View Full Version : Semi-Newbie with a few semi-basic questions about light choice

11-03-2011, 11:06 PM
Hello everyone,

This looks like a great forum, but like all places that I have found there seems to be a great deal of (mis)information. I'm hoping to get a few things clarified. I've tried searching but can't find anything definitive. I'm going to alliterate what I have determined so far. If anything is fundamentally wrong please feel free to *politely* correct me :)

First off it's clear that just about any lighting system will work, so it's not a matter of "what works", it's "what works best for a particular situation".

Basically I'm looking to start getting into hydroponics. I want to set it up in a closet, so I have 1.5ft deep, 5ft wide and 8ft high to play with. That alone is going to affect my options. I'm looking to start with an array of basic plants and vegetables. Nothing fancy, and I can choose my plants based on what works for my lighting.

Here are some assumptions:

- I understand that frequency matters, but lets leave that aside for the moment. Let's assume that I want a normal 6500K white light spectrum for now. All systems can provide this.
- The ideal amount is 40W (or ~4400 lumens) of light per square foot.
- Electrical cost is a factor, but most of these options have the amount of energy used close enough to not really be a factor (for the prices of the fixtures given).
- HPS and MH lights project light in a circular fashion, and my needs are rectangular. LED and Fluorescent are the only ones to easily project in a rectangular manner.

Here's what I've found so far:

Complete electronic ballast systems that can use either HPS or MH bulbs (so that I can change them easily) look to be about $160 delivered. The spot nature is a problem - but even if I could spread a 150W bulb across 4 linear feet of width and that's still $40/sqf. Worse since I have 1.5ft wide and 4ft long I'd likely need a 250W system and those seem to be very rare. A 400W system delivered is $200, but again the spot nature is a problem.

The most cost effective LED that I have found seems to be a 36W LED panel which puts out 3375 lumens and it is going to cost $80 delivered. Assuming I use the maximum of 4 wide means not only $80/linear foot, but I'm at 1/2 the recommended intensity. There are higher performing panels, but they're significantly more expensive and we're already 2x the cost of everything else).

T5HO lights look promising and offer a competitive lumens/watt. But at 5200 lumens (and 1300 lumens/foot) means that I need 5 lights for the 1.5ft depth (4300 lumens/sqf) and that means about $200 per 4 linear ft of lighting or $50/linear foot.

Here's the kicker - 4x 6500K 1600 lumen spiral CFL 23W bulbs are $10 (i.e. 92W or 6400 lumens for $10) . Wiring and fixtures and a homemade reflector comes out to about $1.50 per bulb. Put 16 lights per row (1.5ft x 4ft) and that's $16/linear foot with 4300 lumens/sqf. I'm going to assume that the frequency spectrum is similar to T5HO since it's almost identical technology. I can also fit a maximum density of 16 bulbs per sqf (or 25,600 lumens, 2.5x as bright as the sun).

So since spiral CFL is so significantly cheaper (1/3rd the cost) than any other option is there any significant reason not to use this? Even if my calculations are wrong the price is so compelling.

11-07-2011, 08:34 AM
To begin, HID lamps have a light pattern controlled by a reflector which, if it is meant to be a spot light is a spot light, but if the reflector is made for large area coverage, it is not a spot light.

The long-term costs, ie, one crop of pretty much anything, dictate HID because the cost of electricity will soon overcome any difference in lamp costs. HID has the most light per watt.

11-09-2011, 10:24 PM

Thanks for the input. The problem is that reflectors are designed to spread light in a roughly square pattern, or somewhat flattened. However I'd need 1.5ft by 4ft which seems to be pretty difficult. Any light not focused into this area is wasted.

Let's assume that I can get it focused though - I'm looking at 4 shelves with a 250W system at about $170 each - or $680. Putting together a CFL system is about $200 (when buying the bulbs and fixtures in bulk). The CFLs are roughly 70 lumens / watt. The HPS systems I found were about 110 lumens/watt. Assuming that I need 4400lumens/sqf (roughly 40W/sqf of HPS) and I have 24sqf then I need 1500W of CFL vs my 1000W of HPS. Per day cost is $48/mo for HPS, $72/mo for CFL. I would need 20 months to pay off the investment.

However I can't stick with just HPS - I'd need a MH system for roughly 2/3rds of the time which is only going to provide about 90 lumens/watt. Adding $100 to the cost of setting up the system, and factoring in the reduced efficiency and my ROI for a HPS/MH system is about 4 years based on electricity consumption.

Even if I had ideal best-case HPS/MH system I'm still a minimum of 2 years for the ROI vs CFL.

11-13-2011, 08:52 AM
Even if I had ideal best-case HPS/MH system I'm still a minimum of 2 years for the ROI vs CFL.

Depends upon what you are paying for electricity. HPS operates closer to 150-200 lumens/watt in larger lamp sizes.