Read this post for some helpful tips in understanding lumens and lux and learn how to get an estimate of what kind of lux your plants are being exposed to.
Candela: This is the equivalent of horsepower for lights. 1 Candela = the amount of light given off of a candle. You'll rarely see a bulb lists it's candela, but it's necessary to calculate lumens
Lumens: This is the calculation of the amount of light a light bulb gives off generally. Usually the manufacturer of a bulb will tell you the lumens coming off of it, but it's the spherical measure of the amount of candelas coming out of a bulb at a given radius.
Lux: Once you know your lumens, you can calculate lux. Lux is the amount of actual light that is falling on a given area. A good way to think about it is a flashlight. Imagine you have a flashlight with an adjustable lens and you are shining it at a wall in a dark room. If you tilt the lens so that it is wide angled, you will illuminate more of the wall, but the light will be less bright. If you focus the lens, you'll illuminate just a spot on the wall, but it will be very bright. In either case, the lumens of light you are shining at the wall is the same, as the flashlight isn't producing more or less light, what has changed is the lux. Lux is the amount of lumens hitting a given area. The smaller the area, the greater the lux. Now imagine that you have your flashlight focused in so that it's a tight beam, and then you take a step back from the wall. You are illuminating more of the wall now, but that illuminated area is less bright. The distance from the light source to the light destination is key in calculating your lux.
Applied to hydroponics:
Having a good feel for lumens and lux is key in hydroponics as it will help you position your grow lights to maximize your lumens over a given area (aka lux). If you get a high wattage light (say 1000 watts), how far should you put it away from your plants? We're going to go into more detail on how you can overdose lux for your plants in the next blog post, but for now here's a good way to use what the bulb manufacturer is telling you about your lights to calculate your lux and therefore the distance you should place your bulbs.
What you should know:
- The wattage of your bulb
- The type of bulb you are using
- The size of the area you are shining the light onto
- The distance you want to shine your lights from
Next, go to this handy calculator website and enter the above information. It will spit out the general Lux number you will be receiving. What this does not do though, is deal with distance. The rule of thumb is that your lux will decrease by the square of the distance from the source. See the following example:
Take that distance number and square it. So 2 feet become 4 feet. 3^2 becomes 9, etc. Now divide your lux number by that squared distance. In my example of my bulb being 3 feet away from my plants, we would get a lux of 6243/9 = ~693 lx per sq ft.
And that's how you estimate your lux, based upon the manufacturing information. Now manufacturers are not always 100% accurate, and bulbs to change overtime, so a live, lux-calculating sensor will be a big help, right? We're going to be building a more sophisticated calculator in the next week or so and will post it soon, so you can keep estimating and getting ready for your live readings. Until then!