Yeah, That is the wrong lamp. You should never buy one of those "Plant" lights sold at most stores, particularly if they are incandescent. Incandescent lamps can waste as much a 90% power the electricity consumed as heat, not light. Also, The color of the lamp is too wide spectrum and much of the light emitted is orange, yellow & green which is not used by plants. Even if the light you see from it looks whitish, this is what it consist of. Even a cool white fluorescent has a better output then one of these for growing plants. Oh well, most of us make that mistake. . . Also, as far as the light fixture is concerned, The lamp you have is loosing too much light through the shade so only about 30% or 40% of the light from the bulb is going to your plants and the half globe is also absorbing/blocking much of the usable spectrum from any type of lamp you would put in there. The wattage ratings for light fixtures are based on the amount of heat emitted from the lamp that is out in, not the amount of electricity flowing through it. You should have been able to find one rated to 60 watts, 40 is pretty low. The advantage of fluorescent lamps is that the light output to power consumed is about three times that of incandescent, maybe a little bit less with CFLs rather that tubes. So a single 40 watt lamp gives off approximately the equivalent of 120 watts of incandescent or three times the light from the bulb you've bought. The CFL in the picture below is 43 watts or 47 watts or somewhere around that.

Thought I would update my "Growing under lights" experiment. Here are two of the same plant. The one on the left has been under lights since early October, while the other one has been in an east facing window for about the same time. Notice not only the color difference but the leaves on the left plant are growing out not down (somewhat hard to appreciate) as is seen on the right plant.... I guess lights work!!!!! I started with a 12 hour "day" and have been decreasing to about 10 hours.

the flourecent bulbs mike is talking about run on very low energy and dont heat up, you wont have to worry about fires at all. if you go with the high presure sodium then ur runnin a high watt high heat bulb and you need to worry. (also u may need to notify your insurance company its in the house.) incadacent bulbs are the same there high heat and higher risk of fires. if it were me i wouldnt split the light. just put it on a timer and let it run at whatever length of time u decide. i leave mine all day (around 16 hours) and they get maybe 5 hours of sun through the east facing window there in. the other thing thats good about flourecent and its low heat out put is it can be placed inches from your plants without having to worry about burning the leaves and this insures the most effective use of all the light given off. mine hang a few feet above as i have alot of trees to cover but it works great. my mandarine tree even has flowers and fruit and all my other trees are experienceing great new growth right now hope that helps abit chris

Suggest that you look for corrosion on the connector nearest your headlight, and/or any connector in the same circuit that is exposed to dirt/water/spray. This type of corrosion will result in a voltage drop across the connector, perhaps 3 or 4 volts. In this case, your headlight doesn't see 12 volts, it sees 12-4 = 8 volts, and it will be noticeably dim. When you find the bad connector, you can shine up the metal parts with steel wool, and then coat them with electrical grease to prevent the entry of water. If the connector is located where repeated exposure to road spray is likely, you can wrap it with electrical tape, as well. All of the above can be completed in two hours, for less than 20 dollars.