LED Brightness

What makes some LEDs brighter - and more durable - than the others?

The Maglite Solitaire has a tiny LED that uses a 1.5V AAA cell to produce 47 lumens. On the other hand, the standard bulb distributed by electric utility companies like UPs PVVNL uses 7W from the grid to produce 700 lumens of light.

In terms of lumens per watt (lm/W), the stardard measure of lighting efficiency, the Maglite stands at 33.5 lm/W and the UP bulb at 100 lm/W. Both are small change compared to recent innovations from companies like Philips which have produced lighting units that can produce more than 200 lm/W!

However, as anybody who has used a Chinese LED bulb/panel would attest, it takes a lot more than just lighting efficiency to measure durability and useful life of an LED bulb.

Considering the fact that the super efficient LEDs from companies like Nichia-Japan and Philips are beyond the reach of regular users, is there any global standard that sets the benchmark for LEDs that strike the best balance between lighting efficacy and affordability?


-----------------------------------------------------------
LINKS

- Top 10 LED manufacturers - http://www.ledsmagazine.com/articles/2011/02/strategies-unlimited-unveils-top-ten-list-of-led-manufacturers.html
- Maglite - http://maglite.com/shop/maglite-solitaire-led-1-cell-aaa-flashlight.html#.WCoFWNV97IU
- Philips - now more than 200 lm/w - http://www.philips.com/consumerfiles/newscenter/main/design/resources/pdf/Inside-Innovation-Backgrounder-Lumens-per-Watt.pdf
- Super high luminous efficacy - http://phys.org/news/2010-08-white-super-high-luminous-efficacy.html
- Energy storage in batteries - http://www.allaboutbatteries.com/Energy-tables.html

Solar Lighting a Dark Stairwell

How much does it take to set up a solar-powered system?

I've been mulling over the installation of a solar-based back-up for a while now. For starters, I wanted to install a self-contained system that automatically lights up our building stairwell. 

The problem is quite straightforward: We stay in an apartment complex that has about 30 towers (4x4 houses each), without a central power back-up. Each apartment has a stairwell that is vulnerable to power outages. At night - especially in winters - it becomes particularly difficult for the children and the elderly to use the staircases.

From whatever little I have gathered so far from the net, a solar-panel based lighting system would require: solar panels, a charge Controller, a deep discharge battery, wiring (4mm), a light-activated switch, and a panel of LED lights.

What I do not know for sure - and this is an ongoing challenge -  are questions for which I am yet to find dependable advise:

• How do I align the panels on the terrace so that they can be installed - and maintained -  easily?
• The most appropriate configuration of panel + controller + battery + LED panels?
• Which is a reliable place from where I can buy the components?

At least in NCR Delhi, it is difficult to find somebody who can guide you. The shopkeepers and aggregators always want to sell you the biggest system possible, whether you need it or not. They are all chasing contracts from big-ticket clients - the railways, public-sector companies, large housing complexes to keep the assembly lines running. Companies like Simpa Networks are building models that resemble telecom service providers. Not for them the one-time pocket-change from individual residences.

Reliability is also an issue. Almost none of the components comes with a performance guarantee. The usual refrain is "electronic cheez hai, kuch bhi ho sakta hai..." (its electronic stuff - anything can go wrong!). Not an encouraging start for people who see this as a long-term investment in clean energy.

Amongst all the people I have met, the most sensible advise came from a marketing executive at Maharshi Vedic Construction. His point was simple - longevity of any equipment depends on how you go about maintaining it. He gave the example of an inverter he has installed at home 17 years ago. According to him, regular vacuum cleaning and greasing is all it takes to make electrical equipment last longer. Clearly he had a point.

Yet, even as a manufacturer of solar panels and controllers, he could not offer a formal performance guarantee for the stuff he was selling. His panels cost INR40/Wa, so a 60Wa panel cost INR2400. The controllers were available only for 10A and 20A with a starting price of INR1100 (note: the 10A model came with a useful USB charging port).

Ultimately, I ended up buying the following stuff from the electonics wholesale market at Bhagirathi Palace, Old Delhi:

- Solar Panel Tata BP - 60Wa (INR 1200)

- Charge Controller - (INR 250)

- LED lights set - 12W (INR 150)

- Twilight Switch - 12V, 6A (INR 368) - from Electrocine Corp, 1801/5-6, Bhagirath Palace

- Copper wire (INR 160 for 10m - Kalinga Gold 4mm copper wire) 

- Battery - 26Ah, 12V

I was about to purchase a new 28Ah battery when a friend offered to pass on an old battery he was going to dump anyway. It has been purchased a year ago but seemed to have got completely discharged due to non-use. It took three about three days for the voltage to climb over 12V.

Apart from the battery glitch, the system seems to be working beautifully. 

Now, only a few questions remain: The battery runs out of juice in just four hours...is the LED panel drawing out more power than 12W? Or is it just an old, deep-discharged SMF battery acting up? How does one measure the W/h remaining in a battery unit?

-----------------------------------------------------------

Vendor's Contacts:

* DC Twilight Switch - Electrocine Sales Corp, 1801/5-6 Electrical Market, Bhagirati Palace - www.escorp.in 

------------------------------------------------------------

-----------------------------------------------

LINKS & REFERENCES

* Bijli Bachao - solar panels in India - https://www.bijlibachao.com/solar/solar-panel-cell-cost-price-list-in-india.html

* Understanding Solar Power - an excellent resource that brings "Solar Power to Ordinary People"-- https://livingonsolarpower.wordpress.com/  

* Instructables - Solar charges with day-night switch - http://www.instructables.com/id/Solar-charger-with-day-night-switch-v2/

- 2N3904 NPN Transistor, linked to photo transistor and then using a 100k pot to regulate the sensitivity level.
- Day-night switch - http://www.ebay.in/itm/222242083233?aff_source=Sok-Goog
- INR 292 on EBay

- Solar charge controllers - https://www.batterystuff.com/solar-chargers/charge-controllers/

Let There Be Light

Are high pressure sodium vapour lamps more efficient than LEDs?

The key to answering this question is "Luminous Efficacy", a measure of how well a light source a Watt of electricity into Lumens, a measure of light intensity visible to the human eye.

Today, while clearing some litter at a nearby park, I came across this box -

It was lying on the grass, right below a high-mast lamp. Even though I knew that these sodium vapor lamps consumed a lot of electricity, what struck me was the quantum of light produced by these bulbs. A 400W bulb produces more than 44,000 lumens!

If this makes little sense, just compare it to the standard LED lamps being distributed by the government, in its efforts to being down household electricity  consumption -

In terms of luminous efficacy, one would have thought that the LED lamps are a lot more efficient that any incandescent, power-guzzling bulb. However, in terms of light output (lumens), the sodium vapour lamp produces 110 lumens/W while the LED lights prouduce 114 lumens/W, which is hardly any difference.

If there is not much difference in the efficiency of LED bulbs and sodium-vapour lamps, is there a big difference in cost? The sodium-vapour lamp costs INR 675 per unit while an (unsubsidized) LED lamp costs anywhere between INR 150 and 250. This means that the cost of luminous efficacy is INR 0.16 lm/W/INR for the sodium-vapour lamp and 0.57 lm/W/INR for LEDs.  

This simply means that you are getting 3.5 times more bang for your buck with LEDs, compared to sodium-vapour lamps. So it does make sense to switch to LEDs.

Now, what is the difference is cost between LEDs meantand SVs for high-mast lamps? That would berhaps perhaps be a better comparison of oranges with oranges!

-----------------------------------------
LINKS

* Energy efficiency of LEDs - http://apps1.eere.energy.gov/buildings/publications/pdfs/ssl/led_energy_efficiency.pdf

* https://en.wikipedia.org/wiki/Luminous_efficacy

* 2009 - Toshiba releases 93 lm/W bulbs - http://ledsreview.com/news/367/