point which is to discuss the facts regarding lights that others who haven't been as interested in lights may not be aware of.

There is a place for graceful degradation. It can be useful in a backup light. You're free to disagree or to have other preferences but it's not a fact that there is no place for it. Again, there is a useful place for unregulated as well as regulated lights. Anything beyond that is opinion or preference.

Also, it's good that changes to industry standards have been brought up as well but again let's not make this thread primarily a debate about that.

I think everyone has provided valuable contributions to help clear up some confusions in this subject matter.