AC and DC power to light a Bulb

I understand the solar cell is not powerful enough to light a 60 watt bulb.  I also understand that I can use LED's to achieve a lower energy light source.  BUT, the goal of my experiment is to stand outside with a solar cell in the sunlight, feed the 10v 500ma DC power to the 60 watt bulb, and then have the wall plug supplement the rest of the electricity, apparently it will take 55 watts of AC power.  I'm not sure if a lightbulb would just take 60 watts and perhaps be about 5vdc brighter, or if the bulb would be smart enought to just take the 55 watts to reach it's intended peak.  But this is what I'm trying to do, supplement a bulb plugged into a AC grid with DC power.

A regular incandescent lightbulb isn't really "smart."  It is a small length of wire in a glass bulb that heats up and emits light when current is passed through it.

A simple analogy is to equate the lightbulb to a resistor.  It's slightly different from a normal resistor because it is non-linear, but for our purposes, we can call it a resistor.

When the manufaturer says that the lightbulb is 60W, it DOESN'T mean that when we connect it to a power supply it will always draw 60W, and it DOESN'T mean that we need to give it 60W of power for it to produce light.

When the manufaturer says that the lightbulb is 60W, it DOES mean that when we connect it to the mains where the bulb was designed to be used, it will draw about 60W of power from mains.

If we think of the lightbulb as a resistor and this lightbulb was designed for a mains supply of 120Vrms and the lightbulb is rated at 60W, we can calculate the resistance of the lightbulb.  The formula P = V^2/R solved for R with 120 as V and 60 as P will give us R = 240 Ohms.

A lightbulb is simply a "dumb" wire or resistor that will pass both Alternating and Direct Current.  If we took our 240Ohm (60W @ 120V) lightbulb and connected it to the 10Vdc solar panel, the lightbulb would draw P = V^2/R = 10^2/240 = 0.416W.  That power draw will heat up the wire in the lightbulb and it will produce light.  The light may be imperceptible.

What it sounds like you want to do is to utlize all of the power that the solar panel can produce to provide power to the lightbulb in addition to providing AC power from the mains to provide a total of 60W of power to a lightbulb.  We already found out that the lightbulb won't draw the full power of the solar panel with a "dumb" circuit.  The short answer to doing what you want to do is that you will need some power management electronics to boost the DC voltage from the solar panel and reduce the voltage from the mains to provide a total power of 60W to the lightbulb.  The incandescent lightbulb will light with a current that has a DC average and a much larger AC component added to it, but to control the power sent to the lightbulb in the way you want is a lot more complex.

CFL and LED lamps that are meant to plug into the mains are much more complex than an incadescent lamp.  Most CFLs are so sensitive to the voltage and frequency of their power supply that they won't work with dimmer switches; trying to add a DC component to the mains could be bad.

donny662 thanks for all your well explained knowledge!  Thats exactly the answer I was looking for...  You've check my "you learn something new everyday" box, thank you.

From your information here I gather that adding the DC power to that provided from the grid would just make the bulb a bit brighter, and that's not what I'm trying to do (save a bit of energy).  To accomplish what I'm trying to I guess I'd need a virtural AC dimmer switch when DC power is being provided.

I guess I could bypass my AC current issue by using a DC converter, but I don't think they are very energy efficient as they are normally warm to the touch when unplugged from the wall...that's got to be a waste.

On a side note, why do traditional table or floor lamps come with a note that says "60 watt max" or "40 watt max" if its all up to the bulb basically playing the part of a resistor on the grid...  It always seemed to me that bulbs higher than the rated wattage will fail much faster if put in to a lower rated socket.  Just a thought...

donny662 thanks for all your well explained knowledge!  Thats exactly the answer I was looking for...  You've check my "you learn something new everyday" box, thank you.

From your information here I gather that adding the DC power to that provided from the grid would just make the bulb a bit brighter, and that's not what I'm trying to do (save a bit of energy).  To accomplish what I'm trying to I guess I'd need a virtural AC dimmer switch when DC power is being provided.

I guess I could bypass my AC current issue by using a DC converter, but I don't think they are very energy efficient as they are normally warm to the touch when unplugged from the wall...that's got to be a waste.

On a side note, why do traditional table or floor lamps come with a note that says "60 watt max" or "40 watt max" if its all up to the bulb basically playing the part of a resistor on the grid...  It always seemed to me that bulbs higher than the rated wattage will fail much faster if put in to a lower rated socket.  Just a thought...

Remember that an incandescent bulb is not very efficient at producing light.  A 60W bulb draws 60W from the grid; a few of those watts of electrical power are converted into light power, but the rest of the electrical power is converted into heat energy.

When a floor lamp says "60W max," it is saying that because the fixture can only handle the heat from a 60W incandescent bulb or lower.  Higher wattage bulbs produce more heat, which can be a fire hazard or otherwise damage the fixture and reduce the life of the bulb.  Fixtures rated for higher wattage bulbs are made from materials that can handle the heat and/or have enough ventilation to get rid of the extra heat.

Also, you'll probably notice that CFLs will not last as long in fixtures that are poorly ventilated and rated for lower wattage incandescents. The heat from a 26W CFL may not be enough to damage the fixture, but the poor ventilation will let the CFL get hot enough to reduce its lifetime.