HELP! light fixtures

[KoolKat]

I was using my lux meter to get best light levels from 600W HPS. Found a hot spot that's 80K lux while colas right under light get 60K. This light fixture SUX! Does anyone know any tricks to diffuse hot spots and allow closest light positioning? I was looking at SOLAS reflective tape. That failing what's the best air cooled fixture for single 600W bulb?

Also what is the best HPS bulb?

Thanks folks

[DrPhoton]

Light uniformity is difficult with light sources that are small. Light behaves like electromagnetic waves and the characteristics of light through space, exhibit wave light propagation. When energy is emitted from light sources with a small surface area, such as from a sodium bulb or LED, light will diverge with low uniformity with respect to the horizontal plant canopy.. This is because of the geometry and size of the source with respect to the observation points.

Reflector hoods are a way of utilizing the light from light sources where light is emitted in wide angles. By using reflective material or optics, the light that would otherwise be directed away from the desired area is directed towards it. Allowing the maximum use of the light source possible. This applies to both old and new technologies where either reflective or optical products are used to control the direction of light.

With reflector hoods on gas discharge systems, there are many design choices that are used to help decrease hot spots and provide better light uniformity. Such as multiple reflective points, diffusive surface geometry, size etc. But this can only do so much, as the potential for improving the uniformity through light reflective means is ultimately limited by the size and shape of the light source. With gas discharge sources using reflective hoods, the best quality designs are those that implement the previously mentioned properties with size being the major difference between designs. The larger they are, the more light can be spread out evenly. The best measured hood for uniformity and performance is the XXXL dominator.

To improve uniformity further, you either have to do one of two things. Either match the shape of the plant canopy to the geometry of the light source or match the geometry of the light source to the canopy. In our case it is more practical to do the latter. This is done by increasing the surface area of the light source. With gas discharge this is not possible because the whole technology design relies on the concentration of energy to reach optimal temperatures. LEDs however are able to be designed to increase the surface area that light is emitted from and match the geometry of the plant canopy. Such fixtures that do this well are the nextlight mega LED and fluence spydr X. The large surface area allows superior uniformity and proximities as close as 12".

With all that said. When talking about light proximity with typical light sources. The main concern is balancing the light source proximity so that light is not attenuated through radiative and reflective losses by having the fixture too high. But also making sure energy is not lost through having it too close and reducing the photosynthetic efficiency through photochemical quenching and other quenching mechanisms that channel excess light energy that cannot be processed. With my research on light technology and plant science. I have calculated that the best height is when the center square foot is at around 80,000 lux in a 4x4 with a 600w source (does not apply to differnce sized sources and grow areas. Any higher or lower and you introduce losses that deteriorate the light utlization efficiency.

[KoolKat]

Thanks for the feedback. I was an ET in a physics dept. so I am following your argument. When this crop is done I plan on making a crude 2D map to see what I have at three or four distances across a 3x4" area. Maybe 25 measurement points if I'm inspired enough. I think you'll likw what I've done so far with reflectors and a socket extension. Please see my latest post for details and photo's.

[KoolKat]

I've made 2 changes to my light fixture. 1st I discovered that I have a 1,000W fixture in a 600W setup. So I added an extender (Lutron) to the mogul socket. This helps center the bulb but also causes the bulb to droop out of level. Iwill probably rebuild the socket base post grow. 2nd I fabricated two side wings to extend the existing light fixture wings out and down. I did this by glueing some Orca film to foam poster boards, and no they didn't melt. (They don't even get warm! Orca definately works well into infared.) The way the 'wings' are mouted I can extend or retract their length to drape over my PVC trellis from different heights (more on that in another post soon). The fixture itself is pebbled metal like most, BUT directly above the cool tube it's mirror finished! I believe this to be the hot spots cause. Playing with my Lux meter I found 4 - 8 K increases at the top and better distribution through the canopy. Idid not have to move the light up - the increases were to the sides.

I am wondering if I could get away with lining the whole fixture with Orca film and/or tape. Orca is a truely awesome product, far supperior to the old glass bead stuff. The light fixture itself is well made I would cut and fit the Orca film to each pannel to retain it's shape. I'd love to see some of the projector screens this stuff must be made for. I will be calling Orca for advise soon to see if this might work. I am also interested in getting the cool tube anti-reflective coated if this is even possible. AR is really magic stuff, one of the secrets behind all the best optics.