Someone on a social site asked if anyone knew of a light meter that would measure the amount of light in their garden. I burst out in laughter thinking this was a great joke. Then someone posted a link to just such a product; the Sunlight Calculator. I cried. Are people really buying such a product?
Sunlight Calculator – The Claims
The following are taken from the dealers ad.
- “The lighting conditions of the micro-climates in your garden aren’t always obvious.” Yes they are – just hold out your hand and look for shadows.
- “This meter measures the duration and intensity of sunlight falling at a given spot over a 12-hour period.” It might measure these things but it does not report them. It only reports sun, part sun, part shade or shade. You get neither duration nor intensity readings.
- “Though not a panacea for all garden problems, it can help you locate plants where they will grow best.” Not really, since light levels are just one of the parameters to consider.
SunCalc® – How It Works
After you turn it on, the meter measure the amount of light for 12 hours and determines how much sun you have. That is simple enough.
What happens if you turn it on at noon?
Sunlight Calculator then measure light for only part of the day, and will give you the wrong readings. So to make this work you need to go outside and turn it on before sunup. Sorry – I am in bed sleeping.
The Sunlight Calculator gives one of four readings which translate into the following.
- Full sun: 6+ hours
- Partial sun: 4-6 hours
- Partial shade: 1.5 – 4 hours
- Full shade: less then 1.5 hours
May I suggest that if you go outside 3 or 4 times during a single day, and look up, you can determine these values without a meter. Warning – do not look directly at the sun.
If you are a visual learner, my video will show you how to make a sun map.
If the above video does not play, use this link: https://youtu.be/AAIhO_olcDg
Is SunCalc Faster Than Pen and Paper?
Added Aug 2023.
This blog post has received more negative feedback than almost every other one I have written. Several people claim that they don’t have time to go outside and use the paper method and the CunCalc is so much more efficient and faster. I decided to put that claim to the test. I compared SunCalc and my paper method for a fairly small garden consisting of 2 beds with a total of 274 square feet.
Pen and Paper: Total time was 60 minutes spread over 1 day.
SunCalc: Total time was 121 minutes spread over 67 days.
You can see the full details of this experiment in this video.
Plants Require Sun or Shade
Some plants prefer sun and some prefer shade. Almost all will grow in part sun/shade. The more I grow things the more I am surprised that so called sun plants do just fine in shade and vice versa. The plants are adaptable.
My shade garden was shaded by two medium sized sugar maples. The two trees had to be removed one winter, and my garden was suddenly a full sun garden. All of the plants did just fine. Some of the shade plants are actually growing better now than before. Admittedly, this garden does get watered a couple of times a season, but it can go several weeks without water.
Accuracy of Plant Information
Some people claim that just knowing sun or shade is not accurate enough and that plants are fussier than that. They might be fussier but plant labels and on line information about plants is not more detailed. Look at plant labels and check the light requirements. They are not more detailed than sun, shade or part shade, and most give a range, “sun to part shade”.
Keep in mind that the same plant label is used over a wide geographic area. We get the same plant label here in Ontario that is used in California, but full sun in the two areas means something completely different. We grow hydrangea in full sun in Ontario, while the south recommends part shade.
Two-thirds of the technical brochure deals with something called “isolation level”. There are lots of formulas and technical information on this, but it never tells you how you should use the information.
Here is some of it. WARNING: read this only if you want a nap.
The values are generally expressed in kWh/m²/day. This is the amount of solar energy that strikes a square meter of the earth’s surface in a single day. Of course, this value is averaged to account for differences in day length. There are several units used throughout the world.
The conversions based on surface area are: 1 kWh/m²/day = 317.1 btu/ft²/day = 3.6MJ/m²/day
The raw energy conversions are:1kWh = 3412 Btu = 3.6MJ = 859.8kcal
Do they really believe gardeners are going to do these calculations?
Stop Buying Unnecessary Products
The Sunlight Calculator is not something you need. You can make a sun map following the procedure in my video in less than an hour and you don’t have to buy anything.
What really bothers me about such products is that they are damaging the environment. The product needs to be manufactured, packaged, and shipped around the country – probably half way around the world. That all takes resources including oil. In the process it adds pollution to the environment and increases global warming. You will use it once, and store it in the shed.
If you care about the environment – don’t buy the Sunlight Calculator.