Laser front projectors

vbimport

#1

Has anyone heard of when (not if) Laser front projectors will hit the consumer level? I understand some prototypes have been around for a while, but it seems to me that if lasers are so accurate and inexpensive, that front projection in a full size home theater would naturally be evolving to reality very soon. I don’t like waiting, especially when the technology has been around for years, but no one has developed a viable replacement for for LCD and Plasma. If they can make a Rear Projection system (Mitsubishi), why not front projection?


#2

Welcome aboard :slight_smile:

One of the main problems I imagine is dealing with safety, such as what happens if someone walks in front of the picture looking towards the projector. This is not possible with a laser-driven rear projection TV.

For example, a basic Class 2 laser pointer emits a tiny red dot. If you had a way of scanning that dot line by line (like a CRT) to project let’s say a 100" picture, it would probably be faintly visible in complete darkness. So to start with, we need a much brighter laser. :smiley:

The brightest laser you can safely look at the diffuse reflection (i.e. reflected on white paper) is a Class 3B rated laser, which has a limit of 500mW. For the RGB colours, the three lasers must give the same lumen rating and since our eyes see red at the weakest, we calculate the lumen of a 500mW 630nm laser as an example. I’m not sure what the ideal red wavelength is for the RGB colour spectrum, so I’m using 630nm here, which is a fairly deep red (I read somewhere that CRT red peaks around this). 630nm light has a Photopic Luminous Efficacy of 0.265, so we have the following calculation (details at this source):

[ul]
[li]0.5 x 0.265 x 683 = ~90.5 lumen[/li][/ul]

We need three lasers of equal lumen for an RGB picture, so this gives about 271 lumens. To give an idea of how bright this is, many front projectors are rated at 1000 to 2000 lumens. So to get an equivalent brightness using lasers, the projector would either need to have multiple lasers for each colour or use a shorter red wavelength at a cost of colour reproduction, as brighter Class 4 lasers (500mW up) are considered harmful to look at indirectly.

Since there is already a rear projector version, obviously they can make a front projector version. But what happens if someone walks in front of the picture looking towards the projector? A laser in excess of 5mW can cause permanent eye damage quicker than the eye can blink, so just imagine what a 500mW laser can do, since as the lasers draw the picture, each laser is shining 500mW of power at every single point for a tiny fraction of a second. So the manufacturers are likely still working on the safety, since the risk of an accidental eye injury (not mention lawsuits) is very high.