Can I grow with 150 watts HPS light in a 3 x 4 room? The answer is both Yes and NO. No means, you may have that light if you want but you will not get the desired result at the end of the day for high light requiring plants. The answer is yes if the plants are not demanding too much light and the actual grow space does not take up the entire room. Say, if the plants grow only in the 2 sq ft area, the 150 watts light is enough.
The watts and the light intensity are related to the total coverage area of the grow light. The coverage area of the light means how much the light can cover in a given space. The coverage area is applicable to the area in which the plants actually grow and not the entire grow space. You may use the 150 watt HPS grow light if you are growing smaller plants, provided the grow light system has effective cooling system with it.
How to relate the grow light wattage and coverage area?
It is a fact that the coverage area increases with the grow light wattage. Low watts grow lights are used for smaller grow areas. The coverage area is the total area of a given grow space. The plants need a particular wattage of light per square area. The calculation is done by multiplying the needed watts per square foot with the total area. Example for high light plants is tomato plant that demands 40 watts per sq area. For the tomato growing in a 2 x 2 grow space, the calculation is done as
- 2 x 2 = 4 sq ft
- 4 x 40 watts = 160 watts
So a 150 watt HPS light would be just enough for a 4 sq ft grow area. With effective cooling system that allows closer placement of the light and a reflector can increase the light intensity to match the calculated wattage of light. It is not necessary that a 3 x 4 room will have that much plant growing. If the growing is done in a 3 x 3 sq ft area, the 150 watts light is not enough and you may want to look for a better option.
Grow light height and coverage area
The height at which the grow light is fixed also plays a role in its effectiveness. The coverage area is increased with height. But in certain cases, the light intensity is reduced and this is where the reflectors come into play. It redirects the light rays that would have gone up towards the growing plants and no light is wasted. The ideal height for a 150 watts HPS light would be 6-8 inches above the top of the plants growing.
The bottom line is that the 150 watts HPS light is more suitable for small herbs like lettuce, basil etc. For vegetables like tomatoes, it is better to go for a higher wattage HPS light for best results.