So I got a par meter to measure my lights. I put the sensor into my tank and my meter shows zero. In my tank I have the Fluval marine 3 but I am planning to replace them with two ai prime 16 hds. When I put the sensor under the prime lights the meter reads 8 and about 12 in. Only when I have the meter really close to the light does it read higher than 200. What am I doing wrong with this meter?