The "amount" of light is expressed in lumens and is determined in the lumen meter. A luxmeter is rather useful for measuring the illumination of work surfaces. And the Made in China lux meter for PLN 30, I don't know if it can be useful ... Although not - it can measure these Chinese lumens ?
lumen determines the total amount of light generated by a given light source - the measurement is made inside the ulbricht sphere. Lux is the light intensity - its quantity in relation to a given unit area. In practice, it is rather impossible to determine the efficiency of the LED diode as lm / W at home without hardware. But as I wrote earlier, if these Chinese LEDs do not have lumens, the quality of this light is still poor due to the low CRI. It's such a thing that on the one hand it hurts the eyes and on the other hand it does not illuminate the area well.
And the Made in China lux meter for PLN 30, I don't know if it can be useful ...
Of course it might be useful. Not for an accurate absolute measurement, because you would have to calibrate it with something first, but it can be as a comparative measurement device. Many measurements are made not to know the absolute numerical value, but to compare the reading with something.
For example: I have a table lit by a 4 x 18 W fluorescent lamp. The Chinese lux meter shows X. I change the fluorescent lamps to LED and the lux meter shows Y. Then you know how the light intensity has changed. A subjective impression is also important, if only because of the CRI mentioned here, but thanks to the measurements you can form an opinion whether such a change made sense.
I used these 10W LEDs to illuminate the sidewalk outside the house. They lasted 4-6 months at half the rated power. I replaced 4 of them in one lamp. 3W led bulb with a 12V lid, gouged out of the original housing and inserted into the "halogen", turned out to be many times more durable; is over 15 months old and still shines flawlessly. I did not observe the difference in brightness. All COBs are put on thermo paste and additionally screwed to the housing. Such a Chinese COB 10W cost 2-4 PLN, in lidl I paid 5.99 where the set includes a current source to power this LED. I suspect that in the case of the COB from this article, the durability will be similar. How many people have seen flashing "halogen" LEDs where the problem was the damaged COB LED.
CRI - is it the color of light? This is the first time I hear about anything like this. Until I checked on google. Generally, I once bought 25W cheap for ridiculous money. For 220 V. I wanted to convert to 12 V for the car. For now, I gave up.
In general, with light, it is not always brighter is better. Cheap LEDs have low photometric efficiency, which explains why they are cheap (they emit a lot of heat and a lot of UV). There are tests on YT and, for example, expensive Power LED 1 W can give as much "light" as cheap Chinese 3 W.
As for the measurement of light intensity, on most phones you can install the application, it is not a laboratory measurement, but by specifying the distance of the light source, it is always a reference point.