Inside lighting requirements plus plant color, and watering

[Matorchid]

Hello all,
Hope all of days are going well! I a few questions to ask, and I will get right to it.

When installing flourescent fixture, what should the color intensity be? Warm, daylight, reveal, cool white?. I just purchased and installed a couple of 2lamp fixtures, and got 2 32w 4ft T8 lamps for each fixture. Each lampis supposed 2750 lumenes, color rendering index of 78 (pretty poor), and color temprature of 6500k. Now I think the lumens should be fine for the oncids, right, cause they like roughly 2000-3500lumenes, is this color ok or should it be something else? I just harken back to some of my growing days where the orange (HPS)was better suited for flowering production, all the while noticeing that the lumens drop significantly on said grow lamp. How does one calculate the amount of lumens a certain one needs for a specific genus.
2 I understand what happens to an orchidwhen it doesnt receive enough light, ie. Dark green maroon underside, but doesnt this show as Mg. deficiency as well, which brings me to my next question, How does one use the epsom salts in a way that doesnt harm it? (Ratio to water mix)
And lastly I have been reading about lava rock alot lately, and really couldnt find the answer about the different colors of lava rock, does the red have a different specific gravity or less mass, than say black, or grey? Is it more porous?
So that was basically it. Any input would be most beneficial, as well as any added advice ideas

Thank you for visiting my thread and the wisdom you have given me.

[tropterrarium]

Regarding color temperature, depends what you want. Some grow orchids under blue and red LEDs but have no clue what the plants look like. Others, myself included, would like to look at the plant under "normal" human light. I use full spectrum grow lights. I would also rather go for T5HO rather than T8.

Re light output, it depends what you want to grow. Additionally, light intensity is reduced by the square of the distance from the light source. I would keep a bit of safety distance between lights and plants so that the plants won't burn from heat. I think about 8" is sufficient.

Last, but not least, consider that most turn bulbs on to close to full output, then turn them off again at night (after 12 h). Accordingly, you can reduce the amount of continuous light by half as compared to the recommended max light intensity usually found on cultivation sheets. The reason is, that natural light intensity has a parabolic intensity curve over the course of the day, whereas on/off is a square function. Once you do a bit of math, you get the same area if the grow light intensity is about half of peak natural. This first approximation works fairly well.

I explained that in one of my articles:
Geiger, D. L., 2012. Orchids under glass. A custom terrarium with bells and whistles. Orchids 81(1): 32–43.

[Matorchid]

Thank you for your reply Tropterrarium,

So color makes No difference, it just an appearance to the eyes! When I was looking at lamps there was a direct correlation between color and the amount of lumens, isn't the objective to have as much light available to the plant when it wants it.
Other than energy savings what's the difference between a T5 and T8 setup?

Thank you for the info

[Ray]

The ideal light for all plants is one having a color temperature of about 6500°K, as that mimics direct sunlight at noon on a summer day, supplemented with the blue back-scatter of the sky - in other word, what nature provides (and what they evolved to use).

The problem with fluorescent and LED lamps is that the color temperature is expressed as CCT - correlated color temperature - where the "correlated" means "looks the same to the human eye", not that it has the same spectrum. Most commercial T5HO plant light bulbs have a CCT of 6500°, and use phosphors designed specifically to support good plant growth and flowering.

T8 bulbs were designed to be energy-saving, drop-in replacements for old T12 "shop lights". In a 4' lamp, a T12 consumed 40 watts, and put out about 40 lumens/watt, or 1600 lumens. The energy-saving T8 for that fixture was 32W, and put out about 90 lumens/watt, or 2880 lumens. A 4' T5 HO plant light not only gives you a great spectrum, but at 54W & 90 lm/W, gives you 4860 lumens to work with.

[tropterrarium]

Color does make some difference. If you look at spectra of cool white, …. vs. full spectrum, you will see very narrow peaks with cool white, …. whereas full spectrum have a wider, gentler curve, more like the ideal black body radiator. Matching light wavelengths emitted from light source to what plants require (i.e., absorption spectra of chlorophyl and xanthophyl pigments) may be very hard, if not even impossible if you grow more than one species. That matching is the idea behind the red/blue LED growing; note that LEDs have a much broader spectrum than the peaks of typical house hold fluorescent tubes.

T5 also have a higher overall light output. So if you want to grow high light species (Vandas, Cattleyas) as opposed to shade plants like pleurothallids, you may have better luck with T5HOs.
T5s require different fixture from T8. There is plenty of discussion on T5s etc. both in the "grow under lights" section as well as in the "terrarium" section. Do some searching and reading there.