LED flash light, lumens vs candle power. Vash?
 

Plumber comes by my job late and its dark. I usually have my Ultra Stinger In my Land Cruiser. Today it's completely discharged. So I off I go to the Target to buy a new flashlight. I was thinking about a LED Mag Light. I come across this off brand, LED Dorcy, that claims to have 160 lumens. For $35 I purchased it because I really needed a light with my dumb a$$ plumber waiting there. To my surprise, this cheap little light is really bright. I charged up my Ultra Stringer and was comparing the two in my back yard just before I am typing this( I have a mile of pitch black canyon to test it). At 75' the Dorcy is brighter then my Streamlight. I am really surprise there, because it is a tool and not just some kid flashlight. anything beyone that, the Streamlight can focus and tighten its beam so it is brighter in the longer distance.

This Dorcy runs 6 AAA batteries.

Just how bright is 160 lumens? Why don't LEDs stick with candle power?

You ought to know this stuff! ;)

A candela (or candlepower) is a measure of light SOURCE output. A lumen is a measure of light intensity at an object or point.

A given light source might make a lot of candleas but depending on how diffuse it is (scatter) or what's in between the source and destination (like a dirty lens or whatever) the lumens may be significantly lower.

LEDs tend to be directional so I'd expect little loss between the source (candlepower) and the destination object (lumens). They do tend to have very poor off-center illumination though due to how naturally directional they are - they require reflectors/diffusers to scatter the light.

From a practical standpoint, what you're really concerned about is lumens, almost never candlepower.

I have it that Stingers don't 'like' to be completely discharged, that it is better for the battery to quit using when you first notice it going dim.
Thank for the lumens/candlepower info Jeff.
Jim

Looked at some lights yesterday and am just not excited about any flashlight using AAA batteries. Too damm expensive and usually do not last long. Would much prefer AA models and do not mind the light being a bit thicker to accomodate this.

great explanation!

i cant believe the plumber didnt have a flashlight.

He left all his tool over at another job. He uses those tool combo flashlight thing. I am really started to like LEDs after this.

Thank Jeff, I didn't know that.

I have the Coleman Max LED light.. 140 lumens, 3 AAA batteries... $26. bought 2 more for house and truck.

there are LEDs being used in auto headlights now...

for bright LEDs, you want to pay attention to what the bike light people are doing - Nite-Rider is ahead of the pack (but not cheap)

if you wait a while, the price per lumen will be lower...

and, BTW, there is some R&D on a much more efficient light source than even the LEDs... I forget where I saw that tho.

hope you are all able to manage your steradians during the holidaze...

I have gone to rechargeable batteries for pretty much everything myself.

LED's are pretty bad ass.

Not for headlights but for DRLs and marker lights.

White LEDs are produced using a blue LED and red and green phosphor in the package where the oputput combines into what your eye thinks is white light when you look at it. The output has a distinct spike in the blue spectrum and smaller blobs in the green and red as opposed to the continuous spectrum of sunlight or incandescent. If you look at an object this light reflects off of it may have some strange colors, not suitable for driving.

Sorry to go off topic but...

Standard cars will have LED headlights in the next 18 months, according to headlight maker Hella.

Lexus LS600h with LED low beams:
http://images.thecarconnection.com/m...00219754_m.jpg

Audi R8 will be available with LED high/low beam in 2010

New LED's are just off the chart when it comes to light density.

Google for SST-90.

It maxes out at around 3000 lumen (!), draws near 9A of current and needs sizeable heatsink to keep it cool.

http://forums.pelicanparts.com/uploa...1260450233.jpg

Ooops. I stand corrected. I was using information I got at from an LED driver seminar from a couple years ago.

yup - 2 years is ancient history with these things

I'd like to see it move even faster.


Back OT:

you have a light source... you can measure all the radiation it gives off in every direction or in just a "beam"

then you can weight the visible radiation by the sensitivity of the human eye to wavelength

then you can measure the flux of rad. thru say 1 m2 "in the stream"

and then... you can measure the radiation falling on a surface somewhere...

also do it in SI or Brit. units

complicated enuff yet?