Post by firstname.lastname@example.org
I am looking around for a best combination of leds to illuminate my planted aquarium. I was looking for some mid/low power SMD leds (< 1W) since those used to yield better efficiency, less heat and thus less cooling equipment, while being suited to my moderate lighting need (freshwater plants require less light intensity than corals). To my surprise, when i browsed the web page of a prominent lighting led maker, ranking all their led family by efficacy, the most efficient appear to be the most powerful ones: 5W upward to 30W, peaking at 140lm/W and they are white leds, are those figures realistic ? Does it still make sense to choose under driven low power leds to achieve best efficiency ?
I am seeking to combine red, blue and white leds to obtain the optimal photosynthetic spectre while keeping a good colour rendering to human eye. How to choose the best efficiency for coloured leds since, as far as I know, the efficiency expressed in lumen/w depends on a convolution function of the own power spectral distribution curve of the subject led with a somehow idealistic human eye friendly power spectral distribution curve, so that blue or red monochromatic spectres generally have poor lumen efficiency.
You do not want to measure efficiency in lumens/watt but in watts/watt within the PAR spectrum. Apparently the most efficient LEDs are blue which are up to 53% efficient. White LEDs are phosphor coated blue LEDs. You can buy similar LEDs with special phosphors for plants from Chinese Ebay stores, e.g., http://www.ebay.com/itm/10pc-1watt-full-spectrum-led-chip-1w-400nm-840=
There is just enough green in these so that plants look green. Initially, the lights look purple but, after your eyes get used to them, more of a warm white. Anyway, it's not going to cost you a fortune to find out.
They may be tuned for plant growth, but plants don't want or need
full spectrum lighting for growth - chlorophyll can only use 680nm
and 700nm for energy generation used in plant growth, and blue is
used to trigger phototropism (growing towards the light). Light
inbetween these is not useful, which is why plants look green - they
don't want the green light. No spectrual distribution of the LEDs
is given to justify the claims of plant growth or full spectrum
(indeed, the two terms are fairly mutually exclusive).
Furthermore, when you see the term 'full spectrum' in a lighting
description, think 'snake oil', as it's such an abused/misused
term in the less professional side of lighting advertising
(usually being confused with high colour temperature, which again,
plants don't want).
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