Converting lux,lumens and foot candles

[Rhonda Svoboda]

How do i convert these light requirements into practical terms? For example, if an orchid requires 20,000-30,000 lux, what the heck is it? Bright shade, full sun?
This is not helpful or usefull information if I don't know how to use it.

[estación seca]

Lux and footcandle are two different units to measure the same thing: Amount of light striking a specific area in a specific time. Lux is the metric, or SI unit. Footcandle is the English unit.

Here is a conversion calculator:
Footcandles to lux (lx) conversion calculator

If you look at the Wikipedia article for "Daylight" you will find a table of lux at different degrees of daylight.

This is a measure of all light. There are measurements of the specific wavelengths plants can use. Natural light growers don't really need to think about this. LED growers do.

High-light orchids will still sunburn if they've been in the shade for more than 2-3 days, and you move them into sun. Light increases should be done gradually or stepwise.

[Ray]

Lumen is a measure of radiance - light output from a source.

1 foot-candle is 1 lumen per square foot.
1 lux is 1 lumen per square meter.

Keep in mind that, in addition to ES’ warning about transitioning a plant to higher light levels, such recommendations are generally an indication of the maximum noontime intensity the plant should see, not a continuous level, if grown under artificial lighting.

[Fairorchids]

And then, just to confuse the issue even more, in 'greenhouse speak', we often reference the type of shade cloth we use.

35% = it blocks 35%, and lets 65% of sunlight through. As a rule of thumb, for the indoor season, I recommed:

15-20% shade cloth for high light plants, such as Cymbidium & Vanda.

35-40% shade cloth for intermediate light plants, such as Cattleya, intergeneric Oncidiums and Phragmipediums.

55-60% shade cloth for low light plants, such as Paphiopedilum & Phalaenopsis.

[estación seca]

Shade requirement varies with your degrees from the equator. Here in Arizona people use 60% minimum on greenhouses or everything sunburns, including Vandas and Cattleyas.

[Roberta]

Not only latitude, but also growing area orientation with respect to the sun. My yard is pretty much east-west with few trees in that direction. Especially during the summer, it toasts all day. I use 60% Aluminet for all the general areas, the Cymbidium/L. anceps area uses generic 45%. An indoor area would likely need less, in part because with the shifting sun, there is some shading during part of the day - duration of the the strong light is also an important factor, as Ray pointed out.

[Ray]

For you real geeks, I highly recommend looking into a Weatherflow Tempest weather station.

Living where I do and doing a fair amount of outdoor activities, boating and fishing - and hurricane cleanup - it is good to know exactly what's happening. I replaced an "Accu-rite" system (because it wasn't) with one, and I find that, in addition to highly accurate wind, rain, pressure and lightning info, it tells you the light intensity (lux) and UV index, as well.

As of 8:20 am EDT, as I type this, we're up to 30700 lux. Yesterday our peak was 173000.

[Rhonda Svoboda]

Thanks everyone for your imput. The conversion chart and Wikipedia info is vey helpful. I don't have a greenhouse- just windows and summer outdoors. I do use LED grow lights in the winter to keep my plants alive and they worked well last year. For my purposes (novice not professional) The info provided will help a lot-