Cool! How long do those solar lights keep up those readings?
My plan is to use the solar battery pack and LEDs separately, but it looks like the pack uses 3x NiMH AA batteries in series, probably about 2000 mAH each, and the LED driver draws about 110 mA, so a rough guess would be somewhat less than 18 hours on a very full charge. I haven't measured the output of the solar panel so I couldn't say how long they take to charge. I just left mine sitting in the sun all day and crossed my fingers....
So what is the vertical scale?
, "a measure of the intensity, as perceived by the human eye, of light that hits or passes through a surface.....equal to one lumen per square metre."
So are the ones higher on the scale better for growing plants?
The lamps with higher numbers put out more light. I didn't take into account color spectrum (I also have the colorimeter head, so I may play with that later). My guess is most of the LEDs will have approximately equivalent spectra so brighter=more growth. I couldn't really say how the LEDs would compare to the CFL and Halogen though.
Would that be considered high light?
Good question. I'm not sure how to convert yet. I may try to get some PAR readings also to compare. Until then I found this (no idea how accurate it is):
Some simple data that I collected from a source:
500 lux : Cryptocoryne nevii, wendtii, afinis, java moss
500-1000 lux : anubias nana, aponogeton madagascariensis, echinodorus sp, sagittaria sp
1000-1500 lux : aponogeton sp, bacopa caroliana, egeria densa, ludwigia sp, marselia sp, ceratopteris thalictroides, java fern
1500+lux : cabomba sp, hygrophylla poliserma, limnophila aquatica, myriophyllum sp, riccia fluitans, vallisneria sp
2000+ lux :cabomba furcata, rotala macrandra
9000-14,000lux : succulents
10,000-15,000 lux : young trees
50,000-60,000 lux : cereals
But the second one I bought, the light isn't as white. I'm not sure why.
LED efficiency and color are notoriously dependent on manufacturing tolerances. More expensive brands/models (e.g. Cree) actually measure the output of each individual LED and separate them into "bins"
so you can get the same output from a set of LEDs for a given input. This is very important in architectural lighting to keep a bunch of LEDs, all driven with a similar input, from looking wildly different.
I doubt Ikea uses expensive binned LEDs in these cheapo lights, so they will vary in color and intensity from one lamp to the next.
Given Hoppy's 61:1 Lux to PAR conversion (plus X1.1 for water correction), here's the chart for PAR at 8":