(prototype) the GT Mini

nkresho, wondering about how you figure your lux reading… if you do it at 20’ what is the math on that? I ask because I was told to use EXACTLY 5M (or 10M or 15M or more, I’ve done up to 50M), then multiply the meter reading by 5 squared (25) to get the lux reading. So if it’s a multiplier of the distance squared, what do you use as a multiplier x meter reading? (just checking to see how you derived that lux number) 5M of course is 16.4’. It would help if we all used a standard distance, but of course throwers actually need some space to get the beam focused properly if they’re any good at being throwers, so a 5M reading may be cutting the lux short.

Using this in excel: =(0.09290304*T22*20*20)
with T22 being the cell with the lux reading.

Meter is in a dark room, in my basement, on a black metal cabinet. Meter reads 0 at test start, with ambient light.

Measurement is 20’, via tape measure to a fixed point on the ceiling, with a thumbtack and a long rubber band hanging to where I hold the light.

I test for 30 seconds and have the meter set to display the max number (this might be where i’m off). Reading peak rather than the 30s number.

I measured my GT (bone stock) at 30’, and used =(0.09290304*S21*30*30) for that one. I got 1.151M candela in that instance.

What is the 0.09290304 number? Not sure why the two lights, at different distances and power levels, would have a same multiplier…

Ok, say you’re at 16’ 4.8” distance (5M) and you shine a light at the meter which reads 10,000. You’d multiply 10,000 x 25 for 250,000 as a lux reading (250Kcd) and then take the square root of 250,000x4 for throw. (1000M throw)

Another light, weaker, shows 767 on the meter set at 10x, so 7670 x 25 = 191.75Kcd. Taking the square root of 191,750 x 4 you’d get 875.79M throw for this one. See? nowhere is there a same multiplier except for the distance squared (5M squared is 25)

I don’t know all this part well enough to understand why we’d have a different formula, which is why I’m asking. :wink: Trying to discover how we all get on the same page.

Woohoo!! Got mine in the mail last night just in time for some night work on a movable bridge. This GT-Mini is tiny… smaller in hand than expected. Slightly shorter than my Nitecore P30 (by 0.5 inches/12mm) but the head/bezel diameter is nearly the same…I put them face to face… but the head size of the GT Mini is smaller than the P30. Just got to get used to the side switch on this little bad boy (I’m used to the dual-switch on the P30- Tail for on/off with tactical momentary-on and side switch for mode/levels).

Most likely mentioned before but UI is similar or same as BLF Q8.

The only bad thing I have to say about it is that this is a minor dimple in the reflector 10:30 o’clock position (looking at LED with switch at 12 o’clock position) about halfway in between lens/bezel and LED. It doesn’t affect the output or quality of the beam but it is a minor defect. It is very noticeable because the rest of the reflector is near perfectly smooth (the lateral machine lines on the Nitecore P30 are way more noticeable). It sticks out like a sore thumb.
Is there a way to request a replacement reflector?

I’ll figure out a way to post a pic.

I wish I could see your pictures, but they are not showing up. Your sphere sounds a lot like the ones from Josh K. Is that what you have or is it just similar to it? Not the same at all.

Keep in mind that the Catapult V6 uses an xhp35 Hi which is a bigger LED than xpl Hi.

I’m guessing the 0.09290304 number is about converting feet to meters. Candela is always meters.

By far the easiest way to measure it is try to find 10 meters in your house. It doesn’t need to be completely dark or anything. Just subtract whatever the ambient light is from your total reading. I typically set my light down so that the emitter (not lens) is at the 10 meter mark from the sensor (meaning 1” from the wall). Then I turn on the light and walk over to the opposite wall and try to find the area of the hotspot that is brightest (I measure along a straight line between the center and the edge of hot spot). It can sometimes take 25 or 30 seconds, so I just kind of count that out in my head. Once you have the number at 10 meters the math becomes very easy. You take whatever that number is and multiply by 100 which is just adding two zeros to the end.

So my GT Mini was 1,480 lux. This is 148,000 candela at 1 meter. Easy math. My big GT was 10,560 @10m which is 1,056,000 cd. 10 meters is the way to go if you have the space.

Then to convert to distance is the regular X4 then square root.

Mine thrunite v6 measurement are similiar to nkresho. If that is true, mini gt cw have more lumen than nw … i was told mini gt cw led are high bin. anyone can verify ?

Here’s my formula reference:

Lux to candela calculation with distance in feet
The luminous intensity Iv in candela (cd) is equal to 0.09290304 times the illuminance Ev in lux (lx),
times the square distance from the light source d2 in square feet (ft2):
Iv(cd) = 0.09290304 × Ev(lx) × (d(ft))2

Source is here: Lux to candela (cd) conversion calculator

Sorry, hosted to imgur, since photobucket and imageshack are garbage nowadays.

My sphere is a semi-copy of the “match sphere” Started with a ~17” bouncy ball, paper mache’d it ovfer and over for a few weeks, then did a few layers of fiberglass for strength. Cut it open, sanded the inside and painted it with BaSO4. Two baffles using pingpong balls, also BaSO4 coated, were added. One to catch direct light between the source and the sensor, and a second to catch the primary reflection directly opposed to the source. It uses an interchangeable light plate similar to the newer TA tube design, so each plate can be the right size for the light and I can swap them easily. They are also BaSO4 coated. Sphere is also calibrated with Maukka lights and have a variable multiplier correlated to color temp. Warmer lights get a slightly lower multi, due to how my DrMeter reads.

I think you are making your calculations way more complicated than necessary. I would just use a simpler method such as 10 meters. There’s no need to reinvent the wheel.

It’s all in a spreadsheet. I just plug in the lux reading and it does it by itself.

I work in excel all day long at work. It’s only complicated once.

But, if it’s not accurate (the math involved), I am happy to change it up.

Very nice unit. :+1:

Thanks. She’s kinda ugly, but does the job well as far as I am concerned. Lumpy like a big black meatball on the outside. Was so sick of paper mache-ing that I didn’t really sand the outside to a body shop quality finish like I originally planned. Business end (inside) is baby-butt smooth.

I can’t understand what your saying here. Are you saying that the Mini GT cool white has more lumen than the Mini GT neutral white?
Where does the Catapult V6 fit in?

Jason, I think he’s saying that he gets similar readings as nkresho on the Catapult as a reference to accuracy, then says his mini gt with cw has more lumens than the nw which it should. Given the same power bin a warmer tint will always read lower output.

Nice work nkresho, the complication is that you are using feet instead of simply staying with meters as per the industry standard. Aside from that the calculations are the same. I really don’t see any need to convert with that 0.09 number, as distance is distance regardless what you call it. But then, what do I know? (no answer required, I get it…)

<— zip experience with spreadsheets and/or excel. :wink:

Yes … I measured my v6 with shockli.

thrunite catapult v6. 2050 @ turn on. 1970 @ 30 sec
Blf gt mini 1390 @ turn on. 1300 @ 30 seconds.

received mine (from the group buy) today!

something to fiddle with when it gets dark…

is your gt cw or?

I don’t know who posted this to make tail cap measurements one handed.

So I’m probably going to be the last person from the pre-sale to receive their light……

Had an ETA of Monday the 27th, and then when Monday came and went, it suddenly changed to stuck in customs. And all of that after the 3 week delay in China.