I want to measure the effect of changing the supply voltage on the illumination change from the LED strip. This experiment will indirectly continue another investigation: “Why is a 24-volt LED strip better than a 12-volt power supply”.

Test bench

I took a few LED strips of different types and different power to compare the change dynamics:

- sample 1 = 2216 chips; 7.01W/foot

- sample 2 = 2216 chips; 3.66W/foot

- sample 3 = COB; 1.83W/foot

- sample 4 = 2835 chips; 4.39W/foot

(Learn more about samples)

The LED strip is mounted on a vertical heat sink and emits light sideways.
The detector/sensor is 1 foot away from the strip.

I measured the illuminance with my new high-precision instrument - spectral & illuminance analyzer HOPOOCOLOR OHSP-350MF. Total accuracy of illumination ±4% (for 1000 FC).

By comparison. My old lux meter (good quality) has an accuracy of ±3% rdg ±3% f.s.
What does this mean?
For measured value 1000 FC:
±3% rdg = 3% of 1000 FC = 30 FC
±3% f.s. = 3% of 4000 FC (full scale) = 120 FC
Total = 150 FC = 15$ strong  for 1000 FC.

Many manufacturers don’t specify full-scale accuracy. Their instruments will appear to be very accurate.

Measured values

I measure the illuminance every time I decrease the voltage by 0.1 V.
The values obtained have some scatter, related to the instrument accuracy, the measurement method, and other details. I additionally introduced a trend line to simplify the perception of the results.

Also, for simplicity, I made additional calculations of the relationship between illumination and voltage (in %).

Conclusions

1. The change in supply voltage has a linear effect on the change in light emission from modern LEDs and assemblies.

2. The light emission change from the supply voltage depends on the LED type and strip design (LED connection scheme, section length, resistors, etc.)

3. The light emission from the LEDs decreases faster than the supply voltage decreases. My samples of LED strips with voltage supply showed the following results:
3a. 2216 chip strips: 5% voltage = 20% illumination and 10% voltage = 40% illumination
3b. 2835 chip strips: 5% voltage = 12% illumination and 10% voltage = 26% illumination
3c. COB low power strip: 5% voltage = 36% illumination and 10% voltage = 70% illumination.

Warning. Other strips will give different results.

4. Incorrect connection of long LED strips to the power supply will significantly reduce the level of emitted light (due to the high self-loss on the LED strip conductors). (see conclusions to the post “Why 24V LED strip is better than 12V?”
Catastrophic effects will be for powerful low-voltage (5-12V) LED strips.