Hardiness may be the first number that Canadian gardeners look for when considering a plant, but right next in line is its sun requirement. So, when a simple instrument became available to measure sunlight levels in a garden, I quickly bought one. Unfortunately, its practical deficiencies soon became apparent.
Basically, the unit is dumbed down to such an extent that it only gives four readings, labelled full and partial sun, partial and full shade. No definitions of these terms are supplied with the unit, but they are provided on the company's website. Full sun is 6 hours a day. Not only that, but the unit gives no reading whatsoever until precisely 12 hours has passed, no less, no more. That may be suitable for the mid to south USA, but here in Canada our summer days are 16 hours or more. 6 hours is less than half sun here, not full. And, the company refuses to provide details on how the unit defines 'sun' and 'not sun'.
Accurate measurements confirm these weaknesses - the unit displays "full sun" in as low as 45% sun on a clear day. The cloudier the day, the more variable the SunCalc's response is.
Obviously, the unit needs a numeric display, hours sunlight accumulated, displayed while the unit is operating. The unit needs to keep accumulating sunlight until turned off if it's to be adequate for northern gardens. And, the gardener needs to trust how the unit decides it is in sun.
So, as I said, brilliant idea. But given its design flaws, it's a waste of money until its design is improved.