• Welcome to ScubaBoard

  1. Welcome to ScubaBoard, the world's largest scuba diving community. Registration is not required to read the forums, but we encourage you to join. Joining has its benefits and enables you to participate in the discussions.

    Benefits of registering include

    • Ability to post and comment on topics and discussions.
    • A Free photo gallery to share your dive photos with the world.
    • You can make this box go away

    Joining is quick and easy. Login or Register now by clicking on the button

LED lights: A Few Facts

Discussion in 'Lights' started by gcbryan, Feb 1, 2010.

  1. gcbryan

    gcbryan One Bad Hombre

    # of Dives: 1,000 - 2,499
    Location: Seattle
    15,975
    9,918
    113
    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.
     
    Last edited: Feb 1, 2010
  2. lucca brassi

    lucca brassi Photographer

    # of Dives: I'm a Fish!
    Location: Kocevje , Slovenia , Europe
    1,225
    110
    63
    That's why standards exists - problem it is that manufacturers (of (diving) lamps as final product - not LED's as semiconductor ) are not quite forced to follow standards (or standards are not determined ) .
    some standards
    or something like LBNL
    It is also problem that manufacturer have it's own standards and they follow them - but they are not comparable between producers in generally.

    ( something completly different as for example : breathing regulators ,scuba tanks which they have very rigorous regulations )
     
    thirdcoastdiver likes this.
  3. wquiles

    wquiles Nassau Grouper

    79
    0
    0
    Great post :)

    Another member and I were also having a discussion on the subject of testing:
    http://www.scubaboard.com/forums/lights/321249-lumen-output-diverite-led-lux.html


    Some sites do independent testing of lights, this one being one of the best (in my opinion) as they use a fairly consistent method and rating scheme, although I don't recall them having an Integrating Sphere:
    Flashlight Reviews and LED Modifications


    Here is another one:
    Flashlight Reviews, Torchlight Reviews, LED, HID, Xenon & More


    And of course our own flashlight forum has a section for members to share their own reviews:
    Flashlight Reviews - CandlePowerForums


    Of course most sites will not be "diving" specific, but it still helps to see how different lights/brands are rated.

    Until such a time in which manufacturers are forced to follow some guidelines, and undergo some uniform testing, I don't see this mis-communication ending any time soon.

    Will
     
  4. gcbryan

    gcbryan One Bad Hombre

    # of Dives: 1,000 - 2,499
    Location: Seattle
    15,975
    9,918
    113
    Thanks for the additional links guys.

    As the both of you know once someone becomes more interested/knowledgeable about how lights work regarding emitters/drivers/voltage and amp requirements you can read between the lines somewhat regarding dive light manufacturer ad copy. Since not everyone is that interested I thought this thread might be helpful.

    I saw that thread Will regarding the Dive Rite Lux and that addresses the standards issue which would help sort out this mess.

    The other aspect though isn't manufacturer related but rather just being more knowledgeable about the issues I raised above namely understanding which light characteristics are appropriate for which diving conditions as far as direct drive vs constant current vs rechargeable, beam angle, lens, power, etc.

    In the mean time I guess just becoming a little better informed is the solution.
     
  5. wquiles

    wquiles Nassau Grouper

    79
    0
    0
    Absolutely - well said. Just making potential buyers more knowledgeable means that we can be better prepared to ask more intelligent questions, instead of just taking marketing material at face value.

    I recently created a thread on how to modify lights, and although it is biased with my own/personal point of view, this thread has some potentially usable information. The part on estimating runtimes is one of those that is pretty universal for any/all lights, so I will link it here in case anyone cares to take a look: link ...

    If you feel this detracts from the initial intent of your thread, please let me know and I will edit and remove the link. No worries either way.

    Will
     
  6. gcbryan

    gcbryan One Bad Hombre

    # of Dives: 1,000 - 2,499
    Location: Seattle
    15,975
    9,918
    113
    Not at all Will. I remember seeing your thread a while back...excellent thread!

    I think anyone would benefit from being able to do a quick rundown of the numbers for estimating runtime. I do it all the time when I see what emitter is being used and the battery supply to see if the claims are in the ballpark.

    If nothing else people will quit bragging about getting a 4.7W light over a 3 W light when they realize that's (potentially) like bragging about getting 20 mpg in their car instead of 30 mpg!
     
  7. Greg_Vic_Diver

    Greg_Vic_Diver Divemaster

    # of Dives: I'm a Fish!
    Location: Canada
    125
    14
    18
    I work at a company that designs LED luminaires and LED drivers. We have a full photometric test tunnel here for aiding in the design and quality assurance of our products. I do not see the same commitment from dive light manufacturers OR their suppliers.

    I see the word "lumen" being used incorrectly. Folks, lumens is the total sum of light (corrected for the human eye response) emitted from a source (in total) regardless of beam angle. A light CANNOT produce more lumens than the sum of its emitters.

    Lux is the lumens per square meter it is an intensity measurement at a point.

    There is some headway underway at the DOE to get manufacturers to start labeling LED products similar to the nutritional facts you see on food products: check out LightingFacts.com : The Lighting Facts Label

    This should solve the problems with LED lights such as DiveRite's LED Lux which has wayyy overstated its actual light output. See this thread for proof:
    What's the deal with the Diverite LED LUX? For real or not? - CandlePowerForums

    I have asked Diverite to make a statement about how they tested their light:
    http://www.scubaboard.com/forums/dive-rite/308949-led-lux-2.html

    It is up to us consumers to demand that LED lights have the correct ratings to allow an informed decision. An integrating sphere lumen test costs only a few hundred dollars and there are many labs that can do it. Demand a photometric plot from the manufacturer that has the information such as that in the lighting facts sheet. Do not buy products from those that will not provide this info.

    Ever wonder why you keep hearing how LED lights don't have the same "punch" as a HID? Well it's because they don't! Misstated specs make and accurate comparison impossible. A standard 10W HID will have about 500 lumens of light.

    As for battery power ratings, most LED product use what's called a buck converter. this will require the input voltage to the driver (battery voltage) to be around 2V more than the LEDs need. A battery may very well have the capacity to run longer, but if the voltage does not meet a minimum requirement the LED driver will not work. Ask if the run time is at full rated value and what % of deviation from the stated run time would be considered faulty.
     
  8. gcbryan

    gcbryan One Bad Hombre

    # of Dives: 1,000 - 2,499
    Location: Seattle
    15,975
    9,918
    113
    Thanks for your post by the way. Regarding this specific quote however I'm not sure what you are referring to. Do people frequently state or believe that a light CAN produce more lumen than the sum of it's emitters?
    Again, just to clear up this quote...for example a Welch Allen 10 W HID puts out 450 lumen and a Cree MC-E (quad) emitter puts out 700 or more lumen...this to me is roughly comparable to a 10 W HID.

    Are you saying that it isn't? They are different in that a HID has a pinpoint source of light and therefore there is a brighter pinpoint spot in a HID hotspot than a comparable led but output beam angles and lumen are comparable.

    Please clarify your point. Thanks.
     
  9. wquiles

    wquiles Nassau Grouper

    79
    0
    0
    Keep in mind that for all lights that use a reflector/optic and protecting lens that not all of the output generated by the bulb/filament or LED makes it out of the light - you always have some amount of loss. Not only that, those LED lumens are lumens measured in a special lab fixture, kept at (typically) 25C, but as the LED heats up the efficiency drops so the output drops, so on a real/actual light it can't possibly give this max/theoretical value.

    So, you have losses from the reflective/optics used, from the lens in front, and then from the "real" setup/heatsink. So even if the LED "could' in fact put out 700 or 800 lumens, the real output might be "significantly" less. So those theoretical 700 lumens might be more like 500-550 lumens, which would likely appear to be "roughly comparable" to the 10W HID.


    For incandescent lights is the same, in the forums we use "bulb" lumens vs. output lumens, and of course output lumens being always smaller than bulb lumens. Many folks in the forums have measured SureFire lights, and they have found that the lumen ratings are actually on the "conservative" side - a very rare thing for a manufacturer, yet again, Surefire has government/military contracts, so perhaps that is a factor here. In fact, if you look at the M6 here you will find they quote 250 and 500 lumens (the M6 ships with a low power and high power bulb), but the actual lumen value measured for this light is around 400 and 600 lumens :D

    Will
     
    Last edited: Feb 1, 2010
  10. Greg_Vic_Diver

    Greg_Vic_Diver Divemaster

    # of Dives: I'm a Fish!
    Location: Canada
    125
    14
    18
    Well, I'm not sure how many but I have definitely seen one in particular (check the links I provided above). LEDs have vastly different lumens output depending on the drive current.

    The bulb used in the DiveRite 10W HID is 500 lumens, and that is tested using calibrated equipment. I can send you a spec sheet if you are interested.
    When you see an LED light rated at 500 lumens by the manufacturer and it is actually only say 300 lumens if tested by calibrated optical test equipment then it is an unfair comparison. Lumens (cd is a lumen/steradian) takes into account the human eye response curve such as the CIE 1931 Candela - Wikipedia, the free encyclopedia

    If you can harvest the lumens through a collector (lens) you can make the light what ever shape you want. Keep in mind that optics have efficiencies as well and the more lenses the light passes through the more lumens are lost. Generally, the samller the optic the less efficient it is. If you had an HID lighting system with a FWHM of 6 degrees and a LED lighting system with a FWHM of 6 degrees they would be near identical if they both were actually 500 lumens.

    Notice I used the word "system”, we are measuring the actual output of the light from the system and not just the emitting source behind the lens.
     

Share This Page