Newbie question regarding 8w LED bulbs...

[el_bevrus]

Hey,

I haven't studied electronics since high school 15 years ago, which wasn horribly taught at my school and killed any interest I might have developed in the subject. Fast forward 15 years and i'm a furniture making student getting really interested all of a sudden in the maker movement and the overlap between technology (electronics specifically) and craft. I've just bought myself a Make Magazine guide to electronics for beginners, a book on Arduino for beginners, and various bits and bobs and tools which has cost me a small fortune. The Make book has arrived but unfortunately i'm waiting on the electonic components and tools I need to follow the exercises to arrive in the post. So as it stands my knowledge of electronics can currently be considered ZERO I'm desparate to start gaining knowledge for my first electonics/carpentry crossover project and was wondering if anyone here could help?

I have a project in mind where I would like to power a readily available LED bulb (I'm thinking the 8w Ikea LEDARE: http://www.ikea.com/us/en/catalog/products/70254098/ ) for the purpose of a reading lamp? Would it be possible to power this bulb using batteries alone? I'm trying to make it child safe and don't want the kid to be able to put their finger in a mains powered light fitting. I thought batteries would make things safer with the additional benefit of being portable. Again, I am a COMPLETE beginner at electronics so apologies if this is a kind of silly question.

Thanks for your help in advance!

 

[el_bevrus]

A friend has already pointed out that the LED bulbs designed for light fittings probably have some sort of 240v > 12v(?) transformer built in and therefor it wouldn't be possible to power the Ikea bulb with batteries. I'd like to achieve the same quality of light (the equivilent of a 40w filament bulb, with a kelvin value of around 2700 kelvin) manually with LEDs and batteries. How would I go about doing this? Any thoughts on how to diffuse the light a little for a softer effect?

 

[Arouse1973]

Never taken one apart but I would have thought it would have a capacitor in line to reduce the current to the LEDs. So technically yes this could be done with some modification like remove the capacitor and maybe change the resistor values in they have any. Can you take one a part and show us some pictures.
One word of warning though. It is a bad idea to convert anything that can be plugged into the mains and which now runs from a lower voltage d.c because someone could plug this in to the mains and BANG!!. This is the reason why you should only use say the IEC kettle leads for mains only. Even though they look like they would make a nice sturdy low voltage d.c connector.
You have been warned.
Adam

 

[BobK]

You can buy the LEDs without the electronics for less money. Look for 3W LEDs on Ebay for instance. One of these might be enough. Two would probably produce more light than the IKEA one you linked, since it is not particularly efficient. Then you want a constant current driver for them.

Here is an example of warm white LEDs:

http://www.ebay.com/itm/10PCS-3W-Wa...547?pt=LH_DefaultDomain_0&hash=item1e7e4436b3

Bob

 

[el_bevrus]

Thanks both for the reply. It's a good point about converting a normal looking bulb into a lower voltage d.c and the associated dangers of this.

I didn't realise the commercial LED light fittings were less efficient. I think a friend may have a 3w LED i can test out to check the amount of brightness produced. Like you say, one may be enough. Originally I wanted to offer the user of the item I am designing the ability to replace dead bulbs easily (as it's for children it's probably going to have to endure a lot of rough and tumble) but a homemade LED circuit might be durable enough that it won't need replaced. I've seen people encase LEDs in silicon to diffuse the light - maybe this'll offer enough protection?

 

[BobK]

State of the art is better than 100 lumens / watt. The bulb you pointed to is 50 lumens per watt.

Bob

 

[el_bevrus]

I've been looking around on ebay for 3w LEDs - I noticed that the lower powered 1w LEDs are more efficient than their 3w counterparts (more lumens per watt). If I wanted to create a light source as close to that Ikea bulb as possible (say around 400 lumens in a warm white) would I be better using 3 x 1w LEDs or 1 x 3w LED? Heat is my primary concern as i'd like to cast the LEDs into silicon.

 

[BobK]

Well, the 3 1W LEDs would produce a little less heat since they are more efficient, and it would be distruted over a larger area, which would require less heat sinking to keep it at the same temp as the 3W. So 3 x 1W is the winner. Unless space is a problem.

Bob