The reason I would rather use 300w bulbs is that neither bulb is available in Iceland, so I have to order from the US. At most sources I have seen, the ESD 150W bulbs are 20-35 dollars, the ELH 300w bulbs are 10-12 dollars. The ESD are rated for 12 hours average life, and the ELH bulbs are rated for 35 hours. So using the 300w bulbs saves me a lot of money -- I also have to pay 25% tax on the cost of the bulbs, as well as on the shipping, so it really adds up.