{{gwi:173755}}This is the one I use and it is inexpensive, only about 20 dollars. It is accurate enough for growing orchids where the approximate light level and relative light levels are important.

I just have to remember to dust off the top once in awhile, that is where the sensors are.

To follow up on Richard's post. The only source I found when I looked a few years ago was at Planet Natural.
Click here

It is a great little device and covers the most important ranges needed for orchids. Measuring outside light is problematic as it tops out at 5000 fcs.

>> does the light value increase the longer the lights are on?

To some degree, you can compensate for lack of intensity by increasing the duration.
This varies from plant to plant, but on average should work.

There are obviously caveats to this. Such as extending the light duration so long that it results in an unreasonable photoperiod (20 hours light, 4 hours dark)

Think of the total foot-candles per day that the plant requires, and then calculate how many hours you need your lights on to match that value.

For example:
If a plant requires 2000fc for 8 hours a day, then the target value is 16000fc-hours. (2000fc x 8 hours).

If your light setup provides a lower intensity, lets say 1500fc, then you will need to calculate the duration.
fc-hours = fc x hours
hours = fc-hours / fc
hours = 16000fc-hours / 1500fc
hours = 10.6 hours.

Obviously this applies mostly for extending the light duration to compensate for lower intensity.
If your lights provide higher intensity than the plant requires, then do not try to compensate by reducing the duration. I would suggest A.) Moving the light source further away from the plants, or B.) Getting lower intensity lights.

For example: If you had a 3000fc setup, and the plant only needs 1500fc for 8 hours.
Giving that plant 3000fc for 4 hours everyday will most likely kill the plant.

*Note: I do not know if the unit fc-hours actually exist, or if it is the correct unit name for this calculation. I just used that to represent the target daily light dosage.

Just to be clear: When a plant is commonly rated 500-1500 fc, does that mean 500-1500 fc for 4 hrs.? 8 hrs.? Longer?

Also:
I did a bunch of research on the web and decided to buy a light meter that has an accuracy level of 2%, can measure up to 10,000 foot candles (as if anything I'll measure will be that high), is made for this specific purpose, and comes highly recommended. It was fairly inexpensive, and it comes with a one-year guarantee, so if I'm dissatisfied, I can return it. It should arrive in a few days and I can't wait to try it out. Here is a link to the specs if anyone is interested.

Here is a link that might be useful: Light Meter

That was the first meter I had and got rid of it. It takes two hands to operate and it is too directional. It measures the source only in the direction it is pointed but does not give a good measure of the light on the leaf surface when the light is diffuse. And 4000 fc is really bright light for an orchid.

I've got the same Hydrofarm light meter terrestrial man recommended above. It's digital, and although it claims a top range of 5000 fc, it does fine up to full sun (8000 fc). I like that the large sensor averages the light value over its entire area. Also, because the sensor is separate from the meter, you can look at the meter while holding the sensor in any location or direction.

Here is a link that might be useful: Light meter

For what it's worth, I got one off eBay for about $20. I did not get it from this seller (see link below), but it's the identical model.

FYI: 1 foot-candle is about 10.77 lux. For most of us we can just take the lux output and divide by 10 to get a very good estimate of foot-candles.

L8r,
Don

Here is a link that might be useful: Light meter on eBay

Well, I got my meter today and it may indeed be a piece of junk--or it could be me. I don't mind the remote sensor as much as Richard does, but the meter seems to be VERY unspecific in the ranges I need it to read--unless I am missing something. From all I can gather, the meter has two levels, one for sun and HID (or just higher levels) and one for fluorescents, (or just lower levels). One takes up where the other leaves off. The fluorescent (lower) gauge is just calibrated to 10 X 100. I put it six inches beneath my bank of lights and the needle springs off the chart--but there is no way to read whether it is 1500 fc, 2000 fc, 2500 fc--just more than 1000 fc. If I flick the switch from fluorescent to sun/HID it reads 1000 x 6, or 6000 fc--an unbelievable reading for a bank of 4 T8s, right? They are on for 16 hrs a day and my phals would be dust by now at those levels, wouldn't they?

I wish I had been warned off this meter BEFORE I purchased it instead of after, but in all fairness several people had recommended Hydrofarm and I didn't go for it.

So which is more wrong here, me or the meter? The meter is supposed to be accurate with 2%. Is it even remotely possible my 4 T8s really are giving off 6000 fc of light? Or do I have grounds to return the meter and buy another one. What test can I use?

I notice in the highly recommended Hydrofarm meter you have a similar setup, two scales calibrated for low end and high end light. I suppose I could buy one of those at $25 or so and compare and still not be out a load of money...

I don't know what to do...

Maybe my meter is giving a perfectly good reading (hard to believe as it is), but how can I tell? And if I got the Hydrofarm and the readings differed, how would I know which one was correct? I guess I'm asking "What is truth?" or at least "Where can I find it?"

Frustrated Charlie

My meter is very much like Don's and also came from a seller on eBay. I have tested it against a borrowed VERY expensive meter and it was very close in it's readings. I have been very pleased with it. I think I paid around 30 for mine.
Pat...

Charley's Greenhouse was true to its word and gave me a full refund--and didn't ask me to return it if I believed it was defective, which I do.

Richard and Terrestial Man, I ordered the Hydrofarm as you advised. Hope I have better luck with it. At least if I have any questions about how to use it, I'll know who to ask :-).

Charlie

One of the best and cheapest light meters you can buy are the ones that used to be used in photography. I use an old GE meter, small and good enough for prime time.

Ask old relatives (over 50 or so) if they have one tucked away in a drawer somewhere that you can have. When the new cameras came out with built-in meters, people tended to keep the old meters even though they would never be used for photos again. Help them free up some storage space -- about the size of a cigarette pack.

You can also find these old ones on Ebay cheap. They work just fine for our orchid needs.

In camera light meters have to be accurate because film is very unforgiving of errors. That is why we need meters. I was not very impressed with my Hydrofarm meter but could not be bothered to return it. It simply up and died on its own about 8 months after buying it. I recently bought a kitchen scale for $15 at Target. They ran all the way up to $69 for the digital kinds. I was pretty surprised (but shouldn't have been) to find that I could tear off a 1/4lb chunk of ground beef pretty dead on target more than 90% of the time. A little perplexing is when two 1/4lb chunks as verified by my new scale didn't add up to 0.5lb! I guess a $15 scale isn't quite as precise as is neccessary for the pharmaceutical industry. There is a point in there somewhere but it can be summaraized thus: if in possession of a decent SLR with light meter you already have a better light meter than anything you can buy "cheap". You will have to learn the technique for using it, you don't simply point the camera at the plant and take a reading. Also, after a fairly short while you will 'see' light intensities and will kick yourself for dropping serious coin on a quality meter even while you might do the same thing for dropping $30 on a cheapo meter that doesn't work as well as you can.

H

Does anyone have any newer suggestions that would work with outside light levels as well? There are several apps, but I'd prefer a suggestion. Thank you.

This is a ten year old thread. In general once a thread has aged why not start a new one? That way you are the first to read and avoid all these 10 year old stories...

If you have a smart phone there are aps...