Lumens with multiple LEDs?

I recently built a homemade headlamp using Luxeon I stars. They are rated at 45 lumens each at 300mA. My question is if the lumens are additive or not. In other words does my headlamp put out 3 x 45 = 135 lumens (# of LEDs multiplied by the lumens produced by each one).

The headlamp seems extremely bright to me but its my first experience with high power LEDs and anything beyond a stock mag light. In case your curious I built it based on the following http://www.instructables.com/id/Ultimate-Night-Vision-Headlamp---500+-lumens-with-/

I used the following circuit though with 3 LEDs in series and a high/low switch. http://www.instructables.com/id/E7QH8NG8I1EWOF32HJ/

Yes, they should be additive.

If you want a white headlamp, time to upgrade to the Seoul P4 U bins. Around 95 lumens at 350 mA(info from here, so 3 * 90 = 270 lumens at the LED).

:welcome:

Yeah, I was looking at those. They look nice particularly for that price. Thinking about making a whole new headlamp and reworking my circuit so I can use fewer batteries. Right now I'm using three CR123 so I can get close to 12 volts.

The reason I was asking about the Lumens is that a friend of mine thought you couldn't just add them. He said he thought it was a logarithmic scale. Something similar to how decibels don't just add together. He wasn't sure though.

I believe lumens are linear, but the human eye is logarithmic. Twice as many lumens will only look about 25% brighter.

Ah that makes sense. So as far as comparison goes I can add them. Thanks for your help.

In my first headlamp I used Cyan lights but I'm thinking about going with white this time. The logic was that as long as the light was on, since human eyes are more sensitive to green, that they could see more. Not really sure if it made a difference or not. I did look through one of threads on night vision but it seemed to focus on what color of light affected the ability of eyes to see in the dark the most.

What sort of lenses, if any, are recommended with the SSC P4 Z (u-bin)? Last time I used these http://www.l2optics.com/luxeon.aspx since that was what was used in the guide I followed. I went with the 15 degree ones and they seem to work well but again I don't really have any previous experience here; nothing to really compare them to.

I didn't really know what I was doing when I built the first. I still don't really know what I'm doing but I know a bit more and I'm learning which I suppose is a good thing.

El Conq said:

In case your curious I built it based on the following http://www.instructables.com/id/Ultimate-Night-Vision-Headlamp---500+-lumens-with-/

Click to expand...

Oh no, not that one again! Please go with white next time, since his comments about the cyan working better with your night vision are a total load of rubbish. I can explain in more detail, but am getting kind of bored of it. The white LEDs produce far more lumens than the coloured ones do, and it is only the lumens that matter. Meanwhile if you are after the brightest possible light and building from scratch then go with the Cree XR-E, since those are currently the brightest available. I'm using http://cutter.com.au/proddetail.php?prod=cut680 as my optics for these, which I find work very well, though there is now a huge selection of different ones available on that site if you use the search term "XR-E".

great project man. i would be buying another 5 units of luxeon stars in our place.

Sorry if that is a common post around here but I hard to start somewhere and I didn't know what I was doing so I just followed the guide. The light works well and I had no problems with it. I will compare it with the next one I build.

The Cree XR-E are nice but they are about $4 more a pop (for the Q5) which makes things a bit pricey. At least thats what they had on Deal extreme. Not sure yet which I will go with. Do most people around here purchase a pre-made driver circuit? Also is there much difference between lenses for these things besides fit and angle?

I hadn't considered reflectors before but I will certainly now.

Most Optics give you little to no spill but they are more efficient at transferring light then most reflector-window systems.

I think that most at least start with prebuilt circuit boards.

The Seoul P4 U bins are around the same performance as the Cree Q2-Q3 bins.

I think some Luxeon Optics would work with the Seoul LED.

I think I am going to go with two or three of the Cree XR-E Q5. I can get by on using fewer of them and still get greater light output which helps with the cost. I think I'll stick with optics, probably the ones recommended above.

Just need to decide on a driver and battery source. I'm considering using the same circuit I used last time (see first post). It seems to work well but I am open to any recommendations.

What battery voltage are you running?

If you are using a Cree LED, here are some relatively cheap optics(The Cree XR-E LED has a different emitting angle so it would require a different optic).

This driver can handle 3.7-18v.

I haven't decided on a battery layout or voltage. Something where I had the ability to change the battery source would be nice. I'm looking at dual duty with this thing between hiking/canoe trips and some night time bike riding. For hiking and canoe trips, the light doesn't need to be on for extended periods of time so I could go with some CR123's. For the bike ride I could go with AA or even C but AAs would probably be enough. I'm thinking 6v but thats a little low for two in series but a bit high for two in parallel.

Thanks for a link on the driver, I found a similar one on that site that allows for Hi/med/lo switching. I'll either do that or go with my own circuit again.

Just came across the 18650 batteries. I am considering something like this but will have to look into it more. I am seeing some varying measurements on the sizes of these things. Anybody have a link to some general info?

Li-ion batteries with numbers(usually):

First two numbers ate width in mm
Second two is length in mm
Last is shape(?)

So the 18650 battery would be 18mm wide, 65mm long and cylindrical. 14500 are AA size and 10440 are AAA sized.

Buy protected batteries, they are safer because they protect against overcharge(over 4.2v) and overdischarge(Under 2.7v). Both of which would degrade the battery faster and increase the chances of an explosion when you recharge the battery.

A 18650 battery is similar in voltage to 3 NiMh AA batteries in series(capacity depends on the batteries).

Also look at the Flashlight Electronics section if you have questions or want more info.