I was just looking at this head torch, which claims to output 6000 lumens.
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).
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.
I think lumens is the total amount of light coming from something, so it must be lies.
Bill
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
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...
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
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 bollocks.
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.
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.
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 candelaetc.
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
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.
I love it, 'Peak music power' and both channels added together. ;-)
Cheers, T i m
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.
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.
Oooh, what stuff did you sell? All the electronics, the kits, the C5?
I built several of the ZX81 kits (and got a load more working for others) and the Micromatic Radio. A mate built their calculator and assembled the Black Watch.
Hehe.
Cheers, T i m
Much earlier. The Micro-6, Micro-FM, Micromatic. And the PWM amplifiers, which definitely had optimistic power ratings. And didn't work well. Think that was also connected with the Stereo 25.
I stopped all that in about 1968.
Cool. ;-)
;-)
Was that down to poor design, or underspeced components (or possibly both)?
I don't remember the audio products I have to admit.
I still have most of my Sinclair computers (ZX81, Spectrums, QL) and my C5 (waiting till such things come into fashion and with all the congestion charging and low emission zones that are coming in that might not be so long now). ;-)
Cheers, T i m
Both, I think.
I only have a ZX81 that I was given. Earliest complete 'real' hardware that I have. (I have parts from the Atlas, ICL 4130, ICL 2960 ...)
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