Introduction

We like to garden inside as well as outside. And wouldn’t you know it, we don’t get much sun in the house. I built this grow light to use on a 4 plant hydroponic garden I built. My test subject for this light will be herbs.

Overview

The colors we are interested in for our light are red and blue. Different LED lights you can buy have differnet ratios of these two colors. There are excellent articles on the internet describing how plants use these two colors. Now if you want to view your plant’s natural beauty then this is not the light for you. For this light I used red and blue LEDs. I used 3 red LEDs for every Blue LED. Hopefully this provides some good results. If you want to view your plants then you’ll have to build a light using white LEDs.

Specifications

I built the light on perf board. See the pictures for the layout. The light draws 10.7 watts of power and runs on 12V. 1.5W is dissipated in the resisters. I used 136 LEDs and 34 100 ohm resisters.

Construction

Please use the pictures as a guide for construction. Each row contains a 100 ohm resister and four LEDs in series.

Greatly dimmed so you can see the LED colors.

Top view of Light.

Bottom view of light.

How Much Light Do You Need?

This is prob the biggest question. Depending on what you are growing you’ll need from 10W to 40W per square foot. Lettus and herbs will need 10W to 25W per square foot. And vegetables will need 25W to 40W per square foot. What you are aiming for is 50% to 70% of the watts per square foot used by an HPS light. For example if you use a 250W HID light you would need at least a 100W LED light.

What Can I Grow?

The ratio of red to blue is important to plant growth. This light has a high percentage of blue light. This makes it well suited for non flowing plants such as herbs.

Conclusion

This is an extremely bright light. It should provide enough light for a small garden. By small I mean less than 1 ft by 1 ft.