Beware of the ridiculous power ratings on solar lights


The Sunday Nation


30 July 2023


Marketers of consumer products always use the word “power” to cheat and confuse prospective customers. Be it motor vehicles (where I have explained in a past article that power is meaningless to a driver) or music system (where I have explained in the past that the quoted figures are mostly total nonsense).

It appears that this madness has moved on to lighting equipment. I recently saw a solar powered security light labeled “200W”. The solar panel supplying it with electricity is about 30cm long and 15cm wide. That is, it is about 0.045 square metres.

Now, on a clear, cloudless day, the sun’s energy arrives on earth at a maximum rate of about 1,000W per square metre. Thus, if this solar panel was 100 per cent efficient (in reality it is nowhere near that), it would generate only 45 watts of electricity. So, I wondered: where does the solar light get 200W from?

If we take the real efficiency of about 15 percent into account, it turns out that the solar light can only capture about 7W from the sun – at noon on a clear, cloudless day. Even though I did not get a chance to inspect the technical specifications of the gadget, I highly suspect that the solar panel is rate at 5W(peak).

Let’s add another reality: the morning and evening sun are not as intense as the one at noon. For that reason, the average performance of solar panels (on a clear cloudless day) is about a half of the rated peak. Thus, in this case it is about 3.5W – yes; three-point-five watts! What kind of magic is being used to get 200W from a mere 3.5W?

The only way this is possible is if the panel is exposed to sunlight for 57 hours and then switched on for just one hour. But if the light is expected to remain at full brightness throughout the night – from 6pm to 6am – then it should be charged in the sun continuously for 57 days!

It appears that the stated 200W is complete, utter, absolute, diabolical nonsense! On second thought, however, could it be that the manufacture is stating the incandescent equivalent brightness?

Well, a Light Emitting Diode (LED) produces about 10 times the brightness of a hot filament for the same power consumption. Therefore, a 200W incandescent lamp would generate the same light as a 20W LED. Still exaggerated; still ridiculous!

  Back to 2023 Articles  
World of Figures Home About Figures Consultancy