Confused about Lux

[BOBBYBOB]

First post, I am excited to be here. I have been into flashlights for almost
50, yes 50 years!! I am sure I will learn a lot here. I have a Fenix P1D,
an older one that puts out 130 Lumens. What is the difference between
Lux and Lumens? Thank you for the help

 

[Marduke]

First post, I am excited to be here. I have been into flashlights for almost
50, yes 50 years!! I am sure I will learn a lot here. I have a Fenix P1D,
an older one that puts out 130 Lumens. What is the difference between
Lux and Lumens? Thank you for the help

Lumens is total output, lux is a measure of how well the light throws (projects a given distance).

:welcome:

 

[Steve L]

Lumens are the total amount of light produced. Lux is measurement of spot intensity taken a 1 meter. EX: Two different lights each with a Q5 running at 1 amp will both produce ~250 lumens. The one with the wider and deeper reflector will be able to focus the beam tighter and produce a higher lux reading(a smaller brighter hot-spot that will produce longer throw).

 

[H20doctor]

So then how do you convert Lumens to watts..? If a cree driven at 1000Ma is 220 Lumens... Then How many actualy watts of power is that..? The Cree xre Led's

 

[Gunner12]

Converting watt to lumen will depend on the efficiency of the light source. The Cree XR-E driven at 1000 mA is consuming around 3.7 watt of power but only produces around 1 watt of light. The Luxeon III driven at 3.7 watt only produces around 0.35-0.4 watt of light.

BOBBYBOB:

The Welcome Mat would explain many of the things you'll see around here. This page is also good for explaining the difference between lux and lumen.

I'm guessing that you have already read about the current gen LEDs.

:welcome:

 

[H20doctor]

I read both of those.. But it doesnt Help me cause I am a newbie.. 4 cree xre at 1000Ma Luxdrive driver is 12 watts.. But how much light out put is that..? 35 watts..? 50 watts..?

 

[Lightguy27]

:welcome: Lux is a measurement taken usually at one meter to determine how well a light projects or throws it's light output over distance. Lumens is calculated by an Integrating Sphere and measures the total useable light output. Lumens are the best unit for measuring light output because of the fact that they measure total availible light.

-Evan

 

[H20doctor]

But there should be a standard config. if a cree puts out 200 lumens at 1000Ma what is that equivelant to in wattage..? 4 cree +1000ma= ? watts which is equiv. To a 35 watt bulb.?.a 20 watt HID.? there should be something ? The same with a Luxeon emmiter or other Led's ?

 

[Marduke]

I read both of those.. But it doesnt Help me cause I am a newbie.. 4 cree xre at 1000Ma Luxdrive driver is 12 watts.. But how much light out put is that..? 35 watts..? 50 watts..?

Lumens doesn't equal watts, it's like converting gas mileage and horse power. There might be a VERY loose relation there, but it depends a lot on the car and engine being used. It's also like comparing technology of the 1920's with today. Not a very accurate comparison.

 

[Gunner12]

4 Cree XR-E Q5 at 1000 mA would be around 3.5-3.7v. I'll presume 3.7v.

So 3.7v * 1 amp * 4 LEDs = 14.8 watt. According to this data, the Q5 is around 65 lumen per watt when driven at 1000 mA. So 14.8 watt * 65 lumen/watt = 962 lumen.

If the LED was 30 lumen per watt, then 14.8 watt * 30 lumen/watt =444 lumen.

The amount of lumen will depend on the efficiency of the emitting source. The current gen LEDs are on average a bit above double the efficiency of the last gen LEDs, so for the same wattage, the current gen LEDs will output twice the lumen.

 

[enLIGHTenment]

Lumens are a measure of luminous flux, the total light output of a light source adjusted for the wavelength sensitivity of the human eye. In the flashlight context, this would be the total amount of light which escapes trough the optical window (front 'lens').

Lux are a measure of illuminance, or how much light is falling on a surface such as a wall or light meter. In the flashlight context, lux readings are usually taken with a light meter placed 1 metre from the flashlight. Lux values give a rough indication of the effective illumination range of a light.

Lumens and lux cannot be converted.

Watts are a measure of power. In the flashlight context, wattage values usually mean the rated power of the emitter (bulb or LED) or the amount of electric power provided to the emitter. For example, a 3 watt LED flashlight is assumed to provide three watts of power to the LED.

Input power in watts can be approximately converted to light output in lumens if the emitter efficiency is known. Efficiency is rated in lumens per watt (lm/w). It naturally follows that a 3W LED with an efficiency of 100lm/w will produce 300lm of light. The flashlight will not emit 300lm, however, due to light losses in the optics. %20-%30 losses are to be expected between the emitter and optical window.

Light power can be measured in radiometric terms using watts. This system of measurement, however, is generally used only for lasers and industrial, scientific and medial equipment. Radiometric power measurements are never used for flashlights.

 

[H20doctor]

thank you gunner12 for the breakdown... you have been very helpfull. So at 962 Lumens which is almost 1000 lumens.. Then thats a bright mother of a light... I have used the Fraen lens on my light rather than the 18mm alumn lens from deal extreem..

 

[Gunner12]

962 at the emitter would probably mean 700-800 out the front after you include losses from the optics/reflector. Normally efficiency of a reflector window combo is about 70-80% efficient, so you will loose 30-20% of the light in the reflector and the window(some times called the lens).

You can get even more output when the higher bin LEDs come out. 1400 lumen with 14 watt input might be possible with a year or two.

enLIGHTenment also explained it pretty well.