Revised Selfbuilt beam intensity measures: new NIST-calibrated Extech EA31 lux-meter

[Mr Floppy]

Sorry to bring back this thread but I was just wondering about what the raw lux reading is in your lightbox tend to be?

Basically, I am making a "milk carton" lightbox (which I assume is 2 litres? We don't have milk in 2 litre cartons but fruit juice comes in 2 litres).

I'm building a light meter using TSL2561 ambient light sensor from Adafruit and a Raspberry Pi. The problem is that the TSL2561 only goes up to 40,000 Lux so some of the higher powered lights may be over that in the box I'm guessing?

 

[selfbuilt]

Sorry to bring back this thread but I was just wondering about what the raw lux reading is in your lightbox tend to be?

To be honest, if I were starting out today, I wouldn't recommend the milk carton lightbox approach (which was common when I started). Although I was able to calibrate my lightbox to estimate lumens (based on my fairly extensive dataset and comparators), it is not starting out with the best tool. While a sphere would be better, I am personally intrigued by the twisted PVC "tube" designs people are experimenting with today. Whatever method used though, you will need to develop your own calibration standard (i.e., none of the home-made contraptions are going be properly linearly integrating over all ranges).

In terms of the raw lux measures, 40K range should be fine. Due to the fact that the sensor is only receiving indirect reflected light (i.e., in any design, the emitter should not be "visible" to the sensor), even heavy output lights are well below that (with most designs).

 

[Mr Floppy]

Whatever method used though, you will need to develop your own calibration standard (i.e., none of the home-made contraptions are going be properly linearly integrating over all ranges).

The main reason why I was going to go a milk carton was to try and get as close to your set up and calibrate off your numbers as I have a subset of the lights you have tested. In the past I've tried other homemade designs, including sphere type ones, tents, cardboard boxes, eskys, but my graph points stretch and curve away from yours way too much. I know it wasn't going to be linear but at the high output end, they curve!

Cheers for the confirmation of the raw lux numbers. It saves me from having to build an ADC as the sensor above has one built in.

 

[selfbuilt]

Ah, well, then you should definitely see my comments on the lightbox design that I use (on my Methods page). One thing I may not have mentioned - I modified Doug's original design from flashlightreviews.com to have my lights enter from the bottom of the carton, with the sensor located on the side just up from the base. This way, the light's own bezel acts a baffle, and I have various size cut-outs that I use to surround the bezel (and prevent too much light from escaping back out of the box). This arrangement facilitates my ability to automate runtimes easily, since the light lies on the ground.

 

[Mr Floppy]

One thing I may not have mentioned - I modified Doug's original design from flashlightreviews.com to have my lights enter from the bottom of the carton, with the sensor located on the side just up from the base. This way, the light's own bezel acts a baffle, and I have various size cut-outs that I use to surround the bezel (and prevent too much light from escaping back out of the box). This arrangement facilitates my ability to automate runtimes easily, since the light lies on the ground.

I did notice that and I've done the same thing. The only difference is that there is a pouring hole at the other end that I have taped over and painted the inside white to get it as uniform as I can. I didn't realise that you lie the light on the ground though. So the cut outs are not in the centre? Just wondering about that as I was considering various holders and platforms to raise the light to the centre of the light box.

 

[tobrien]

very nice Selfbuilt. Your reviews are always great and most importantly consistent. I appreciate the time you take on them.

consistency is key and selfbuilt never wavers

 

[Capolini]

Good job! You are a hard working, giving and dedicated Man! Before I joined here I would see your reviews when I "googled" one torch vs. another.

I can see that your accuracy has improved with your new equipment! I have a Jetbeam BC-40 and your revised ratings are very close to theirs

My other Three great lights are the original TK-75 and the "New" TK-75 [I think I am crazy!!] which I just got today, and the Black Shadow Terminator[newest one].

Keep up the good work!!

p.s. when I get a job, I will gladly contribute to your battery fund. I need one soon!! Buying flashlights without a job is not too logical! Nor is it conducive for a good relationship with the wife!! Don't tell the Wife!!

ciao,,,,Roberto,,,,"Capo di Capo"