How to make a light flow meter for 87 rubles

LED lighting has become firmly established in our lives, LED light bulbs are already sold even in grocery stores, and on the shelves of household and construction supermarkets LED lamps are even larger than conventional incandescent lamps and compact luminescent (energy-saving) combined.


Unfortunately, manufacturers often deceive buyers, pointing to packaging heavily inflated luminous flux and the equivalent of a filament lamp. You buy a lamp that says “600 lumens, the equivalent of a 60 W incandescent lamp,” bring it home, turn it on and realize that it’s shining dimmer than a 60-watt incandescent lamp. Fortunately, under the law on consumer rights, LED lamps can be returned to any store within 14 days (and in many hypermarkets and for 30, 60 days and even a year). The return is possible due to the fact that light bulbs (including LEDs) are still not considered a complex technical product.

In order to understand how much light a lamp gives in reality, it is necessary to measure its luminous flux. Usually, expensive laboratory equipment (goniophotometers, measuring integrating spheres) that costs tens of thousands of dollars is used to measure the luminous flux (the total amount of light that the lamp gives). I propose a method that allows you to accurately measure the lamp’s light flux by spending only 87 rubles.

The main problem in measuring the light flux is the uneven brightness of light in different directions for different types of lamps. Some lamps shine more forward, some shine more sideways, some almost evenly shine in all directions.

For measurement it is necessary somehow to obtain the average value of the lamp brightness. Usually, for this purpose, the lamp is placed inside the integrating sphere covered with a super-white matte barium sulfate paint. Light is repeatedly reflected from the walls and hits the sensor. The goniophotometer rotates the lamp in a horizontal plane, makes a lot of brightness measurements at each point of rotation and calculates the total amount of light that the lamp gives. We will do simpler.

We need a lamp with a ball-shaped frosted plastic hood. This matt cover will average the brightness of the lamp’s radiation in different directions. Such a lamp can be bought for 87 rubles in the shops of Leroy Merlin. In the picture there is another lamp with a glass ceiling – do not pay attention: in the shops are what you need.


The lamp for 87 rubles

The exact name of the lamp – “Luminaire NBB-60 (direct base) ball plastic, white”, the manufacturer of “Axiom” Ltd., Moscow.


Lamp with a lampshade removed

As a brightness meter (Luxmeter), you can use almost any smartphone on Android. Most smartphones have an ambient light sensor (located above the screen), which is used to adjust the brightness of the screen depending on the ambient light.

There are many luxmeter programs in the Play Market, I recommend installing a simple and convenient Sensors Multitool program. After starting the program, go to the Light tab and see the light value. Luxmeter for all smartphones is not calibrated, and it will show different values ​​for different smartphones, which may differ from real ones in half, but this does not affect the accuracy of our measurements.

We fix the lamp on any surface (I used a piece of plywood). The smartphone is attached with two elastic bands to a bag of milk or juice.


Fastening the smartphone

For measurement we need a reference lamp. I recommend using the IKEA 600 Lm 303.059.76 LED1466G9 lamp. This lamp has a luminous flux that exactly corresponds to the claimed one, and a very small scatter in the light flux in different specimens.

Of course, one can also use a conventional incandescent lamp, but it is important to remember that, firstly, the light flux of incandescent lamps depends very much on the voltage in the network, and secondly, different copies of lamps produced by Russian and Belarusian plants can vary greatly in terms of Light flux. Nevertheless, you can always find out whether the LED lamp produces more or less light than the incandescent lamp.

We tighten the plafond, turn on the lamp, place the fixed smartphone in front of the lamp, start the program. We calibrate our measurement system: move the package with a fixed smartphone so that the smartphone’s lux meter shows exactly 600 lux (if we have a 600 lumens as a standard). Now unscrew the reference lamp and screw in the lamp, which we want to check, without changing the distance between the lamp and the smartphone. The smartphone will display a value that corresponds to the light flux of the lamp being measured.

I tested this simple measuring setup on seven lamps with a light flux of 200 to 1000 lm and two smartphones – the Sony Z3 Dual and the ZUK Z1. The accuracy of the measurement was 1-15%.

LED lamps have one feature – as they warm up their light flux is reduced by 11-12% within half an hour. We measured the lamps immediately after switching on, but since the reference lamp was cold, our entire measuring system was more or less accurate.

You can increase the accuracy of the measurement if you use any luxmeter instead of a smartphone. Suitable even the cheapest Chinese, for $ 10. It can be poorly calibrated, but this will not affect the accuracy of our measurements. The reference lamp and those lamps whose luminous flux we want to measure, it is better to warm up for half an hour. The luminometer must also be rigidly fixed and positioned at such a distance from the luminaire that it shows exactly as many lux as the lumens give the reference lamp.

I measured the luminous flux of the same seven lamps using a luminescent luminaire.


Measurement with a luximeter

The accuracy of the measurement became significantly higher – an error of only 0-3%.

I note that all official accredited laboratories also have discrepancies in the measurement. In the picture below, the results of measuring the luminous flux of the same lamp in 54 different laboratories. On average, the discrepancies were 3%, maximum 26%.


Results of measuring the luminous flux of one lamp in 54 laboratories

So, “on my knee,” I was able to achieve the accuracy of measurements, which not all labs can boast of.

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