Don't use regular incandescent bulbs ("grow bulbs") or halogens to grow cannabis, this type of light generates huge internode spacing, poor vegetative growth, skimpy yields, and could set your grow room on fire due to the dangerous amounts of heat these lights produce.
Spend your money wisely, invest in
- Fluorescent lighting (good), or
- High Intensity Discharge lamps (HID-- recommended). HID lighting such as
- Metal Halide (MH) (see #mh or #cmh) or
- High-Pressure Sodium (HPS) supply the high-intensity light that cannabis needs for good growth and large buds. (see #hps)
- LED lamps have improved in past years to the level that they can replace HID lamps (especially new chips) - but they still have higher purchase costs than HID. (see #led)
Added technical information why halogen lighting is a poor choice for plant cultivation by wannabee2004:
Q: Do halogen bulbs have a good spectral output for plant growth?
A: No, the spectral plot output of various halogen bulb types is by far the worst.
Q: Are they efficient at generating useful light for plant growth?
A: No, the best floro/hps/mh lighting each being approx 5X more efficient at plant growth than halogen.
A good way to measure plant growth efficiency of different types of lighting is PAReff. PAR stands for Photosynthetic Active Radiation: the wavelength range of light between 400 and 700 nm that can be absorbed by leafs for plant photosynthesis. PAReff is the PAR/Watt efficiency ratio over a certain area.
Some examples:
Philips Advantage Fluorescent, 5000K: 1.44 PAReff
Philips High Pressure Sodium deluxe: 1.38 PAReff
Philips Dense-Line Emitter Metal Halide, 4100K: 1.38 PAReff
Philips Spot Halogen Masterline, 2950K: 0.263 PAReff
People usually choose halogen for the “low startup” costs of a halogen light. The real costs of halogens result from its low efficiency. 500 Watt halogen lighting produces about 0.08 Watt/s/nm in the green-yellow spectral region which is about the same as 80 watts of cfl’s. A 500w halogen grow will cost approx $63 for electricity, whereas a more efficient light source generates the same par value for around $10 (depending on your local prices).