I bought a cheap lux meter off Amazon to get a better idea on how high to run my light since there are no manufacturer specs for our custom built lights. Here's a good quick read from the folks at Royal Queen.
HOW TO USE A LUX METER TO INCREASE YOUR CANNABIS YIELDS
For healthy growth and good yields, almost nothing is more important than providing your cannabis plants with plenty of light. With an affordable lux meter, you can measure and optimise the amount of light in your grow-op to increase your yields.
If you want to max-out your yields, you need to make sure that your cannabis plants are receiving
an adequate amount of light. With a lux meter, this all becomes easier than ever!
WHAT IS A LUX METER?
A lux meter is a relatively simple device with which you can measure the amount of light (lux=lumens/m²) in your grow room. What makes a lux meter attractive compared to a PAR meter or quantum light meters used by professionals is that it is much cheaper. While a good PAR meter can easily cost €1,000 or more, you can obtain a lux meter for a lot less. Simple lux meters start at €20 and upwards.
THE BENEFITS OF USING A LIGHT METER
Helps Increase Yield
A lux meter can help increase the yield of your cannabis plants—an obvious benefit to growers. With it, you can determine the optimal spots within your grow room, or you can use it to determine
the proper distance from your lights to your plants. A light meter/lux meter also lets you know when the light you’re using is simply not enough for maxing out yields.
Tells You When You Need To Replace HID Grow Lights
Some types of grow lights, such as MH/HPS bulbs, have a limited lifespan. In due time, they get increasingly dimmer, and this is why they need to be replaced at certain intervals. The light meter can reliably let you know when you need to replace your MH/HPS bulbs.
Prevents Some Plant Problems
Both insufficient light and too much light can be bad for your cannabis plants. The light meter can help you ensure healthy plant growth throughout all stages. The proper amount of light, not too much and not too little, will reduce stress on your plants, preventing further issues like
light burn and bleaching.
WHAT IS THE OPTIMAL AMOUNT OF LIGHT FOR CANNABIS PLANTS?
How much light your plants need will vary based on each phase of the grow cycle. Seedlings can’t take a lot of light, but once a plant is in veg, it needs just about all the light it can get. This allows plants to grow vigorously to their full potential. The same goes for flowering. Although plants in bloom thrive under a different spectrum of light than during veg, they still need a lot of light exposure to make sure the buds are as big as they can be.
HOW MUCH LIGHT DO YOUR CANNABIS PLANTS REQUIRE?
- Clones and seedlings: 5,000–7,000 lux
- Vegetative growth: 15,000–50,000 lux
- Flowering: 45,000–65,000 lux
- Maximum recommended amount of light: 75,000 lux
What about even more light? At some point, increasing the light beyond a threshold plant can manage will actually diminish returns. Said differently, once you reach about 85,000 lux, it’s simply too much. Some strains may already show signs of light stress at only 75,000 lux, with the risk of light bleaching increasing at over 80,000 lux. To keep it safe, it is best to stay at or below 75,000 lux.
HOW TO MEASURE HOW MUCH LIGHT YOUR PLANTS ARE GETTING
When you use a lux meter to measure the amount of light in your grow room, make sure you measure at the height of your plants’ canopy. This allows you to determine how much light they’re actually receiving. Even if the distribution of light across your growing area may appear even, you should take a number of measurements in different spots of the grow room. This is how you can find blind spots or optimal spots that are not always obvious to the unaided eye. When you locate these spots, you can rearrange your plants accordingly for best results.
A NOTE ABOUT LED LIGHTS
A lux meter works with all types of “white” lights, which includes HID, CFL, and white LEDs (COB LEDs). However, it doesn’t work with “purple” LED lights, which emit a purple light due to their combination of blue and red LEDs. Unfortunately, most cheaper LED lights are these purple types. So, if you use one of these for growing, you would have to rely on manufacturer information about how much light the product really emits. Alternatively, you could obtain a light meter that can be used with these types of LEDs. But be aware that these often cost a lot more.
.
).
and thanks for the pics of the build. Looking forward to seeing how the girls respond to them the next few weeks. You definitely upped your grow game 
.