DIY LED reading light

kingkong · Post by **kingkong** » Tue Nov 21, 2006 12:14 pm

hi,

anyone has a LED reading light plan (components list, circuit diagram, physical plan, etc.) to share? looking for ideas to buid one.

i'll share mine here when it's done.

thanks.

--kong

Post by **weixing** » Tue Nov 21, 2006 12:56 pm

Hi,
Err... what do you mean by "LED reading light plan"??

A simple LED light can be made by connecting to a LED(s) to a current limiting resistor in series and a DC power source.

Have a nice day.

kingkong · Post by **kingkong** » Tue Nov 21, 2006 1:20 pm

thanks weixing, for your reply.

yes. a number of LED's in parallel in series with a pot to adjust the brighness is what i've in mind currently, but....

should i stick with a fix resistor?
how bright is too bright?
how many LED's?
how do you mount the LED's?
what about batteries?
how long will batteries last?
is it better to use main+adapter - since it's for use in the obs?
etc. etc. ergonomics and practical issues.

Canopus Lim · Post by **Canopus Lim** » Tue Nov 21, 2006 2:20 pm

If you make it adjustable by controlling the current to the LED (and hence it controls the brightness of the LED), you will not face the problem of being too bright or too dim. However, it may be more practical to buy a proper LED flashlight as it comes with the casing, better soldered components with PCB board and it is more compact than making one. Reliability is also a problem when DIYing.

Post by **weixing** » Tue Nov 21, 2006 2:28 pm

Hi,

yes. a number of LED's in parallel in series with a pot to adjust the brighness is what i've in mind currently, but....

Don't put LEDs in parallel directly as this'll cause the brightness of the LEDs not been equal. If you want put LEDs in parallel, you need to have a limiting current resistor on each branch.

should i stick with a fix resistor?

Easier to do but you'll not be able to control the brightness.

how bright is too bright?

You need to experiment with it. Hmm... a circuit with brightness that can be adjust will be more useful in this case.

how many LED's?

That's depend on how large the area that you want to illuminate and the type of LED you have... low power, standard or high power LEDs. You can use a single high power one if the illuminate area is not big or a few if you have only low power LEDs. Remember, you need a higher supply voltage if more LEDs are use.

how do you mount the LED's?

That also depend on you... you don't want to look nice than just mount on the circuit board directly or can use a LED holder to hold it.

what about batteries?

That's also depend on you. What type of battery do you have?? Do you need to lighting to be portable or is on a fix area. If you need to be portable, AA/AAA/C/D size rechargeable batter can be use. If the lighting is to be fix on a place, a Seal Lead Acid Battery or a power adapter can be used.

how long will batteries last?

This depend on the how much current the circuit use. If your circuit use 500mA (0.5A) and you use a 7AH battery, your 7AH battery will last around 14hours (7/0.5).

is it better to use main+adapter - since it's for use in the obs?

If it in a observatory, of couse a power adapter will be better.

Have a nice day.

kong · Post by **kong** » Tue Nov 21, 2006 4:37 pm

Canopus Lim wrote:If you make it adjustable by controlling the current to the LED (and hence it controls the brightness of the LED), you will not face the problem of being too bright or too dim. However, it may be more practical to buy a proper LED flashlight as it comes with the casing, better soldered components with PCB board and it is more compact than making one. Reliability is also a problem when DIYing.

yeah. but if i build my own, i can have one that fit my requirements exactly. i just need to experiment with different setup. the LED cct is of course pretty simple to build - compared to a dew heater controller and the 3/5/9/12v power supply - if i'm to build that for the LED light...
and i havent seen a commercial one with brightness adjustment...

river · Post by **river** » Tue Nov 21, 2006 5:27 pm

any reason you want to use LED? is it Zero flickering or other reason?

Are you considering Red light or white light?

why not put a table lamp with brightness control in the Ob? Then Stick on a red filter if you like.

kingkong · Post by **kingkong** » Tue Nov 21, 2006 6:13 pm

river wrote:why not put a table lamp with brightness control in the Ob? Then Stick on a red filter if you like.

i think the smallest table lamp is still way too bright. i used a bicycle-type red LED backlight during a trip to mersing 3 months back and almost ended up being tied to a coconut tree by some fellow amateur astronomers...

Clifford60 · Post by **Clifford60** » Tue Nov 21, 2006 10:34 pm

If you use simple DC (battery) to power the LED, the battery will not last very long, like WX mentioned 14 hrs if the batt is 7Ah. So why LED flash light last so long (a single AAA 650mAh batt is good enough), they convert the DC to PWM circuit to power the LED, based on the duty cycle, you can control the brightness and how long the batt going to last. Also, the brightness depends on the grade of the LED. I saw a single 3W white LED at SL Sq, it blind me at 2m away.

cataclysm · Post by **cataclysm** » Tue Nov 21, 2006 11:18 pm

Hi I had my homemade LED torch that survived field test on last Mersing trip. Its really a simple device that runs off 2 AAA batteries on a single red LED( larger than 'normal') bulb. To keep the circuitry as simple as possible, I relied on a pair of fixed resistors soldered // in the circuit. Can't quite recalled the resistors rating, they are spares from my other projects. Its more a mix and match to obtain the brightness I required.