I was just looking at this head torch, which claims to output 6000 lumens.

https://www.amazon.co.uk/gp/product/B078NCZ6KC?

That exceeds the output from a 5 foot fluorescent tube, which seems
unlikely. I know LEDs are more efficient, but not that much more, and
the tube is consuming 60w.

What's going on? Lies?

"GB" wrote in message
news
I was just looking at this head torch, which claims to output 6000 lumens.

https://www.amazon.co.uk/gp/product/B078NCZ6KC?

That exceeds the output from a 5 foot fluorescent tube, which seems
unlikely. I know LEDs are more efficient, but not that much more, and the
tube is consuming 60w.

What's going on? Lies?

Maybe because it has a reflector so the light is all directed one way,
whereas a fluorescent tube is all round (apart from where the fitting is).

On 02/07/2018 11:08, NY wrote:
"GB" wrote in message
news
I was just looking at this head torch, which claims to output 6000
lumens.

https://www.amazon.co.uk/gp/product/B078NCZ6KC?

That exceeds the output from a 5 foot fluorescent tube, which seems
unlikely. I know LEDs are more efficient, but not that much more, and
the tube is consuming 60w.

What's going on? Lies?

Maybe because it has a reflector so the light is all directed one way,
whereas a fluorescent tube is all round (apart from where the fitting is).


Lumens are defined as the light per unit of solid angle. So, focusing
the same amount of light into a tight beam does indeed increase the
lumens. Still...

On 02/07/2018 12:59, GB wrote:
On 02/07/2018 11:08, NY wrote:
"GB" wrote in message
news
I was just looking at this head torch, which claims to output 6000
lumens.

https://www.amazon.co.uk/gp/product/B078NCZ6KC?

That exceeds the output from a 5 foot fluorescent tube, which seems
unlikely. I know LEDs are more efficient, but not that much more, and
the tube is consuming 60w.

What's going on? Lies?

Maybe because it has a reflector so the light is all directed one way,
whereas a fluorescent tube is all round (apart from where the fitting
is).


Lumens are defined as the light per unit of solid angle. So, focusing
the same amount of light into a tight beam does indeed increase the
lumens. Still...

I may be mistaken but my memory is that lumens are a measure of the
total output (flux). The measure of the "brightness" of a focused beam
is it's luminous intensity, for which the unit is candela (lumens per
steradian). So the ad is unsurprisingly ********.

It's a bit counter-intuitive because a candela comes from the light from
a candle - but the _intensity_ of the candle, not its _total_ flux.



--
Robin
reply-to address is (intended to be) valid

On 02/07/2018 14:16, Robin wrote:
On 02/07/2018 12:59, GB wrote:
On 02/07/2018 11:08, NY wrote:
"GB" wrote in message
news I was just looking at this head torch, which claims to output 6000
lumens.

https://www.amazon.co.uk/gp/product/B078NCZ6KC?

That exceeds the output from a 5 foot fluorescent tube, which seems
unlikely. I know LEDs are more efficient, but not that much more,
and the tube is consuming 60w.

What's going on? Lies?

Maybe because it has a reflector so the light is all directed one
way, whereas a fluorescent tube is all round (apart from where the
fitting is).


Lumens are defined as the light per unit of solid angle. So, focusing
the same amount of light into a tight beam does indeed increase the
lumens. Still...

I may be mistaken but my memory is that lumens are a measure of the
total output (flux).Â* The measure of the "brightness" of a focused beam
is it's luminous intensity, for which the unit is candela (lumens per
steradian).Â* So the ad is unsurprisingly ********.

I thought much the same as you, but checked it before I wrote the above.

Lumen = the SI unit of luminous flux, equal to the amount of light
emitted per second in a unit solid angle of one steradian from a uniform
source of one candela.

Of course, you are right in practice, because you very rarely need to
illuminate a tiny spot with intense light whilst leaving everything else
in darkness.

On 02/07/2018 14:30, GB wrote:
On 02/07/2018 14:16, Robin wrote:
On 02/07/2018 12:59, GB wrote:
On 02/07/2018 11:08, NY wrote:
"GB" wrote in message
news I was just looking at this head torch, which claims to output 6000
lumens.

https://www.amazon.co.uk/gp/product/B078NCZ6KC?

That exceeds the output from a 5 foot fluorescent tube, which seems
unlikely. I know LEDs are more efficient, but not that much more,
and the tube is consuming 60w.

What's going on? Lies?

Maybe because it has a reflector so the light is all directed one
way, whereas a fluorescent tube is all round (apart from where the
fitting is).


Lumens are defined as the light per unit of solid angle. So, focusing
the same amount of light into a tight beam does indeed increase the
lumens. Still...

I may be mistaken but my memory is that lumens are a measure of the
total output (flux).Â* The measure of the "brightness" of a focused
beam is it's luminous intensity, for which the unit is candela (lumens
per steradian).Â* So the ad is unsurprisingly ********.

I thought much the same as you, but checked itÂ* before I wrote the above.

Lumen = the SI unit of luminous flux, equal to the amount of light
emitted per second in a unit solid angle of one steradian from a uniform
source of one candela.

Yes, that's why I said it's counter-intuitive. Let's try starting with
the definition you quote:

"Lumen = the amount of light emitted per second in a unit solid angle of
one steradian from a uniform source of one candela"

4 Pi lumens = the amount of light emitted per second from a uniform
source of one candela

8 Pi lumens = the amount of light emitted per second from a uniform
source of 2 candela

etc.

Now suppose all the light from the sources is focused by a mirror so it
is emitted over a hemisphere. Has the total amount of light emitted
increased because it's now all emitted into 2 Pi sr? Or is it that the
intensity has increased?

But it may be clearer at

https://en.wikipedia.org/wiki/Luminous_intensity
























Of course, you are right in practice, because you very rarely need to
illuminate a tiny spot with intense light whilst leaving everything else
in darkness.



--
Robin
reply-to address is (intended to be) valid

GB wrote:

Lumens are defined as the light per unit of solid angle. So, focusing
the same amount of light into a tight beam does indeed increase the
lumens. Still...

I thought Lumens was Lumens (probably should be lowercase) and if you
wanted to include the angle they were spread over, it was something like
lumens per steradian?

On 03/07/2018 00:19, Andy Burns wrote:
GB wrote:

Lumens are defined as the light per unit of solid angle. So, focusing
the same amount of light into a tight beam does indeed increase the
lumens. Still...

I thought Lumens was Lumens (probably should be lowercase) and if you
wanted to include the angle they were spread over, it was something like
lumens per steradian?

I think that's the definition of a candela.

--
Max Demian

On 02/07/2018 10:58, GB wrote:
I was just looking at this head torch, which claims to output 6000 lumens.

https://www.amazon.co.uk/gp/product/B078NCZ6KC?

That exceeds the output from a 5 foot fluorescent tube, which seems
unlikely. I know LEDs are more efficient, but not that much more, and
the tube is consuming 60w.

What's going on? Lies?

I think lumens is the total amount of light coming from something, so it
must be lies.

Bill

Bill Wright wrote:

On 02/07/2018 10:58, GB wrote:

I was just looking at this head torch, which claims to output 6000
lumens.

https://www.amazon.co.uk/gp/product/B078NCZ6KC?

What's going on? Lies?

I think lumens is the total amount of light coming from something, so it
must be lies.

I think 6000 lumens is lies. I have a Fenix LED torch, powered by a
single 4.2V 4800mAh 26650 cell, Cree spec sheets say the LED used has a
peak power consumption of 18W, which gives 1600 lumens, it's about as
bright as a halogen headlamp.

For that headtorch, Cree's spec say each LED is 1040 lumens, so 3120
total and I'd expect that to melt your forehead in pretty short order ...

On 03/07/2018 00:32, Andy Burns wrote:
Bill Wright wrote:

On 02/07/2018 10:58, GB wrote:

I was just looking at this head torch, which claims to output 6000
lumens.

https://www.amazon.co.uk/gp/product/B078NCZ6KC?

What's going on? Lies?

I think lumens is the total amount of lighyt coming from something, so
it must be lies.

I think 6000 lumens is lies. I have a Fenix LED torch, powered by a
single 4.2V 4800mAh 26650 cell, Cree spec sheets say the LED used has a
peak power consumption of 18W, which gives 1600 lumens, it's about as
bright as a halogen headlamp.

For that headtorch, Cree's spec say each LED is 1040 lumens, so 3120
total and I'd expect that to melt your forehead in pretty short order ...

The 1040 lumens figure is probably specified at 25C which suggests it's
only achievable when attached to a very large heat-sink. I doubt if the
typical forehead is a suitable heat-sink.

I would also be a bit worried about supplying that much power from 2 x
18650 batteries strapped to the back of your head.

I have a couple of (Chinese) "Cree" mini torches that take the shorter
lithium 14500 3.7V 1600mAh[1] battery. They provide a very bright light
for all of 3 or 4 minutes before the all metal casing gets rather hot
and the light output falls of dramatically. I'm not sure if its the LED
trying to ditch heat or the battery warming up to trying to supply the
power. I also have the much larger models of these torches with the
18650 1800mAh[1] 3.7V battery that don't seem to have this problem
possibly because the all metal case is substantially larger providing a
better heat-sink.

[1] Chinese specification for many of these no-name batteries, which is
often BS. Ebay lists 14500 anywhere between 750mAh and 2600mAH - I
suspect that the former figure is somewhat closer to the truth.

--
mailto : news {at} admac {dot} myzen {dot} co {dot} uk

On Mon, 2 Jul 2018 10:58:17 +0100, GB
wrote:

I was just looking at this head torch, which claims to output 6000 lumens.

https://www.amazon.co.uk/gp/product/B078NCZ6KC?

That exceeds the output from a 5 foot fluorescent tube, which seems
unlikely. I know LEDs are more efficient, but not that much more, and
the tube is consuming 60w.

What's going on? Lies?

The 'Tech Details' seem very confused, going from 5 to 6k lumens, it
running on 2 x AAA or 2 x 18650 batteries, a sound level of 5dB and
that batteries aren't required or included?

I'll stick with my little Petzl headlight. ;-)

Cheers, T i m

On 02/07/2018 10:58, GB wrote:
I was just looking at this head torch, which claims to output 6000 lumens.

https://www.amazon.co.uk/gp/product/B078NCZ6KC?

That exceeds the output from a 5 foot fluorescent tube, which seems
unlikely. I know LEDs are more efficient, but not that much more, and
the tube is consuming 60w.

What's going on? Lies?

The same lies as the 12v amplifier I bought last year. Claims 500 watts,
utter piffle i'd rate it at 5 Watts which was perfect for my application.

Mike

On Mon, 2 Jul 2018 13:51:07 +0100, Muddymike
wrote:

On 02/07/2018 10:58, GB wrote:
I was just looking at this head torch, which claims to output 6000 lumens.

https://www.amazon.co.uk/gp/product/B078NCZ6KC?

That exceeds the output from a 5 foot fluorescent tube, which seems
unlikely. I know LEDs are more efficient, but not that much more, and
the tube is consuming 60w.

What's going on? Lies?

The same lies as the 12v amplifier I bought last year. Claims 500 watts,
utter piffle i'd rate it at 5 Watts which was perfect for my application.

I love it, 'Peak music power' and both channels added together. ;-)

Cheers, T i m

On Mon, 02 Jul 2018 15:15:56 +0100, T i m wrote:

On Mon, 2 Jul 2018 13:51:07 +0100, Muddymike
wrote:

On 02/07/2018 10:58, GB wrote:
I was just looking at this head torch, which claims to output 6000
lumens.

https://www.amazon.co.uk/gp/product/B078NCZ6KC?

That exceeds the output from a 5 foot fluorescent tube, which seems
unlikely. I know LEDs are more efficient, but not that much more, and
the tube is consuming 60w.

What's going on? Lies?

The same lies as the 12v amplifier I bought last year. Claims 500 watts,
utter piffle i'd rate it at 5 Watts which was perfect for my
application.

I love it, 'Peak music power' and both channels added together. ;-)

Otherwise known as 'Sinclair watts'.

--
My posts are my copyright and if @diy_forums or Home Owners' Hub
wish to copy them they can pay me £1 a message.
Use the BIG mirror service in the UK: http://www.mirrorservice.org
*lightning surge protection* - a w_tom conductor

On 2 Jul 2018 17:14:44 GMT, Bob Eager wrote:

On Mon, 02 Jul 2018 15:15:56 +0100, T i m wrote:

On Mon, 2 Jul 2018 13:51:07 +0100, Muddymike
wrote:
snip

The same lies as the 12v amplifier I bought last year. Claims 500 watts,
utter piffle i'd rate it at 5 Watts which was perfect for my
application.

I love it, 'Peak music power' and both channels added together. ;-)

Otherwise known as 'Sinclair watts'.

Or Amstrad or many others sold on the markets. ;-)

Even the amps sold as '20W RMS' wasn't much use less they gave you
into what speaker impedance?

Cheers, T i m

My experience of decent LED torches which run on one 18650 battery is that they get very hot when outputting 1,000 lumens and run for less than an hour so 6,000 lumens sounds distinctly dodgy.

On Mon, 02 Jul 2018 18:54:56 +0100, T i m wrote:

On 2 Jul 2018 17:14:44 GMT, Bob Eager wrote:

On Mon, 02 Jul 2018 15:15:56 +0100, T i m wrote:

On Mon, 2 Jul 2018 13:51:07 +0100, Muddymike
wrote:
snip

The same lies as the 12v amplifier I bought last year. Claims 500
watts,
utter piffle i'd rate it at 5 Watts which was perfect for my
application.

I love it, 'Peak music power' and both channels added together. ;-)

Otherwise known as 'Sinclair watts'.

Or Amstrad or many others sold on the markets. ;-)

Amstrad wasn't around when I was selling the Sinclair stuff!

And then there's the 'Tokyo second'. Longer than the standard second.
Used to market dot matrix printers in the 1980s.


--
My posts are my copyright and if @diy_forums or Home Owners' Hub
wish to copy them they can pay me £1 a message.
Use the BIG mirror service in the UK: http://www.mirrorservice.org
*lightning surge protection* - a w_tom conductor

In article ,
T i m wrote:
On 2 Jul 2018 17:14:44 GMT, Bob Eager wrote:

On Mon, 02 Jul 2018 15:15:56 +0100, T i m wrote:

On Mon, 2 Jul 2018 13:51:07 +0100, Muddymike
wrote:
snip

The same lies as the 12v amplifier I bought last year. Claims 500
watts, utter piffle i'd rate it at 5 Watts which was perfect for my
application.

I love it, 'Peak music power' and both channels added together. ;-)

Otherwise known as 'Sinclair watts'.

Or Amstrad or many others sold on the markets. ;-)

Even the amps sold as '20W RMS' wasn't much use less they gave you
into what speaker impedance?

They're still at it in the ICE industry. Quoted power output usually about
4 times the RMS into 4 ohms.

--
*I will always cherish the initial misconceptions I had about you

Dave Plowman London SW
To e-mail, change noise into sound.

On 02/07/2018 15:15, T i m wrote:

I love it, 'Peak music power' and both channels added together. ;-)


and when driven to 100% total harmonic distortion!


--
mailto : news {at} admac {dot} myzen {dot} co {dot} uk

In article ,
GB wrote:
I was just looking at this head torch, which claims to output 6000 lumens.

https://www.amazon.co.uk/gp/product/B078NCZ6KC?

That exceeds the output from a 5 foot fluorescent tube, which seems
unlikely. I know LEDs are more efficient, but not that much more, and
the tube is consuming 60w.

What's going on? Lies?

What it doesn't say is the battery life on full power. It says 4 hours
from a couple of 18650 batteries which will be 3.7v and around 2500 mAhr.
Which suggests about 5 watt consumption then - perhaps one of the smaller
LEDs.

--
*Depression is merely anger without enthusiasm *

Dave Plowman London SW
To e-mail, change noise into sound.

In article ,
GB wrote:
I was just looking at this head torch, which claims to output 6000 lumens.

https://www.amazon.co.uk/gp/product/B078NCZ6KC?

That exceeds the output from a 5 foot fluorescent tube, which seems
unlikely. I know LEDs are more efficient, but not that much more, and
the tube is consuming 60w.

What's going on? Lies?

What it doesn't say is the battery life on full power. It says 4 hours
from a couple of 18650 batteries which will be 3.7v and around 2500 mAhr.
Which suggests about 5 watt consumption then - perhaps one of the smaller
LEDs.

--
*Gun Control: Use both hands.

Dave Plowman London SW
To e-mail, change noise into sound.