Joule Lamp

[JouleSeeker]

Congratulations, Lynx!  indeed its time for lumens/watt testing.Let me see if I can explain how easy this really is, how I'm going about it.  I would like to do these measurements, but I'm way behind you on the builds (you are fast!), so I'm going to encourage you (and all) to build a simple light box.  Here's the vid I put up just now:

http://youtu.be/XoGJ_tG2QBM

  Vid shows the "light box" I put together with my son today for these devices and how it is calibrated.
We first take one bulb of KNOWN lumens output, specified on the package and  place the bulb in the light box.  (I use the middle position on the power strip as seen in the video.) Turn the bulb on.  We note the lux as measured by the light/ lux meter.  We check that the Watts-input is close to that specified for the bulb (on the package again).   


The package on this CFL bulb says it puts out 900 Lumens (Lm) running at 13W.   
I find with repeated measurements -- when the CFL bulb has warmed up -- the light output is 10920 Lux (average).  Then, I divide:
900 Lumens/10920 Lux = 0.082 Lm/Lux.   


I repeated this calibration for an LED light, 600 Lumens running at 9.5 W is seen from the Light Box as 7280 Lux, again 0.082 Lm/Lux for this light box.  (Each light box will have its own conversion factor, Lm/Lux, which can be calibrated in just this way.)


Repeated for a 60 W bulb, 850 Lm / 10760 lux observed = 0.079 Lm/Lux.
Repeated for a 40 W, 75 W, 90 W and 100 W incandescent bulbs also, the average is about 0.080 Lm/Lux +/- approx 6%. You can just use 3-4 light bulbs for calibration. Close enough to really help us in this research!


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So I put in a second bulb (done with incandescent and CFL) in the front position, and got very close to the same 0.080 conversion factor. That is, the second bulb DOUBLED (very close) the lux light output on the meter.  When I put a bulb in the back position (near the switch on the power strip), the conversion factor was about 0.085 showing that a bulb in this position gives a non-linear response; which is OK with this separate calibration for the two bulbs in these positions.

For three CFL bulbs, in the three positions with adapters as seen in the vid, I found:

2700 Lumens / 29600 Lux on the meter  = 0.091
(a larger conversion factor as I expected, because less lux reaching the light meter with three bulbs in this configuration)

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Now that the box has been calibrated, we can place an UNKNOWN light source into the box in the same spot, or two  or three light sources in the locations described, and measure the light output in Lux on the meter.  Then,
Lumens output = 0.08 * Lux (for one bulb,as read on the meter). 

For more bulbs, would use the appropriate calibration factor we have determined... Easy!

Finally, we determine the input power (if from a battery and DC, P = I*V, current times voltage), and calculate Lumens-out per Watts input -- Lm/W.


  The idea is to MAXIMIZE Lm/W in various test devices, such as Lasersaber's SJR 2.0, and Lynxsteam's Teslamp.  (Great work, gentlemen!)  I strongly recommend use of a light box for quantitative measurements of Lumens-out/Watts-in so we can make solid scientific progress. 

For comparison, we calculate a few known values from bulb packages:
Incandescent, e.g., 850 Lm for 60W bulb => 14 Lm/W
Fluorescent, CFL, e.g. 900 Lm for 13 W bulb => 69 Lm/W
LED, e.g., 600 Lm for 9.5 W bulb => 63 Lm/W.


I strongly recommend use of a light box for quantitative measurements.

  A value above  100 Lm/W would be very interesting!  Let's see what we can come up with.   

[JouleSeeker]

Attached shows the light meter I used...  Cheap and good! from Amazon.
Input power meter was useful also, monitors input power if 120V 60 Hz -- from ebay, see attached.

[JouleSeeker]

PS -- size of the box doesn't matter too much; needs to clear the lamps by a few inches at least (temp concerns).

I was looking for a Xerox box, removable lid would be nice.  Found a tall box with top flaps -- works well.
Size of box will affect your calibration factor, which you get from measurements from bulbs with known-lumens (see posts above). 

Smallish holes admit wires for power-strip and light-meter as needed.  Took my son and I about 20 minutes to build this morning.

[Lynxsteam]

JouleSeeker,

Great work on the Lightbox.  There is a lot of ambiguity when experimenters are quoting brightness.  Words like "fairly bright with just 600 ma" is pretty loose science.   I always start with loose science to get in the ballpark quickly and then circuits and methods need to be tuned.  I will be happy to send you a 25 watt DC converter as I have built.  It would be great if you would test it for efficiency.  You have spent the money on the Lightbox, no need for us to both duplicate.

There are simple ways to tune the Lynx Joule Lamp circuit without bleeding power through resistors.  Today I will do a video showing how a small 12 v solar panel can easily power LED bulbs. 

[b_rads]

 
Got my LJL (Lynx Joule Lamp) put together last night on a test board and it works.  This replication was built as near the same specs as Lynxsteam showed.  Running off 12 Volts, I can adjust the current to just below 100 mA and up to 400 mA.  The interesting thing I noticed, when started at 400 mA and allowed to warm up, I could drop the current to 200 ma without any observable degradation in light output.  Below 200 mA and the light gets considerably dimmer.  Using the taps, the minimum number of winds that the light would start up was when the current was highest and the bulb the brightest.  Increasing the number of winds lowered the current draw and the bulb got dimmer (sounds crazy huh).  Next, I need to chart the taps and current draw and graph out to see how this is working.  Thanks again Lynxsteam for the wonderful plans and vids that made this a relatively simple build.

Brad S