Maybe I'm confused
 

Far from me thinking that I want to insult someone.
I ask those who can clarify; what role light plays in plant life?

I think you know light is of vital importance to plants and w/out it they would die. Some quicker than others.

Not sure why you're asking though. Did I miss something?

Yeah not sure I understand the reason for the question, but quite often in our homes we can't supply the level of light that a certain orchid would get in it's native climate, in which case we need to add artificial light. Plants genetically adapted for a certain light level won't do well if not given that level of light.

It is necessary for the chemical reaction that provides 'food' for the plant. If you have had any chemistry classes, you know that some reactions require something extra to stimulate a reaction (electric, heat, catalyst....). This reaction takes light.
The plant uses the energy from this reaction to then build cells (we add fertilizer to help with this process as plants need a number of different minerals and chemicals to build cells) and fight diseases and pests. Does this help?

From what I can think of there are 4 things.

1. Photosynthesis: Convert the light energy to chemical energy, and use it for assimilate carbon from CO2
2. Photo-periodism: SOME plants use the day lengths to assess the seasonality (e.g. timing of germination, or flowering).
3. Photo-morphogenesis: plants use the quality of light to assess the environment.
4. Circadian rhythm: Like human, they do have internal clock for the rhythm, but light is used to "adjust" the clock.

#3 is a bit more difficult to understand. Plants don't have eyes, but they do have the sensors to quantify the amount of light with different wave lengths. For example, if there is excess of far red light over red light, this indicates that the plant is covered by other species because the leaves above have absorbed lots of red light. Then some plants would etiolate (i.e. make skinnier and long stems) and try to be outgrow the other species. In other words the quality of light influences the shape of the plants. For weeds growing in a corn field, this response is advantageous. But understory plants in a forest shouldn't do this (no way to outcompete spruce trees).

Similarly several aspects of plant's "shape" can be influenced by the "quality" of light, and this is called photomorphogenesis.

Thanks very much naoki, here I wanted to go.

---------- Post added at 02:36 PM ---------- Previous post was at 02:31 PM ----------


And to not get drunk with cold water must clarify what light (length of wave, etc.) influence Photosynthesis and Photo-morphogenesis.

I am also a little confused by the reason for the question, but adding to what others have stated, light provides plants with the energy required for photosynthesis (converting water and carbon dioxide into the sugars that plants need in order to live).

Without light at all, these processes don't happen and the plant dies. With insufficient light, the plant performs poorly. Too much light, and the plant burns.

I just want to understand how choosing a light source.

Natural sunlight is best, and can be reduced if needed using shade cloth (to keep sensitive plants from burning). Artificial light is fine as well, and there are many possible choices. I have not used the LED lights that are designed specifically as grow lights, but I hear the energy savings can be substantial and eventually offset the initial higher cost for the lights.

In winter, I grow plants indoors using T8 fluorescent Daylight 6500k lights. This seems adequate for my collection which is mostly Cattleya alliance and Phalaenopsis, with a few Dendrobiums and a few other genera. During the warm months I grow outdoors under shade cloth, except for a few plants which are adapted to full sun.

I hope this helps.

Nexogen, are you talking about different spectra of LED light? If you start to talk about the optimum spectrum, it is not so easy.

For a given amount of photons, red light is most efficient in terms of photosynthesis. But the plant may grow in unnatural shape. Orchids may be slightly different, but adding blue light generally makes more compact plants (photomorphogenesis part). That is the origin of Red+blue grow light. During the conversion of electricity to photons, blue LEDs are more efficient than red LEDs.

With the recent advance in white LEDs (basically blue LEDs + optical coating, phosphor, to produce white light), PAR efficiency of white LEDs could be pretty high. Within white LEDs, warmer white is slightly less efficient in conversion from electricity to light than cooler white. However, from my measurement, amount of photosynthesis relevant light (PPFD) per watt doesn't seem to be so different between 5000K and 3000K. So it probably doesn't matter too much. I generally choose 4000K or 3000K LEDs these days.

I did came across a promising T8 LED bulbs which was tested to show >140lm/W (very high efficiency, almost DIY LED level). This could be great for orchids. Once I receive them, I'll probably post something about it.