Using fresnel lenses

[leafminer]

I discovered an old fresnel lens - this is the type that are made out of a thick plastic sheet engraved with ridges. The one I found is 6" x 4" (rectangular).

Out of curiosity I experimented with placing it over one of the 150 HPS lamps. Good results! If the lens was placed very close - almost touching - the bottom of the lamp bulb (vertically mounted lamp) the lens concentrated most of the light into a beam and also reduced the amount of heat at the plant, it seemed to act as a heat filter. I noticed the brightness at the plants increase; there was much less spill.

These lenses are very cheap and after this experiment I am planning to rebuild one of my lamps as a remote ballast unit with horizontally-mounted bulb and a reflector with fresnel lens. I calculate that using the lens should allow reduction of the reflector depth to just a few inches and at the same time produce a well-focussed beam of intense light. If I could make the lens distance adjustable I should be able to change the illuminated area without raising or lowering the lamp.

[blancolighter]

YUea, I remember having one of those lenses when I was a little kid and using it to start all kinds of fires aiming the sunlight through it. Ibet you could def do some cool stuff with it growing.

[umbra]

You're gonna burn your plants

[smokingjoe]

What's that burning smell?

[leafminer]

I'm not going to focus the light to a spot; the idea is to create a defined area of light rather than having it spill all over the place like it usually does. Just basic physics. . . a reflector and a lens are both concentrators of light. The reflectors I am using right now cause problems by focussing the lamps too much, I get a hot spot in the centre that does burn the leaves.