True Usable light power ?

[colinicky]

Following on from my previous thread about Lux & Lumens I had an interesting exchange of emails with 2 torch manufacturers who both said that Lumens are no good to us as divers because that is the amount of light put out in 360 degrees & that a "Lux" reading is a truer reading of the light as this reading is taken after the light has left the torch head so also takes account of good/bad reflector design . One said that the 10w Welch Allen (sp) bulb is rated at 500 lumens & that the greenforce has 7500 Lux but the Diverite using the same bulb has 10000 Lux due to a much better reflector .
Any thought ? maybe manufacturers should list both readings ?

[johnkendall]

Originally Posted by colinicky

Following on from my previous thread about Lux & Lumens I had an interesting exchange of emails with 2 torch manufacturers who both said that Lumens are no good to us as divers because that is the amount of light put out in 360 degrees & that a "Lux" reading is a truer reading of the light as this reading is taken after the light has left the torch head so also takes account of good/bad reflector design . One said that the 10w Welch Allen (sp) bulb is rated at 500 lumens & that the greenforce has 7500 Lux but the Diverite using the same bulb has 10000 Lux due to a much better reflector .
Any thought ? maybe manufacturers should list both readings ?

The problem with LUX as a measure is that it depends on a number of factors (Distance from object, medium through which the light is travelling etc)

If they tell you under which circumstances the tests were done, then it becomes more meaningful. Lumens on the other hand are an absolute measure of the bulb. If you have a 100% efficient reflector (which doesn't really exist in the world of dive lights) then 500 lumens, hitting an area of 1m^2 would be 500 LUX, and if it was hitting an area 10cmx10cm it would be 50000 LUX, so you can see how beam angle effects LUX a lot, whereas they are still the same LUMENS.

HTH

John

[colinicky]

AIUI Lux is measured as standard 1m from the light source in air ?

[divingniknaks]

I understand where you're coming from.

The reason some manufacturers quote in different units is entirely so that you can't make a direct comparison.

One particular popular manufacturer doesn't quote figures of any kind (that I can find anyway) and that really does make me wonder. But they still still sell seemingly well.

Like I said the other day, you know deep inside what you really want to do, so stop putting it off and call me

.

[colinicky]

Originally Posted by divingniknaks

One particular popular manufacturer doesn't quote figures of any kind

One of the 2 mentioned above ? Still waiting an answer from them !

So were are the Lux figures for Salvo then ?

[divingniknaks]

Originally Posted by colinicky

AIUI Lux is measured as standard 1m from the light source in air ?

Lux takes into account the area over which you are spreading the light.

"The difference between the lux and the lumen is that the lux takes into account the area over which the luminous flux is spread. 1000 lumens, concentrated into an area of one square metre, lights up that square metre with an illuminance of 1000 lux. The same 1000 lumens, spread out over ten square metres, produces a dimmer illuminance of only 100 lux."

HTH

[johnkendall]

Also, to go past the numbers, what is it that you are actually trying to achieve? You can have a light that has a low LUX listing, yet high LUMENs because it has a very wide beam angle, conversly If you had a very narrow beam angle the LUX reading could be massive from a low LUMEN.

Better is to try and work out what is important for you with a light, i.e general illumination, good signalling ability, large light output over a large area etc etc, all of these are useful for different things, so for Video you need a wide beam angle with a lot of light behind it, for signalling then you don't need that much light but it needs to be very narrow.

HTH

John

[divingniknaks]

Originally Posted by colinicky

One of the 2 mentioned above ? Still waiting an answer from them !

So were are the Lux figures for Salvo then ?

As John has said Lumens is actually a better measure for a direct comparison, which is why Salvo quote Lumens.

Actually not one of the ones above.

.

[divingniknaks]

Originally Posted by johnkendall

Also, to go past the numbers, what is it that you are actually trying to achieve?

He's trying to justify buying a Salvo


(I think)

[colinicky]

Understand what your saying .the way I was led to believe was it was the amount of light hitting a 1 metre square at 1 metre distance .Haven't done the maths to see whjat beam angle you could get upto before you spilled outside the 1m square though .