Lumen calculation

[yamcha]

Can some math whiz be kind enough to calculate some lumens for me? I have a 14.4volt battery and a 12volt, 20watt MR11 halogen lamp. I am hoping to get atleast 500 lumens out of this set up.

Thanks.

[JeffB502]

My understanding is that watts are a measurement of power consumed by the lamp, not how much light it generates. Much of the power consumed in a halogen lamp goes to creating heat. I would assume a higher quality lamp would produce more light and maybe less heat given the same power consumption (watts), so the output of your light would probably depend on the quality of your lamp, just like different 3 watt LEDs have different efficiency/light output at the same wattage.

Of course I could very well be wrong about this...I haven't looked into it too much, I just know when I bought a cheap 6v 20 watt MR11 lamp it seemed to put out less light than my 6v 15 watt MR11 Niterider lamp (running both off the standard 6v NiMH Trail Rat battery pack).

[yamcha]

Are you sure that it wasnt a 12v, 20w?

[JeffB502]

http://www.batteryspace.com/index.asp?PageAction=VIEWPROD&ProdID=2248

That's where I bought them (I got one 12 degree and one 24 degree). The receipt specified 6 volts, and both of the lamps had "6v20w" stamped on them (among other writing).

[JeffB502]

Check this out. They're automobile headlights but I think it illustrates how "watts" has some relationship to lumens but not a direct relationship.

http://www.sylvania.com/ConsumerProducts/AutomotiveLighting/Products/Halogen/StandardHalogenProducts/StandardHalogenProducts.htm

For example: From the website noted above, the following bulbs have the following outputs (in lumens) at 65 watts.
9004: 1200 +/- 15%
H13: 1500 +/- 15%
9007: 1350 +/- 15%
9005: 1700 +/- 15%

I guess maybe the shape of the bulb may make a difference in this case? Like I said I don't know much about this subject. Hopefully somebody that actually knows something will chime in :)

[bike_mike_pa]

This might help: http://nordicgroup.us/s78/wattslumens.html

After looking at that you might want to use an MR16, which will get you more light.

I've just rec'd a Sylvania High Efficicieny MR16 which is supposed to give the equiv. of 35 watts from a 20 watt bulb.

[bikingbrit]

Can some math whiz be kind enough to calculate some lumens for me? I have a 14.4volt battery and a 12volt, 20watt MR11 halogen lamp. I am hoping to get atleast 500 lumens out of this set up.

Thanks.

Quartz halogens are typically 24 lumens per watt, see:
http://en.wikipedia.org/wiki/Luminous_efficacy

So this gives you 20 X 24 = 480 lumens.

However you are running it at a higher voltage. Most "12 volt" lamps are actually specified at 12.8 volts (but the manufacturer's data should be consulted for an exact number.)

Light output of incandescent bulbs is proportional to the 3.4 exponent of voltage, see:
http://en.wikipedia.org/wiki/Incandescent_light_bulb

So ideally your 480 lumens would be boosted to 480 X (14.4/12.8)^3.4 = 716.4 lumens due to over-volting. In reality though you will have some voltage drop in the wires and connectors plus the battery voltage will decline a little as it discharges. 500 to 600 lumens is a reasonable estimate of actual output.

[acroy]

Quartz halogens are typically 24 lumens per watt, see:
http://en.wikipedia.org/wiki/Luminous_efficacy

So this gives you 20 X 24 = 480 lumens.

However you are running it at a higher voltage. Most "12 volt" lamps are actually specified at 12.8 volts (but the manufacturer's data should be consulted for an exact number.)

Light output of incandescent bulbs is proportional to the 3.4 exponent of voltage, see:
http://en.wikipedia.org/wiki/Incandescent_light_bulb

So ideally your 480 lumens would be boosted to 480 X (14.4/12.8)^3.4 = 716.4 lumens due to over-volting. In reality though you will have some voltage drop in the wires and connectors plus the battery voltage will decline a little as it discharges. 500 to 600 lumens is a reasonable estimate of actual output.

Great info Bikingbrit. this matches up very well with what Jetlights rate their halogen lights at.
Cheers

[H23Nutcase]

HID lumens per watt is around 80-100 lumesn per watt. I have a 35 watt HID headlight with 6000K bulb so I'm putting out about 3000 lumens. 4100K HID bulb suppose to have 3300 lumens, so that will be my next bulb if my current one burns out. Drivers think I'm a motorcycle....lol.



H23NC,

[edzo]

HID lumens per watt is around 80-100 lumesn per watt. I have a 35 watt HID headlight with 6000K bulb so I'm putting out about 3000 lumens. 4100K HID bulb suppose to have 3300 lumens, so that will be my next bulb if my current one burns out. Drivers think I'm a motorcycle....lol.



H23NC,

not really accurate in all HID systems. I had a 10watt HID (welsh/allyn) niterider and it was only 400 lumens

[H23Nutcase]

not really accurate in all HID systems. I had a 10watt HID (welsh/allyn) niterider and it was only 400 lumens

That's rather low. Probably your HID bulb is a different type of bulb rating. I'm using an automotive grade 6000k bulb powered with a 12V SLA battery rated @ 12AH. The rating can go as high as 9000K, which equals less lumens per watt.


H23NC,

[yamcha]

This might help: http://nordicgroup.us/s78/wattslumens.html

After looking at that you might want to use an MR16, which will get you more light.

I've just rec'd a Sylvania High Efficicieny MR16 which is supposed to give the equiv. of 35 watts from a 20 watt bulb.

Thanks, but the thing is my light housing doesn't take. a MR16 bulb, its too big. I also saw a 35w MR11 bulb at the hardware store. That would probably give me over 1000 lumens of light overvolted

[bikingbrit]

HID lumens per watt is around 80-100 lumesn per watt.
H23NC,

Pretty optimistic. The Wikipedia chart

http://en.wikipedia.org/wiki/Luminous_efficacy

lists "xenon arc" and "mercury zenon arc" lamps (which I believe are the same as HID) as being 30-50 and 50-55 lumens per watt respectively.

[H23Nutcase]

HID for automotive use is not xenon arc lamp. It's a metal halide type filled with xenon gas, see this:
http://en.wikipedia.org/wiki/Headlamp#HID_light_sources_.28Xenon_and_Bi-Xenon.29


Click on d2 Light source and that's the type of HID bulb I have: http://www.sylvaniaautocatalog.com/new_sylvania/Xenarchigh.asp


I don't know much about HID used for bicycles, probably is the ones you were talking about.


H23NC,


Pretty optimistic. The Wikipedia chart

http://en.wikipedia.org/wiki/Luminous_efficacy

lists "xenon arc" and "mercury zenon arc" lamps (which I believe are the same as HID) as being 30-50 and 50-55 lumens per watt respectively.

[Sir Bikesalot]

My understanding is that watts are a measurement of power consumed by the lamp, not how much light it generates. Much of the power consumed in a halogen lamp goes to creating heat. I would assume a higher quality lamp would produce more light and maybe less heat given the same power consumption (watts), so the output of your light would probably depend on the quality of your lamp, just like different 3 watt LEDs have different efficiency/light output at the same wattage.

Of course I could very well be wrong about this...I haven't looked into it too much, I just know when I bought a cheap 6v 20 watt MR11 lamp it seemed to put out less light than my 6v 15 watt MR11 Niterider lamp (running both off the standard 6v NiMH Trail Rat battery pack).

This is very true. Theoretically you should be able to get 700+ lumen from a 12V 20W MR11 running at 14.4V--BUT that's assuming a very high quality lamp. I've tried many commercially available MR11's (Philips, Ushio, a bunch from batteryspace, etc.) and I have to say they all suck. The absolute best 12V 20W MR11 lamp by a wide margin is actually the one that JetLites uses in their halogen systems. It's an 18 degree spot/flood that has a perfect beam pattern for both handlebars and helmet mount. Very uniform, very bright, with a nice halo for sidespill. It's $20, but really worth it. I've wasted far more than that trying out all the other ones (but I guess they'll make adequate backups).

http://jetlites.com/batteries.html
Look for #JA9602

[yamcha]

But the thing is this, I am overvolting so that means the bulbs won't last that long. So 20 bux is a lot.

[Sir Bikesalot]

But the thing is this, I am overvolting so that means the bulbs won't last that long. So 20 bux is a lot.

I believe it'll still last for hundreds of hours.

[Road Fan]

Quartz halogens are typically 24 lumens per watt, see:
http://en.wikipedia.org/wiki/Luminous_efficacy

So this gives you 20 X 24 = 480 lumens.

However you are running it at a higher voltage. Most "12 volt" lamps are actually specified at 12.8 volts (but the manufacturer's data should be consulted for an exact number.)

Light output of incandescent bulbs is proportional to the 3.4 exponent of voltage, see:
http://en.wikipedia.org/wiki/Incandescent_light_bulb

So ideally your 480 lumens would be boosted to 480 X (14.4/12.8)^3.4 = 716.4 lumens due to over-volting. In reality though you will have some voltage drop in the wires and connectors plus the battery voltage will decline a little as it discharges. 500 to 600 lumens is a reasonable estimate of actual output.


The voltage drops in the wires and contacts are really important. To see the bulb operating voltage you need to measure voltage at the bulb or as close as possible.

Halogen bulb brightness (lumen ouput) is a sensitive function of voltage, as is life. Depending on your wire choice there could be 2 volts of loss through the wiring, and partly due to internal battery resistance. The 14.4 volt batter could be spec'd based on it's unloaded voltage when new and fully charged, and it could be entirely reasonable that it delivers 12.5 V at the lamp, especially at partial charge or after a good number of charge/discharge cycles.

Road Fan, former automotive lighting power electronics engineer

[bikingbrit]

The voltage drops in the wires and contacts are really important. To see the bulb operating voltage you need to measure voltage at the bulb or as close as possible.

Halogen bulb brightness (lumen ouput) is a sensitive function of voltage, as is life. Depending on your wire choice there could be 2 volts of loss through the wiring, and partly due to internal battery resistance. The 14.4 volt batter could be spec'd based on it's unloaded voltage when new and fully charged, and it could be entirely reasonable that it delivers 12.5 V at the lamp, especially at partial charge or after a good number of charge/discharge cycles.

Road Fan, former automotive lighting power electronics engineer

Too true! A "12 volt" automobile will typically have 14.0 volts (+/- 0.5 volt) at the voltage regulator terminal when the engine is running. I expect the reason "12 volt" bulbs are usually specified at 12.8 volts is due to the typical wiring/connector/socket/switch voltage drops.

Those who think they are seriously "overvolting" a bulb by using a 14.4 volt battery are probably deluding themselves.

[ovrrdrive]

One thing a bunch of you are overlooking is that a 14.4V battery is no more a 14.4V battery than a 12V is 12V. They are actually putting close to 16V at full charge. cyccommute has stated several times that an overvolted MR16 is laying over 1000 lumens to the road. I'm not sure where eh learned his math but he seems pretty darned knowledgeable in this stuff, and after seeing my overvolted MR16 in person it isn't hard for me to believe...

Quartz halogens are typically 24 lumens per watt, see:
http://en.wikipedia.org/wiki/Luminous_efficacy
So this gives you 20 X 24 = 480 lumens.
However you are running it at a higher voltage. Most "12 volt" lamps are actually specified at 12.8 volts (but the manufacturer's data should be consulted for an exact number.)
Light output of incandescent bulbs is proportional to the 3.4 exponent of voltage, see:
http://en.wikipedia.org/wiki/Incandescent_light_bulb
So ideally your 480 lumens would be boosted to 480 X (14.4/12.8)^3.4 = 716.4 lumens due to over-volting. In reality though you will have some voltage drop in the wires and connectors plus the battery voltage will decline a little as it discharges. 500 to 600 lumens is a reasonable estimate of actual output.

So, using your formula with a closer to the truth 16V instead of 14.4V yields this:

480 X (16/12.8)^3.4 = 1025 lumens...

Which is right about what it looks like in person...

[znomit]

You need to measure the battery voltage with the lamp turned on for a true reading. Internal battery resistance drops the voltage at the battery terminals once you turn the light on. Hence your 12.8v at full charge most likely is with the batteries off. Full charge also might last until you get your bike out the driveway.
I run NiMH AAs and I see 1.3v for a short time and then 1.1-1.2v for several hours.
This isn't going to help calculate lumens though.

I guess to answer the OP's question, no amount of math will tell you how many lumens your unknown brand bulb running off an unknown battery at an undetermined voltage is outputing.
BUT...if its not bright enough, get a higher wattage (or narrower beam)bulb. If it doesn't burn long enough, get a bigger battery.

[Fibber]

I think 24 l/w may be a bit optimistic. You might find some 'high state of tune' units that give that and more, but I question whether it could be deemed 'typical'. If you check out some of the writings of Daniel Stern (an automotive lighting guru), he lists power draw and output for a large number of the 12 bulbs commonly available. The best high beams put out 1700 l @ 65w, or 26 l/w, but that is atypical. Common low beams, operating at 55w are down under 20 l/w. Part of the problem is US DOT regs that limit output, and thus what you can find sold in America. In Europe, for instance, you can get stuff that easily exceeds by 25%.

LED is coming on strong. I bought some flashlights recently with 3 watt (Philips Luxeon III) emitters that put out around 75 lumens, or around 25 l/w. Some of the high end stuff available / affordable is good for around 50 l/w. Compare that to most halogen flashlights, with around 15-18 l/w typical.

HID numbers are all over the place, so it is hard to know the truth. Because the emission area is large and not pinpoint, it depends as much on the optics system as anything how useful the light will be.

Comments about actual voltage available are valid. A wet cell car battery puts out around 12.8v with no load. Put a draw on it, and it measures lower. Your regulated alternator put out 14.5v, but note how quickly even that dims when you throw on a load. I doubt a rechargeable battery would hold the advertised voltage for very long, so I question whether you are getting the 'overvoltage' you are expecting.

[znomit]

Good article here if you can read german, ok article if you can't!
http://www.mtb-news.de/forum/showthread.php?t=298107&page=6

If you have a look around on the interweb you will be able to find some articles talking about lumens from halogens. Find the one that give your lights the biggest numbers and quote that. OMG Lumens!

[ken cummings]

I looked at that Wikipedia article about luminous efficiency. Low Pressure sodium lights run to 200 lumens per watt. Holy Photons Batman! Well, I've known about LPS for decades, pity they are not too vibration resistant. The day a tough LPS light hits the market I'll replace the Cessna headlight on my bike and start putting 10,000 to 15,000 lumens down the road.

[yamcha]

You have the name of a porn star!