How do you do the above? How come some lights are quoted in watts and some in lumens?
Bike Forum
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comparing light outputs Watts vs Lumens
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Posted 2 years ago #
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watts is the power they use
lumens is the light they emitPosted 2 years ago # -
any idea what wattage an exposure joystick it? its 240 lumens
Posted 2 years ago # -
You can't.
Watts was used previous when pretty much all lights were halogens so you could just compare the power used by the bulb(s) - eg you knew that a 40W light was more powerful than a 20W one.
With LEDs and HIDs, the comparison no longer works because 10W of LED is brighter than 10W of halogen so lumens are used which is an actual measure of the light produced but the accuracy of these is very variable...
Posted 2 years ago # -
as a VERY rough guide, IIRC 200 lumens is roughly what a 10W halogen produces
Posted 2 years ago # -
Watts and lumens can't be directly compared any more.
A 10w halogen produces less light than a 10w LED.
Watts is nothing to do with the amount of light, only the amount of current the battery draws from the bulb. When everything was Halogen, a 10w bulb could be compared to a 20w one, but now there are 3 different types of bulb (Halogen, LED, HID) all drawing different current (Wattage) for the same light output, all that does is confuse things.
EDIT
And then of course there's the 'colour' of the beam. Clubber is about right with his estimation, but a 240 lumen Joystick looks about double the power of my old 10w Halogen, at least....Posted 2 years ago # -
Watts is what power a light uses.
Lumens is the amount of light it produces. Thus you cannot compare them both as it will depend on the type of bulb you have.
For halogens the wattage will be higher for the same amount of light/lumens as an LED will produce.
So if they quote lumens it's a better indicator of what light is actually produced.
Posted 2 years ago # -
Shall we try Lux ?.
L.
Posted 2 years ago # -
watts was meaningless even for halogens, as some of them over-volted, or used more efficient halogen bulbs, meaning two different halogens with 10w bulbs in could differ in actual light output by 40-50%.
Lumens are also slightly meaningless, in that most manufacturers don't actually measure it and just make up lies about it based on the theoretical maximum output of the LED that they are using, ignoring things like optics/reflectors that make things less efficient or ignoring how much current they are putting into it.
Joe
Posted 2 years ago # -
see my old post on some measurements of my DX light - 1500Cd/m2 and 5k lux at 1m.
http://www.singletrackworld.com/forum/topic/dx-light-some-measurements
Posted 2 years ago # -
Posted 2 years ago #
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Watts is just power consumed so no guide to the output e.g. a 1000 Watt electric bar fire is very dim.
Candela measures simple luminous intensity so relates to the rate of photons emitted.
4π lumens is the total luminous flux of a light source of one candela (takes the light cone into account I think).
One lux is equal to one lumen per square metre i.e. the actual lighting effect on a surface area.Posted 2 years ago # -
Watts is still a useful measure as long as you understand what it means. It is usually used to define the input power of the light at it's nominal voltage so it will help you work out how long your batteries will last (a 10W halogen will use as much energy as 10W of LED lights).
Obviously some of that input energy is wasted as heat but that which is converted into light (across the whole EM spectrum) is also measured in Watts and known as radiant power.
Lumens is also a measure of the energy converted to light but this time it is weighted to reflect how the human eye is sensitive to different wavelengths of light. It gives us an indication of the output that is 'useful' to us so a halogen bulb and UV bulb might have the same input and radiant powers but the UV bulb would have virtually zero lumens as we can't see the light. It also means that the colour of light given out will affect the lumen rating slightly as a light that gives more green/yellow light will be easier for us to use than one that has a lot of blue light.
Lux is simply the amount of lumens that pass through a given metre square in the beam. Obviously this will vary depending on where in the beam the measurement is taken and the distance from the bulb (as the light is diverging). Therefore it is only really useful if it is given with the measurement position in relation to the beam. It's used because it's easier to physically measure the amount of light over a small area than it is to try and measure all the light that a bulb gives out.
Posted 2 years ago # -
Lux is simply the amount of lumens that pass through a given metre square in the beam. Obviously this will vary depending on where in the beam the measurement is taken and the distance from the bulb (as the light is diverging). Therefore it is only really useful if it is given with the measurement position in relation to the beam. It's used because it's easier to physically measure the amount of light over a small area than it is to try and measure all the light that a bulb gives out.
This kind of describes why I think using Lux might be useful for us.
If the lighting community can agree a position and distance, then wouldn't all Lux measurements then be useful ?.
Furthermore, this can help people understand whether a light is producing what they are looking for in terms of light intensity, as a function of beam pattern.Measuring all the light a source produces isn't necessarily useful to people who are tyring to understand whether a particualr light is suitable for their needs, by basing a judgement on a quoted figure.
Hence group tests and when people remark that a light is "too floody" or "too spot beam like".Consider, an LED will produce the same Lumens with, or without a collamator. But only an LED used with the collamator would be useful for night riding, imo.
All this though with the caveat that we don't end up with lights that produce just very tight spot beams, in order to win a Lux-reading-war, and perhaps this is the limitation of Lux.
L.
Posted 2 years ago # -
As mentioned above you must treat quoted lumen figures with caution. The Nightrider 600 that TBC lent me for the puffer is "only" 600 lumen - but they are shire horses not pit ponies and its brighter than any other light I have seen - including my homemade MCE led which is a theoretical 900 lumen and its brighter than a 900 lumen dx.
YOu need to know what lamp unit / led is being used to give a real comparison.
Posted 2 years ago # -
TJ.
This is why I think Lux could help. I came to appreicate a long time ago, that just looking at lumens doesn't always give a great riding light.
I experienced this best with XR-E LEDs.
With the right "optic" I can really make them punch above their weight and give a very nice result for ST.
With Lux, I'm getting an idea of the intensity being produced from a light, ie, a light with a good LED and optic combo would yeild a higher Lux reading over a certain area, at a certain distance.
I think that this would be useful to MTB'ers as we're looking for most of our light to be put down in a certain area, at a certain distance.
I can well believe that a 600 Lumen light can appear to be brighter than others quoting higher lumen outputs. I have a triple XR-E which I preferred to my 6 x XP-E light. Yet on paper, the triple was supposed to give around 675 lumens and the 6 x XP-E around 1200 lumens.
Had I been using Lux, then I think the numbers would have been more in line with what I actually saw when I switched these lights on.
Its just a thought.
L.
Posted 2 years ago #
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