We are now halfway through our HID vs. LED grow light comparison

In part 1 of our series comparing the performance of the RhinoGrow 400 LED grow light (172 watts) to a 400-watt high pressure sodium (HPS) lamp, we described the growing space and the starved state of the test plants.

The exact cause of the damage is unknown, but I’m sure it has to do with the solution used by the supplier of the clones. With the first watering, the grower observed that the excess water was cloudy-white. The clones were thoroughly flushed with clean water before planting in their containers of soil.

I’m happy to report that both plants recovered very nicely. The plants reached the grower’s target height after 12 days of vegetative growth instead of 7 days. This is an average recovery time for damaged plants, and should not affect the test.

When flowering was induced, the plants (Sensi Seeds Fruity Juice) were 12″ – 13″ (HPS) and 10″ – 11″ (LED) tall. The HPS plant was taller and had slightly larger leaves by this point, with a lot more bare stem (more space between leaves) than the LED plant, which was growing outward more than upward.

Flowers were beginning to show 8 days after switching to the flowering cycle

After 8 days in the flowering cycle, the HPS plant was 4″ taller than the LED plant, and still had larger leaves and more bare stem. The plants were about 18″ (HPS) and 14″ (LED) tall at this point. At this stage, I thought that the RhinoGrow was losing the battle, but that didn’t last long.

By day 16 of the flowering cycle buds are quite nice to look at and trichomes can be seen on leaves.

After 16 days of flowering, the plants were about 22″ (HPS) and 18″ (LED) tall. By now, both plants were slowing their vertical growth to a halt and producing buds. Even though the LED plant has been consistently shorter, it was clear by this point that both plants were going to produce a similar number of buds. The HPS plant was mainly building more stem.

The fact that the leaves of the HPS plant have consistently been slightly larger than those of the LED plant is very significant. Since leaves are the energy source of the plants (like solar panels), the larger leaf surface allows more energy to be produced. If the HPS produces a heavier harvest, this may be the reason.

The test plants are now 26 days into the flowering cycle, which is about halfway through.

After 26 days of flowering, both plants look beautiful. They still have approximately 4 weeks left before harvest, and a lot more growing to do. As you can see, there is really not much difference in bud size or quantity, the difference is mainly in plant height.

HPS (400w) test plant after 26 days of flowering.

RhinoGrow 400 (172 watt LED) test plant after 26 days of flowering.