2020 October: No kits available at the moment
Update 22.1.2020: Current calibration set consists of two Convoy S2+ with XM-L2 (low CRI, cool white) and SST20 (high CRI, neutral white). Price for the kit is the same at 67 € including two lights.
Update 14.3.2019: Interest list for a throwier calibration light (Convoy C8+) added. Only 1 piece measured and ready to go now.
After some interest from people wanting to calibrate their integrating spheres / lumen tubes I decided to make these little calibration kits available. For 67 euros you get two lights shipped anywhere in the world and you won’t have to rely on manufacturer or reviewer ratings, which might vary as much as 20% between samples even in the same batch. Read on for details.
As of 20.7.2018 I have ordered enough lights for 40 sets out of which about 20 has been tested and shipped. More will be made available as long as there’s interest and I am able to find reasonably priced suitable lights
For the calibration kit I’ve chosen the BLF348 and Convoy S2+ as they have a very consistent output (S2+ on low and mid). In my testing the output of the BLF348 stays within +/-1% regardless of the NiMH battery used between several measurement rounds. I still recommend using a fresh Eneloop or Ikea Ladda as a worn battery with high internal resistance will not work reliably. For the 7135 regulated Convoy, it doesn’t really matter which 18650 is used and the repeatability makes them perfect for calibration.
The lights have also been chosen to have different color temperature and CRI. While the BLF348 is neutral white (4500-5200 K) and very high CRI (Ra >90, R9 >80) the S2+ utilizes a cool white XM-L2 (~6500 K) with a low CRI of about 70.
This should give you two good data points to check whether your lux meter is affected by the differences in the spectrum. If the difference is large, you might want to use a different correction factor depending on the light being measured.
Total price for the kit with two calibration lights and data is 67 euros.
(PayPal will handle the conversion for you if you’re not in the EU)
First shipments should be ready to go out the door within two weeks while I wait for some S2+s to arrive.
Payment is done via Paypal (goods and services) or the equivalent amount of crypto (BTC, LTC, ETH, BAT…).
The price includes shipping anywhere in the world. I will send the lights without their original packaging padded in an envelope. This is due to the 3 cm limit for envelopes. Shipping time will be approximately 1-2 weeks to most countries. Up to 4 weeks to the remotest areas such as New Zealand.
There will be no tracking
If you need tracking the cost will be 87-100 euros depending on the country due to the high price of shipping packages from Finland.
For disclosure, the total price consists of 30 euros for the measurements and generating the data. Everything else is to cover the cost of buying the lights, shipping, packaging and paypal fees.
If you are in the EU, you can also send me your own lights to be measured. The cost of lumen measurement is 20 euros for the first light and 10 euros for any additional ones. You pay for shipping both ways. Remember that shipping boxes out of Finland is very expensive, especially if they have to be tracked.
In this case you can also request which battery should be used for testing. Do not send me any batteries. I have a wide range of 18650s.
While I already have procured some BLF348s, I’m still waiting on the Convoys. Let me know if you are interested and I’ll order more as needed.
What you get
The measurement report contains luminous flux in lumens at 0, 30 and 60 seconds as well as various measurements from the hotspot such as intensity in candelas, color temperature, tint and spectral data in image and text format.
The equipment used for calibration
The calibration lights have been measured in a 50 cm Lisun Group integrating sphere using an X-rite i1Pro spectrophotometer. The sphere was calibrated using Lisun’s SLS-10W standard light source. This is the setup I use in my reviews.
Sphere album: https://imgur.com/a/EbqM3
The problem with calibrating an integrating sphere based on a flashlight that you have and some reviewer has tested is the big differences in LED bins and driver component tolerances. After measuring 10 BLF348’s from the same batch, I found output differences as large as 15%. Same goes for a seemingly reputable manufacturer’s specifications.
The point of a calibration light is that you measure the lux from your sphere using a light with a known output and then divide the given lumen output with the lux value. This gives you the correction factor which is used when measuring other lights.
For example, you get a calibration light which outputs 34 lumens. You measure its output in your sphere and the meter reads 100 lux. This means your correction factor is 34/100=0.34 which is used to multiply any subsequent lux readings to convert into lumens. A light that reads 500 lux is 500*0.34=170 lumens.
For information on how to make a DIY integrating spheres check out threads by djozz and JoshK. The widely used lumen tube uses PVC plumbing pipe, the latest thread on the subject is by Texas_Ace, which was also later calibrated by lights I tested for TA.
Please note, that the biggest problem with these devices arise from lights that are especially floody or throwy. If your lumen contraption is not integrating the light well enough, the numbers will be too high when measuring throwy lights. This is why it’s very important to try and diffuse the light as much as possible before it exits the sphere/tube and hits the meter. Matte surfaces, baffles and diffusers are your friends.